Monday, 28 November 2011

Whole brain atlas

Level 1: additional teaching resource

The whole brain atlas website, from Harvard, is a very useful resource to help you with your neuroanatomy and as a neuroradiology primer. Please refer to this site regularly. 

Evolutionary Neuroscience

Level 1: Evolutionary neurology / neuroscience

Please check-out this site: "Evolution; this view of life"

Saturday, 26 November 2011

Exercise: a possible treatment for neurodegeneration

Level 3

Spinocerebellar ataxia type 1 (SCA1) is caused by expansion of a translated CAG repeat in Ataxin-1 (ATXN1). To determine the long-term effects of exercise, this study implemented a mild exercise regimen in a mouse model of SCA1 and found a considerable improvement in survival accompanied by up-regulation of epidermal growth factor and consequential down-regulation of Capicua, which is an ATXN1 interactor. 

Conclusion: Thus, exercise might have long-term beneficial effects in other ataxias and neurodegenerative diseases.

See commentary: Gitler. Neuroscience. Another reason to exercise. Science. 2011 Nov 4;334(6056):606-7.

"The scientific case for regular aerobic exercise is compelling. Would you not agree?"

"If any of you are having problems motivating yourselves, I would suggest reading the book 'BORN TO RUN' by Christopher McDougall; you will be out running the moment you have read the book!"

Monday, 21 November 2011

Vertigo & Nystagmus with MRI

Level 3

Roberts et al. MRI magnetic field stimulates rotational sensors of the brain. Curr Biol. 2011 Oct 11;21(19):1635-40. 

Have you ever thought why patients and people get vertigo in and around MRI machines? 

Several mechanisms have been suggested to explain these sensations, yet without direct, objective measures, the cause has remained unknown, until now. 

This study has found that healthy human subjects developed a robust nystagmus while simply lying in the static magnetic field of an MRI machine. In comparison patients lacking labyrinthine function did not. 

They used the pattern of eye movements as a measure of vestibular stimulation to show that the stimulation is static (continuous, proportional to static magnetic field strength, requiring neither head movement nor dynamic change in magnetic field strength) and directional (sensitive to magnetic field polarity and head orientation). Their calculations and geometric model suggest that magnetic vestibular stimulation (MVS) derives from a Lorentz force resulting from interaction between the magnetic field and naturally occurring ionic currents in the labyrinthine endolymph fluid. This force pushes on the semicircular canal cupula, leading to nystagmus. 

They emphasize that the unique, dual role of endolymph in the delivery of both ionic current and fluid pressure, coupled with the cupula's function as a pressure sensor, makes magnetic-field-induced nystagmus and vertigo possible. 

Such effects could confound functional MRI studies of brain behavior, including resting-state brain activity.

Sunday, 20 November 2011

Babinski's sign

Level 1: The plantar or Babinski reflex is a elicited when the sole of the foot is stimulated with a blunt instrument. The reflex can take one of two forms. In normal adults the plantar reflex causes a flexor or downward response of the big toe. 

An upward response (extension) of the hallux is known as Babinski response or Babinski sign, after Joseph Babinski (1857–1932), a French neurologist of Polish origin. 

The presence of the Babinski sign is indicative of an upper motor neurone lesion. 

A Babinski sign is normal in infants and typically disappears when they start walking. 

The following YouTube clip shows you how to perform a plantar response:

Please use the back of neurotip or disposable orange stick (originally made from wood of the orange tree) to test the plantar response. The use of a tendon hammer or other non-disposable item (keys) are discouraged in the modern era as they are a potential source of hospital acquired infections. 

"In my personal experience the plantar response is not a very good sign; i.e. when there are obvious upper motor neurone signs it tends to be positive and when the plantar response is equivocal the other supporting signs (tone, power and tendon reflexes) are also equivocal."

"I was once told that 'you haven't completed your training as a neurologist unless you can make the plantar response go up or down'; this sums up the clinical utility of the sign."

"In my experience a strikingly postive or exaggerated Babinski response is typically associated with demyelinating disease. However, many other upper motor neurone lesions can cause an exaggerated response."

"Babinski actually described extension of the toe whilst walking barefoot as being the sign; I am not sure of the modern derivation."

Level 3+: There are a lot of other signs that have been described that essentially mean the same as the Babinski reflex; the following is a partial list:
  1. Bing sign – multiple pinpricks on the dorsum of the foot
  2. Cornell sign – scratching along the inner side of the extensor hallucis longus tendon
  3. Chaddock sign – stroking the lateral malleolus
  4. Gorda sign – flexing and suddenly releasing the 4th toe
  5. Gordon sign – squeezing the calf muscle
  6. Moniz sign – forceful passive plantar flexion of the ankle
  7. Oppenheim sign – applying pressure to the medial side of the tibia
  8. Schaeffer sign – squeezing the Achilles tendon
  9. Stransky sign – vigorously abducting and suddenly releasing the little toe
  10. Strümpell sign – patient attempts to flex the knee against resistance
  11. Throckmorton reflex – percussion over the metatarsophalangeal joint of the big toe
For those of you interested in the history of neurology will find the following article of interest: Joseph Babinski.

