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!

Monday, 12 September 2011

Jagged edge - red flag

Level 1

Red flag: Jagged edge

When you find a glove and/or stocking sensory loss that has a jagged proximal edge you must consider a mononeuritis multiplex; the latter is a cause of a pseudo glove-and-stocking sensory loss.

Length-dependent sensory loss due to metabolic and toxic neuropathies usually have a sharp edge and are in proportion to each other. The following is a rough guide to proportions:

  • Foot and ankles = normal hands and arms
  • Mid calf = hands
  • Knee = mid forearm
  • Thigh = upper forearm or elbow*

* when you get length-dependent sensory loss to the level of the thighs you may find sensory loss in the mid abdomen; i.e. the disease process has started to involve the spinal nerves.

Level 2

A mononeuritis multiplex may only involve the superficial cutaneous nerves leaving the deep nerves intact; if this is the case the tendon jerks will be retained and motor involvement will be minimal.

When a mononeuritis multiplex involves the superficial cutaneous nerves only, please consider cryoglobulinaemia in the differential diagnosis. I assume you know how to take blood and process it to detect the latter; if not find out.

Mononeuritis multiplex due to vasculitis is typically very painful.

Friday, 9 September 2011


Level 1

Ataxia means unsteadiness of gait.

Ataxia is also used to describe chaotic or in-coordinated limb movements; I don't like it being used in this context.  

There are two types of ataxia; sensory and cerebellar. 

I view vestibular ataxia as being cerebellar, as the circuits involved are functionally integrated.

Romberg's test is used to distinguish between the two types; a positive Romberg's test or Rombergism (increased body sway) is diagnostic of a sensory ataxia. 

Sensory ataxia occurs as a result of a larger fibre peripheral neuropathy, dorsal root ganglionopathy, posterior radiculopathy (sensory roots) and posterior column disease. 

Tendon reflexes are lost with a neuropathy, ganglionopathy and radiculopathy, but not with pure posterior column syndromes. 

Please remember that ataxias are often mixed, i.e. both cerebellar and sensory. Examples of this are the spinocerebellar ataxias and multiple sclerosis, which can affect both the cerebellum and spinal cord.