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."