Saturday, 19 November 2011

Amateur neuroscientists

For those of you wanting to get hands on experience as experimental neuroscientists may find this site and set of experiments useful: 

Level 1: What neurological diseases are affected by changes in body temperature?

"Having in depth neuroscience knowledge enriches your clinical experience; try it!"

Saturday, 12 November 2011

Treating nystagmus

Level 3: as a follow-up to the previous posting re nystagmus

Epub ahead of printThurtell MJ, Leigh RJ. Treatment of Nystagmus. Curr Treat Options Neurol. 2011 Nov 10. 

Patients with congenital and acquired forms of nystagmus are commonly encountered in clinical practice. Many report visual symptoms, such as oscillopsia and blurred vision, which can be alleviated if the nystagmus can be suppressed.

Pharmacologic, optical, and surgical treatments are available, with the choice of treatment depending on the characteristics of the nystagmus and the severity of the associated visual symptoms. 
  1. Downbeat nystagmus can be treated with 4-aminopyridine, 3,4-diaminopyridine, or clonazepam
  2. Upbeat nystagmus can be reduced with memantine, 4-aminopyridine, or baclofen
  3. Torsional nystagmus may respond to gabapentin
  4. Acquired pendular nystagmus in patients with multiple sclerosis is often partially suppressed by gabapentin or memantine
  5. Acquired pendular nystagmus in patients with oculopalatal tremor can respond to gabapentin, memantine, or trihexyphenidyl
  6. Although acquired periodic alternating nystagmus is often completely suppressed by baclofen, memantine can be effective in refractory cases. 
  7. Seesaw nystagmus can be reduced with alcohol, clonazepam, or memantine
  8. Infantile nystagmus may not cause significant visual symptoms if "foveation periods" are well developed, but the nystagmus can be treated in symptomatic patients with gabapentin, memantine, acetazolamide, topical brinzolamide, contact lenses, or base-out prisms to induce convergence.
  9. Several surgical therapies have also been reported to improve infantile nystagmus syndrome (INS), but selection of the appropriate therapy requires preoperative evaluation of visual acuity and nystagmus intensity in different gaze positions. 
  10. Other treatment options for nystagmus include botulinum toxin injections into the extraocular muscles or retrobulbar space. 
  11. Electro-optical devices are currently being developed, in order to noninvasively negate the visual consequences of nystagmus.
"This paper makes it seems that nystagmus responds well to pharmacological therapies. In my experience this is not the case; the response is usual moderate and most of the drugs come with side effects that prevent higher doses."

Tuesday, 8 November 2011

Nerves in the superior orbital fissure

Level 2:

1. Lacrimal nerve (Vi)
2. Frontal nerve (Vi)
       Superior ophthalmic veins
3. Trochlear nerve (IV)
4. Superior division of oculomotor nerve (IIIs)
5. Nasociliary nerve (Vi)
6. Inferior division of oculomotor nerve (IIIi) + parasympathetic fibres
7. Abducens nerve (VI) + sympathetic fibres
       Inferior ophthalmic veins
"A blast from my past!  Does anyone recall the dirty mnemonic that helps you remember the structures that pass through the superior orbital fissure? If you do please share with us."

"I will post a case study in the next few days that will illustrate why you should try and remember the anatomy of this structure."

Extra reading: superior orbital fissure

Sunday, 6 November 2011

The philosophy of a blog

A blog is a two-way street; if you don't make comments and enter into a dialogue with the blogger and other readers it will be less valuable or at worst it will die. 

Please feel free to ask as many questions as you want and please make suggestions; requests are welcome.

I am new to using a blog as a teaching forum so any feedback would be very helpful. Do you want more, or less posts? Are the post too superficial or too detailed? Do you like the idea of three levels? etc.

Case study: 6th nerve palsy and ptosis

A 67-year old lady presented to the accident and emergency department with horizontal double-vision on looking to the left. When examined she was found to have a left sixth nerve palsy and mild ptosis of the left eye. When she was examined by the neurologist they confirmed the 6th nerve palsy and felt she also had features of a Horner's syndrome.

Level 1

What are the clinical features of a Horner's syndrome?
Where is the lesion?

Level 2

What is the most likely diagnosis?

Level 3

Describe the sympathetic innervation of the orbit and eye?
Is the Horner's syndrome pre or post ganglionic and what pharmacological tests can be done to localise the lesion?


Recommended revision: How to examine eye movements (including the use of the alternate cover test) and the pupils and the neuroanatomy of the cavernous sinus, superior orbital fissure and sympathetic and parasympathetic innervation of the orbit.

Thursday, 3 November 2011

Hoover's sign

Level 1:

Hoover’s sign of leg paresis is one of two signs named after Charles Franklin Hoover (1865–1927), an American physician, born in Cleveland, Ohio, who studied medicine at Harvard.

The manoeuvre is aimed to separate organic or non-functional from non-organic or functional paresis of the leg. The sign relies on the principle of synergistic contraction of muscle groups. Involuntary extension of the "paralysed" leg occurs when flexing the contralateral leg against resistance. 

The figure below explains the principles of the test. If the patient has weakness when you test extension of the right leg (A) but has detectable power in the right leg when you test flexion of the left leg (B) it implies that the patient is likely suffering from non-organic limb weakness (positive Hoover's sign). In B the extension of the right leg occurs due to involuntary contraction of synergistic muscles. 

I find a positive Hoover's sign a very useful clinical test to confirm a clinical suspicion of non-organic or medically unexplained symptoms. Please remember that a large number of patients may still have a organic disease despite a positive Hoover's sign; patients often try to enhance, or exaggerate, their symptoms and signs to make you take their complaints seriously; the medical jargon for this is "functional overlay". The diagnosis of medically unexplained symptoms is often very difficult; please don't rush to make this diagnosis particularly if you have any doubts. 

For those of you doing general medicine a positive Hoover’s sign may refer to inward movement of the lower rib cage during inspiration, implying a flat, but functioning, diaphragm. This is typically associated with hyperexpansion of the lungs due to air trapping, particularly emphysema. The flattened diaphragm contracts inwards instead of downwards, thereby paradoxically pulling the inferior ribs inwards with its movement.

Tuesday, 1 November 2011

Case study: diplopia and the alternate eye cover test

Apologies for not posting last week; I was away.

A 32 year old woman with relapsing-remitting multiple sclerosis (MS) presents with a 2 week history of horizontal double vision on looking to the right; the images were overlapping with the blurred or false image to the right.

Level 1

What and where is the lesion?

What is the alternate eye cover test?

What other clinical sign could this patient have and why?


Wednesday, 19 October 2011

Abdominal Reflexes

Level 1: in response to an outpatient teaching session last week.

The abdominal reflexes refers to the reflex stimulated by the stroking of the abdomen around the umbilicus that results in contraction of the abdominal muscles; typically the umbilicus moves towards the source of the stimulation. 

How do you perform the reflex? 

Stroke the abdomen lightly on each side in an inward direction above and below the umbilicus using a orange stick (wooden stick) or blunt end of a neurotip (figure below). When you do the reflex the patient should be lying down and relaxed with their arms by their sides.

Remember all reflexes have an afferent and an efferent limb; in the case of the abdominal reflexes the afferent is cutaneous sensory (tickle and light touch) that is dermatomal and the efferent limb is the segmental innervation of the abdominal muscles. 

I was always taught that the abdominal reflex was a short spinal arc; this however this does not explain why the reflex is typically lost in upper motor neurone syndromes. Loss of the reflex may be abnormal. In contrast, the presence of the reflex is normal.

This reflex is also lost due to a variety of causes, including age, abdominal surgery, obesity, pregnancy and in parous woman. I therefore don't find absent abdominal reflexes a very helpful clinical sign. Their presence on the other hand is very reassuring; particularly when you think the patient has medically unexplained symptoms and signs. In my personal experience the presence of the abdominal reflexes is predictive no significant upper motor neurone pathology. Again don't rely on one sign to make this call; the abdominal reflexes have the be integrated with the remainder of your findings. 

The following YouTube video describes and shows how to perform the reflex; this is not how I was taught to do the reflex. I was taught to do only test in 4 quadrants; this demonstration breaks the abdomen up into several sectors; I personally don't think that this is necessary.

Occasionally I have found the abdominal reflexes helpful as a localising sign in patients with thoracic cord lesions; i.e. upper reflexes are intact and the lower reflexes are lost. However, a detailed sensory examination is usually better at localising a specific level than the abdominal reflexes.

Please note that the reflex fatigues or habituates; in other words with repeated stimulation the reflex disappears. So don't be alarmed if your friend finds the reflex and when you try it is not there. 

What is the evolutionary role of the abdominal reflexes? 

I was taught that the local contraction of the abdominal muscles to an abdominal sensory stimulus was to protect the internal viscera from damage. To test this theory you should try and punch each other lightly in the abdomen; you will soon realise that you can't control the reflex contraction of the muscles.  

Monday, 17 October 2011

A hexanucleotide expansion on #9p21 causes ALS-FTD

Level 3: For those of you who missed Huw Morris' presentation at the ABN in Newcastle.

Epub ahead of printRenton et al. A Hexanucleotide Repeat Expansion in C9ORF72 Is the Cause of Chromosome 9p21-Linked ALS-FTD. Neuron. 2011 Sep 21.

The chromosome 9p21 amyotrophic lateral sclerosis-frontotemporal dementia (ALS-FTD) locus contains one of the last major unidentified autosomal-dominant genes underlying these common neurodegenerative diseases. The investigators have previously shown that a founder haplotype, covering the MOBKL2b, IFNK, and C9ORF72 genes, is present in the majority of cases linked to this region. Here they show that there is a large hexanucleotide (GGGGCC) repeat expansion in the first intron of C9ORF72 on the affected haplotype. This repeat expansion segregates perfectly with disease in the Finnish population, underlying 46.0% of familial ALS and 21.1% of sporadic ALS in that population. Taken together with the D90A SOD1 mutation, 87% of familial ALS in Finland is now explained by a simple monogenic cause. The repeat expansion is also present in one-third of familial ALS cases of outbred European descent, making it the most common genetic cause of these fatal neurodegenerative diseases identified to date.

"This will almost certainly be the neurology paper of the year. The finding will now allow pre-symptomatic diagnosis, the creation of new animal models and hopefully new insights into MND-ALS-FTD that will ultimately lead to a treatment."

Extra-curricular reading for Medical Students: MND, FTD

Sunday, 16 October 2011

Tendon Reflexes

Level 1: in response to watching the technique of a year 4 medical student in outpatients:

1. When performing any part of the neurological examination you need to know the anatomy and neurophysiology of  what you are testing. All reflexes have an afferent and efferent arm (please learn the anatomy of the afferent and efferent limbs of all reflexes you test; neurology becomes a lot easier when you know things).

The tendon reflex is a monosynaptic stretch reflex; it is activated by stimulating the golgi tendon organ a stretch receptor. The afferent signal then passes via a large sensory fibre (type Ib), which conducts rapidly (80-120m/sec), to the spinal cord via the posterior roots.  A branch of the axon synapses directly on a local population of anterior horn cells to elicit a motor response. Other axonal branches of the Ib sensory axon generates supraspinal responses, via interneurons and ascending tracts, to control muscle contraction and movement (e.g. anterior and posterior spinocerebellar tracts).

2. Know the muscle (tendon) and the corresponding motor root and nerve for each reflex you are testing:

Commonly tested reflexes:

1. Biceps - C5/6, musculocutaneous nerve
2. Triceps - C6/7/8, radial nerve
3. Brachioradialis/supinator - C5/6, radial nerve (please note when you test the brachioradialis reflex you also activate the supinator muscle)
4. Knee jerk - quadriceps muscle, L3/4, femoral nerve
5. Ankle jerk - gastrocnemius and soleus muscle, S1 (minor contribution from L5 and S2), posterior tibial nerve (I was always taught that this was the only reflex that you could quote as having only one root level, i.e. S1)

Less commonly tested:

1. Deltoid - axillary nerve, C5/6
2. Pectoral - medial and lateral pectoral nerves, C5/6 (clavicular head) & C7/8, T1 (sternocostal head)
3. Finger jerks - long finger flexors (flexor digitorum profundus and superficialis), C8/T1, median and ulnar nerves
4. Adductor - hip adductors (longusmagnus,brevis), L2/L3, obturator nerve
5. Hamstring - hamstrings (semitendinosus, semimembranosus, biceps femoris), L5/S1, sciatic nerve

Tip: you may find the the muscle database for nerve and root levels a helpful resource.

3. Which reflex or patella hammer should you use? I am not fussy, but would recommend the Queen Square hammer below. It is flexible and allows you to achieve momentum compared to the short rigid hammers. This makes it easier to use and ensures you are some distance away from the tendon and muscle to observe the motor response.

4. How to do a reflex? Please see the video below. Always compare left and right reflexes with each other. When doing the reflex watch the muscle and limb to see movement. You should also hold the limb in a relaxed way that also allows you to feel the reflex.

"When examining medical students it easy to tell apart students who have practised doing reflexes from those who have not. The neurological examination is like any other skill; you need to do it over and over again until you get good at it."

5. Grading reflexes:

Grade 4: markedly increased, associated with sustained clonus and spread to other muscle groups
Grade 3: increased, associated with non-sustained clonus
Grade 2: easily elicitable
Grade 1: depressed, but elicitable with reinforcement (Jendrassik maneuver)
Grade 0: absent

6. Know what is normal and interpret the reflexes in the clinical context.

All reflex grades described above can be normal. For example, athletes completing the 100m sprint, or someone who has had a fright that has resulted in an increase adrenergic drive, will have increased tendon reflexes, possibly with clonus. These are normal physiological motor responses. Similarly, the elderly will have depressed reflexes and possibly absent ankle jerks (absent ankle jerks are considered normal over the age of 65 in the absence of other neurological signs except reduced vibration sensation to the level of the ankle). Depressed reflexes in the presence of a glove and stocking sensory loss is abnormal and indicates a peripheral neuropathy. Increased tendon reflexes in the presence of pyramidal weakness is a sign of an upper motor neurone lesion. Increased reflexes in association with thyrotoxicosis is due to physiological enhancement of the reflex and is not abnormal. These few examples illustrate that the tendon reflexes need to be interpreted in context; don't jump to premature conclusions before completing the neurological examination and assimilating all information you have at hand.

"I find doing the reflexes after examining the muscle tone, muscle power and sensory modalities most useful. This provides you with information on the afferent and efferent limbs of the tendon reflex before examining and interpreting the reflexes. The classic teaching is to do the tendon reflexes as part of the motor examination, before sensory testing."

Ankle Clonus

Knee Clonus

7. History of the tendon hammer: I would encourage you to read this short piece on the history of the tendon hammer. Danielle Goldberg, a student from Glasgow, wrote it as a library project during her medical elective in July 2010.

Friday, 14 October 2011

Alcohol myopathy

In response to recent bedside teaching on a middle-aged man with alcoholic cerebellar degeneration. He also had evidence of a proximal myopathy. 

Level 2: Urbano-Marquez et al. The effects of alcoholism on skeletal and cardiac muscle. N Engl J Med. 1989 Feb 16;320(7):409-15.

This study was performed to determine the prevalence of alcoholic myopathy and cardiomyopathy. They studied a group of 50 asymptomatic alcoholic men (mean age, 38.5 years) entering an outpatient treatment program. Studies performed included an assessment of muscle strength by electronic myometer, muscle biopsy, echocardiography, and radionuclide cardiac scanning, with comparison to healthy control subjects of similar age. The patients' mean (+/- SEM) daily alcohol consumption was 243 +/- 13 g over an average of 16 years. These patients had no clinical or laboratory signs of malnutrition or electrolyte imbalance. 42% of the patients, as compared with none of the controls, had strength of less than 20 kg as measured in the deltoid muscle. Muscle-biopsy specimens from 23 patients (46%) had histologic evidence of myopathy. In the cardiac studies, when the alcoholic patients were compared with 20 healthy controls, the patients had a significantly lower mean ejection fraction (59% vs. 67%), a lower mean shortening fraction (33 vs. 38 percent), a greater mean end-diastolic diameter (51 vs. 49 mm), and a greater mean left ventricular mass (123 vs. 106 g per square meter of body-surface area). One third of the alcoholics had an ejection fraction of 55 percent or less, as compared with none of the controls. Endomyocardial biopsy specimens from six patients with ejection fractions below 50 percent showed histologic changes of cardiomyopathy. The estimated total lifetime dose of ethanol correlated inversely with muscular strength (r = -0.65; P less than 0.001). In an analysis that also included six patients with symptomatic alcoholic cardiomyopathy, the estimated total lifetime dose of ethanol correlated inversely with the ejection fraction (r = -0.58; P less than 0.001) and directly with the left ventricular mass (r = 0.59; P less than 0.001). The Investigators' conclude that myopathy of skeletal muscle and cardiomyopathy are common among persons with chronic alcoholism and that alcohol is toxic to striated muscle in a dose-dependent manner.

"This study illustrates how common alcoholic myopathy is and in my experience it is often missed at the bedside. The best way to screen for it is to: (1) test power of shoulder abduction, (2) ask the patient to attempt a sit-up with arms folded across the chest and (3) to perform a squat. These manoeuvres typically bring out proximal and truncal weakness."

Cerebellar eye signs

Level 1 to 3

The following is a list of cerebellar eye signs; I suggest you remember them using a systematic approach to the examination of the eye movements:

Position of eyes in the neutral position with vision fixated in the distance:

1. Square-wave jerks: the eyes drift of their target in randomly and a quick saccade pulls the eyes back to the neutral position. When the jerks are only seen when looking at the optic disc with an ophthalmoscope they are referred to as micro-square wave jerks.

2. Distance esotropia; this is the term used to describe double vision that is present on looking into the distance but disappears with convergence and near vision.

3. Skew deviation; ocular deviation where the eyes move upwards (hypertropia), but in opposite directions.
Skew Deviation

Horizontal eye movements:

3. Gaze-evoked jerk nystagmus; this typically changes direction across the mid line. Please note that nystagmus due to peripheral vestibular lesions is usually worse to side of the lesion and does not change phase across the midline. The slow phase of nystagmus the abnormal phase with the fast phase the corrective phase.

4. Jerky pursuit eye movements; this is also referred to as saccadic intrusion. Pursuit eye movements are made up of many small saccades.

5. Slow saccades; there is a delay in starting the saccades and they are slow. Please note that a delay in initiating saccadic eye movements can also occur due to lesions of the frontal lobes that affect the frontal eye fields (voluntary saccades). In cerebellar disease both voluntary and involuntary saccades (in response to head movements) are slow.

6. Saccadic dysmetria; hypometric saccades refers to undershoot or not reaching the target and hypermetric saccades to overshoot or going past the target. This is the visual equivalent of what happens in the limbs.

7. Inability to suppress the vestibular-ocular rreflex (VOR); please see previous post on the VOR.

Additional web materialRobert B. Daroff Collection

Vestibulo-ocular reflex (VOR)

Level 1

The vestibulo-ocular reflex (VOR) is a reflex eye movement that stabilizes images on the retina during head movement.

To understand the VOR you will need revise your anatomy of the vestibular apparatus; the following video will help.

The VOR produces an eye movement in the direction opposite to head movement, thus preserving the image on the center of the visual field. For example, when the head moves to the right, the eyes move to the left, and vice versa.

The vestibulo-ocular reflex. A rotation of the head is detected, which triggers an inhibitory signal to theextraocular muscles on one side and an excitatory signal to the muscles on the other side. The result is a compensatory movement of the eyes.
To detect dysfunction of the semicircular canal we use the simple head impulse test (also called the head thrust test, or the Halmagyi-Curthoys test, or the Halmagyi test). The patient fixes their vision on a target and the head is turned to the left or right. Normally the eyes remain fixed in the object; the presence of a catch-up saccade or saccades is abnormal. 

As slight head movements are present all the time, the VOR is very important for stabilising vision: subjects whose VOR is impaired find it difficult to read, because they cannot stabilise the eyes during small head tremors and this results in oscillopsia.

The VOR reflex does not depend on visual input and works even in total darkness or when the eyes are closed.

VOR suppression testThis test assesses the ability of the vestibulocerebellar system to suppress a vestibular signal. It is assessed by asking patients to follow with the head in the same direction an object that rotates; for example the patient looks at their outstretched hands held together while seated in a chair that rotates. If the vestibulocerebellum is intact then the eyes remain stable in the orbit, with their vision fixed on their outstretched hands, due to suppression of the VOR. In central vestibulocerebellar pathology, this test typically reveals pursuit eye movements, with saccadic intrusions, associated with the presence of  a breakthrough nystagmus during head rotations as fixation is incomplete.

Head Shake Test: Rapid horizontal head shaking for 15 to 20 seconds occasionally results in horizontal post-headshake nystagmus usually (but not always) directed away from the side of a unilateral vestibular loss. When done in specialist clinics Frenzel’s glasses are typically worn whilst doing this test to prevent ocular fixation that can suppress the nystagmus. Headshake nystagmus is  generally thought to occur when asymmetries in resting vestibular tone are exaggerated via brainstem control mechanisms.

Frenzel's goggles
Extra reading: Physiology of the Vestibular System, by John Rutka

Friday, 7 October 2011

Case study: Upper Limb 2

A 58 year old Afro-Caribbean shop keeper who complains of pain, numbness and weakness in her right hand ongoing for three years.

The pain is felt in the palmar aspect of the lateral 3 1/2 digits of the right hand, it is constant and sometimes wakes her at night. The finger tips are completely numb. At work, she does everything using the other hand because the right hand is too weak to grip things and is very clumsy. She has a history of hypertension and arthritis. In the past she had received steroid injection in the wrist which produced temporary relief.

For the rest of the scenaro, please click here.

Sunday, 2 October 2011

Focal myokymia is not always benign

Level 3

Epub ahead of printBarmettler et al. Eyelid Myokymia: Not Always Benign. Orbit. 2011 Sep 29.

A 33-year-old otherwise healthy male presented with a week-long history of isolated right lower eyelid myokymia. Two weeks later, the patient's myokymia had progressed to include twitching of the right brow and right upper lip. Imaging revealed multiple demyelinating lesions consistent with multiple sclerosis. A review of eyelid and facial myokymia, along with possible concerning causes is provided, geared towards the oculoplastic surgeon. Eyelid myokymia, typically a benign condition, may rarely evolve into facial myokymia reflective of underlying brainstem disease.

"I have always taught that focal myokymia is benign and does need investigation. Almost everyone recalls having an episode themselves. As a runner I tend to get focal myokymia frequently after a long run. Focal myokymia is often related to stress, excessive caffeine intake and sleep deprivation."

"Superior oblique myokymia presents with intermittent oscillopsia and dilopia that is characteristic; the images shimmer with a vertical deviation."

"Please don't get focal myokymia mixed up with facial myokymia, which is unilateral rippling movements across the facial muscles this is much more sinister and usually indicates brain stem pathology, for example demyelination."

"An important learning point is that patients, in particular healthcare professionals, think focal myokymia is due to fasciculations and that they have motor neurone disease. In general fasciculations cannot be felt and can only be seen. The exception to the latter is macro-fasciculations that occur when the anterior horn cell innervating very large motor units degenerate; this typically occurs in the post-polio syndrome."

"If treatment is necessary, for example in superior oblique myokymia, I would recommend carbamazepine or oxcarbazepine. In theory other sodium channel blockers should also be effective." 

Thursday, 29 September 2011

Lumbar Puncture

Level 1

Cerebellar signs

Level 1: As a follow-up to the case of alcoholic cerebellar degeneration we saw yesterday.

The mnemonic you need to remember is VANISH-3D or VANISH-DDD

V - Vertigo
A - Ataxia (remember it should be Romberg's negative)
N - Nystagmus (horizontal gaze-evoked jerk nystagmus that typically changes phase across the mid-line)
I - Intention tremor
S - Slurred or Staccato Speech
H - Hypotonia (this refers to static not dynamic tone)
D - Dysmetria
D - Dysdiadochokinesia
D - Dysarthria

Tuesday, 27 September 2011

L'hermitte's sign

Level 1: In response to a query in outpatients today regarding L'hermitte's sign.

Spinal cord disease: L'hermitte's sign is the electric shock-like sensation that runs down the back and into the limbs on flexion of the neck. It is non-specific and simply indicates pathology of the posterior columns* of the spinal cord. In young adults it usually occurs in association with demyelination and other inflammatory myelopathies. However, it can occur as a result of compressive myelopathy, radiation myelopathy, subacute combined degeneration of the spinal cord (vB12 deficiency), copper deficiency, tumours, etc. Reverse L'hermitte's sign is when the shock-like sensation radiates up the spine; this is due to involvement of the posterior columns lower down the spinal cord.

*"Please note that posterior columns, not dorsal columns, is the correct anatomical term used to describe human anatomy. Dorsal and ventral terms should be restricted to describe veterinary anatomy; spot the error in the labelling of the diagram below. Unfortunately, dorsal is so entrenched in the human anatomy jargon that it is unlikely to be replace sometime soon by the exclusive use of posterior."

Frontal lobe disease:

Another eponymous sign that is also sometimes called L'hermitte's sign, or preferably L'hermitte's frontal lobe sign, is utilisation behaviour. Patients inappropriately grab objects, but use them appropriately. This occurs as a result of unilateral or bilateral frontal lobe lesions. Utilisation behaviour often occurs in association with imitation behavior; the inappropriate imitation of certain task or posture.

Utilisation behaviour: (A) Bilateral infarction of the territory of Huebner's artery; old haematoma of the medial part of the corpus callosum; bilateral demyelination of the white matter. (B) Smoking behaviour. (C) Putting glasses on the nose. (Compston Brain (2005) 128(1): 3-4 doi:10.1093/brain/awh361)

History of Neurology: Jean L'hermitte (1877 - 1959) was born in Mont-Saint-Père, studied in Paris and graduated in medicine in 1907. He specialised in neurology and became Chef-de-clinique (resident) for nervous diseases in 1908, Chef de laboratoire in 1910, and professeur agrégé for psychiatry1922. He later became Médecin des Hôpitaux at the "Hospice Paul Brousse", head of the foundation "Dejerine", and clinical director at the Salpêtrière Hospital.

Sunday, 25 September 2011

Pseudo sixth nerve palsies

Level 1: We had a very engaging grand round from our neuro-ophthalmologist, Nadeem Ali, on Thursday.  He presented a case of convergence spasm. This reminded me of a case I saw when I was a trainee when I made an incorrect diagnosis of bilateral 6th nerve palsies, when the patient actually had convergence spasms.

The clue to this diagnosis is that when the try and ask the patient to abduct the eye they can't and the eye movements are associated with a rather bizarre jerky nystagmus; the nystagmus is not regular and the jerks occur at a lower frequency. The clue to the diagnosis is that the pupils are noted to constrict and the vision for distant objects will blur. Convergence spasms occurs as a result of the activation of the accommodation or triple reflex; (1) adduction of the eyes (medial recti), constriction of the pupil (constrictor pupillae)  and accommodation (ciliary muscle). As a result of the accommodation reflex the visual acuity for distant objects changes, i.e. in abduction the patient develops a myopia and needs a concave lens (negative dioptres) to correct the vision.

Although convergence spasms is usually not due to "organic disease" and work-up is negative (Sarkies and Sanders, 1985), its response to botox has led some to consider it a form of dystonia (Kaczmarek, 2009). However, convergence spasms can be associated with organic pathology (Guiloff et al., 1980), for example trauma, multiple sclerosis and other brainstem pathology.

Please don't assume that convergence spasms is due to "hysteria" or is "functional", this is what is printed in most text books.

Friday, 23 September 2011

Taste perception

Level 3Chen et al. A gustotopic map of taste qualities in the mammalian brain. Science. 2011 Sep 2;333(6047):1262-6.

Taste is one of our fundamental senses, responsible for detecting and responding to sweet, bitter, umami, salty, and sour stimuli. In the tongue, the five basic tastes are mediated by separate classes of taste receptor cells each finely tuned to a single taste quality. These investigators explored the logic of taste coding in the brain by examining how sweet, bitter, umami, and salty qualities are represented in the primary taste cortex of mice. They used in vivo two-photon calcium imaging to demonstrate topographic segregation in the functional architecture of the gustatory cortex. Each taste quality is represented in its own separate cortical field, revealing the existence of a gustotopic map in the brain. These results expose the basic logic for the central representation of taste perception.

Gustatory cortical map in the mouse: bitter (red), salty (orange), umami (yellow), and sweet (green) taste in the mouse gustatory cortex.

"This findings of this paper are not surprising considering how other primary sensory cortices are laid out. Despite this the findings are proving quite controversial."

"What about the neurology of taste? Are you all up to speed on gustatory seizures, ageusia (complete loss of taste), hypogeusia (diminished sense of taste), hypergeusia (enhanced gustatory sensitivity), dysgeusia (qualitative gustatory disturbance relating to a distorted taste perception or to a persistent taste sensation in the absence of stimulation) and phantogeusia (taste phantoms)?"

Thursday, 22 September 2011

Sciatic nerve anatomy

Level 1: The clinical case at today's grand round presented with bilateral sciatica due to an extradural paraganglioma. An opportunity was missed to remind you of the anatomy of the sciatic nerve and how to perform a straight leg raising test; please revise.

Straight leg raising test

Genomic Medicine - carbamazepine

Level 1: I read the following review article in the NEJM on genomic medicine:

Hudson KL. Genomics, health care, and society. N Engl J Med. 2011 Sep 15;365(11):1033-41.

The following is a statement from table 2, which is based on the FDA alert below:

FDA ALERT [12/12/2007]: Dangerous or even fatal skin reactions (Stevens Johnson syndrome and toxic epidermal necrolysis), that can be caused by carbamazepine therapy, are significantly more common in patients with a particular human leukocyte antigen (HLA) allele, HLA-B*1502. This allele occurs almost exclusively in patients with ancestry across broad areas of Asia, including South Asian Indians. Genetic tests for HLA-B*1502 are already available. Patients with ancestry from areas in which HLA-B*1502 is present should be screened for the HLA-B*1502 allele before starting treatment with carbamazepine. If they test positive, carbamazepine should not be started unless the expected benefit clearly outweighs the increased risk of serious skin reactions. Patients who have been taking carbamazepine for more than a few months without developing skin reactions are at low risk of these events ever developing from carbamazepine. This is true for patients of any ethnicity or genotype, including patients positive for HLA-B*1502. This new safety information will be reflected in updated product labeling.

"This is something new to me and worth remembering in UK neurology practice, considering the ethnic diversity of the our population."

Wednesday, 21 September 2011

Referred pain from the sphenoid sinus

Red flag: Please note that sphenoid sinusitis often results in referred pain to the vertex of the head; the junction between Vi and C2 dermatomes.

Innervation of the sphenoid sinus: Sensory innervation is by the posterior ethmoidal nervesPostganglionic parasympathetic fibres of the facial nerve that synapse in the pterygopalatine ganglion control mucous secretion.

Level 1

What is the biological function of the paranasal sinuses?

In clinic yesterday I saw a patient with headache and a mucocoele in one of the paranasal sinuses. Given how many medical problems are associated with the paranasal sinuses I asked the students sitting in with me about what the biological function of the paranasal sinuses is. The responded by stating that the sinuses make the skull lighter and improve the resonance of spoken speech.

A quick look at the wikipedia lists the following:
  1. Decreasing the relative weight of the front of the skull, and especially the bones of the face.
  2. Increasing resonance of the voice.
  3. Providing a buffer against blows to the face.
  4. Insulating sensitive structures like dental roots and eyes from rapid temperature fluctuations in the nasal cavity.
  5. Humidifying and heating of inhaled air because of slow air turnover in this region.
I suspect all of these are acquired secondary functions. However, the main evolutionary driver is their role as a heat exchanger in relation to the carotid rete to cool the blood going to the brain. Have you heard of a rete? if not, please read the entry on this the section on our wiki on evolutionary neurology

Level 1: What are the biological functions of paranasal sinuses? Answer

Level 3: What is a carotid rete? Answer

Thursday, 15 September 2011

Case study: upper limb

25 year old Caucasian male presented with 8 week history of left arm stiffness and pain, tingling and numbness in the thumb and index finger of his left hand.

Prior to onset of symptoms he had been in a surfing accident, his left arm was forcefully abducted with sudden onset pain in the shoulder. The following morning his left arm seemed to 'seize-up' with shooting pains travelling down the length of the arm into the fingertips. There was no feeling in the thumb or index fingers of the left hand, albeit mild tingling which was present constantly. Over the next couple of weeks there was improvement in strength but with significant residual weakness.

O/E the left hand was smaller than the right, there was marked wasting of the abductor pollicis brevis (APB) and forearm flexors. Power in the proximal muscle groups was normal. He was unable to form a tightly folded fist in the left hand or the shape of an 'O' between the left thumb and index finger. There was also weakness of thumb abduction and finger flexion/extension, and forearm pronation. Sensory loss was confined to the left thumb and index finger.

Nerve conduction studies revealed a post-ganglionic lesion involving the median nerve, medial antebrachial cutaneous nerve and motor fibres of radial nerve.

Level 1

1) Localise the lesion?

2) What is the cause?

3) What is the treatment?

Tuesday, 13 September 2011

Are you a neurophobic?

Neurophobia is the fear of neuroscience and clinical neurology.

The term was coined by Jozefowicz in 1994.

Jozefowicz RF. Neurophobia: the fear of neurology among medical students. Arch Neurol. 1994 Apr;51(4):328-9.

About 1 in 2 medical students suffers from the condition. 

Neurophobia results in an aversion to neurological cases in the clinical setting. This is a problem as ~30% of patients passing through medical casualty have a neurological problem. All medical graduates need a basic level of competency in neurology. 

Cyriac Athappilly recently completed an intercalated BSc, in Medical Education, at Barts and The London, on neurophobia. He concluded that we need to do the following to address the issue of neurophobia in medical students: 
  1. To introduce neurology to students as soon as possible in the medical curriculum 
  2. To include it in all years of study 
  3. To make sure neuroanatomy is taught well and in sufficient detail 
  4. To arrange more one-to-one teaching
This blog is part of  an experiment to provide asynchronous clinical neurology teaching to help address the issue of neurophobia. It will be used as a tool to bridge theoretical and clinical neurology teaching. It will be combined with a neurology teaching wiki that will provide more context to the postings on this blog.

The information will be provided on three levels:
  • Level 1: medical students and general practitioners 
  • Level 2: medical specialist registrars and medical consultants
  • Level 3: neurology registrars and neurology consultants
The success of the blog will depend on your participation; i.e. registering for email notifications and posting comments. 

We hope you enjoy it!