Question 27

College answer

Discussion

a)    List five neurological signs associated with a lateral medullary infarction. (25% marks)

All the classical stroke syndromes can be found listed and described here.

The latery medullural syndrome (Wallenberg syndrome) consists of the following classical findings:

• On the side of the lesion:
  • Facial sensory loss
  • Nystagmus
  • Horner's syndrome
  • Loss of gag reflex
  • Ipsilateral ataxia with a tendency to fall to the ipsilateral side
• On the contralateral side:
  • Pain and temperature sensory loss in the extremities
• Generally:
  • Vertigo
  • Nausea
  • Dysphagia

b)    List four neurological signs of a third cranial nerve palsy. What clinical feature of the palsy would distinguish between an intracranial mass lesion or diabetic neuropathy as the cause?    (20% marks)

Lesions of the oculomotor nerve (CN III) include the following features:

• Ptosis
• Down-and-out pupil
• Mydriasis
• Failure of light reflex
  (but consensual constriction of the opposite eye is intact)
• Failure of accommodation

The college mention that "A mass lesion results in pupillary non-reactivity, in diabetes the pupil is spared". This is accurate: diabetes and other forms of microvascular disease cause a pupil-sparing oculomotor palsy. This is because the nerve's central core underoes ischemic infarction (authoritative source).

c)    List five neurological deficits associated with a bulbar palsy, along with the corresponding cranial nerves which are affected.    (25% marks)

This is an exercise in listing the bilateral lower motor lesions of nerves 9, 10, and 12. these data come from an article by 

Absent gag reflex: due to bilateral lesions of CN IX and X

Soft palate paralysis which results in "im­precise consonants, hypernasality, and a decreased range of pitch and loudness" (because the weakness of the soft palate and pharyngeal muscules causes insufficient nasopharyngeal closure and reduced oral airflow). The resulting speech is breathy, quiet and the patient is generally unable to generate long phrases because they need to pause to take another breath. This is due to bilateral lesions of CN IX and X; a unilateral lesion of the same mechanism would cause a deviation of the uvula.

Paralysis of the laryngeal muscles: this causes a "soft, weak, low-pitched and
mono­tonous voice" which is the result of CN X paralysis. In bulbar palsy the volcal cords are hypoadducted, which promotes aspiration.

Tongue wasting and fasciculations due to CN XII paralysis; which also contributes to the inarticulate speech.

Dysphagia occurs because the process of swallwoing normally requires all the bulbar nerves to work in concert, and their weakness therefore results in an incoordinated swallow. Realistically, this is due to the dysfunction of nerves IX, X and XII, but also V and VII.

Drooling, because there is a loss of tone and strength in the muscles that control lip closure (CN VII). At the same time, due to decreased laryngeal sensitivity and motor function, there is progressive pooling of food and saliva in the vallecula and piriform recesses.

d)    List six causes of dilated unreactive pupils not due to a primary intracranial lesion.
(30% marks)

Not due to an intracranial lesion would exclude all the usuals suspects:

• That is what the end of brainstem herniation looks like
• Bilateral midbrain lesion- eg. basilar artery infarct
• Bilateral 3rd nerve damage, eg. due to severe base of skull fracture

 Thus, you are left with a list of differentials which could be massively broad:Fortunately, Critical Care and Resuscitation published a case report by a P.D. Thomas (2000) which fits this SAQ like a glove.  Thomas' original classification is reproduced below, as well as a complimentary list which covers similar ground.

An alternative classification might follow a classical mnemonic for differential diagnosis, as this is what an exam candidate may fall back on when under stress.

• Vascular problems:
  • Spinal infarction 
  • Severe global brain injury (eg. due to hypoxia)
• Infectious causes
  • Botulism
  • Syphilis (uveitis or neurosyphilis)
  • Tetanus
• Neoplasms
  • Bilateral retinoblastoma
• Drug-induced causes
  • Anticholinergic drugs, topically or systemically
  • Sympathomimetic drugs
  • Serotonin syndrome
  • Toxins from classican Strayan fauna: funnel web spider, taipan, blue-ring octopus, as well as tetrodotoxin 
• Idiopathic causes
  • Glaucoma
• Congenital causes
  • Chronic blindness
• Autoimmune causes
  • CNS vasculitis, eg. Bickerstaff brainstem encephalitis
  • Optic neuritis due to MS
  • Cranial nerve neuropathy due to Miller-Fisher variant of  GBS
• Trauma
  • Bilateral eye trauma
  • Bilateral cataract repair
• Endocrine/metabolic pathology
  • Phaeochromocytoma
  • Hepatic encephalopathy
  • Wernicke's encephalopathy
  • Uraemic encephalpathy

In all honesty, one could not claim that bilateral prosthetic eyes are a valid member of a list of causes of bilaterally unreactive dilated pupils, because firstly why would anybody get a pair of prosthetic eyes with freakishly dilated pupils and secondly those aren't pupils.

Oh's Intensive Care manual: Chapter   51   (pp. 568)  Acute  cerebrovascular  complications by Bernard  Riley  and  Thearina  de  Beer. This chapter of Oh's has the distinction of having very few tables in it - there are only two, for an extremely long block of text.

Qureshi, Adnan I., et al. "Spontaneous intracerebral hemorrhage." New England Journal of Medicine 344.19 (2001): 1450-1460.

Caplan, L. R. "Basic Pathology, Anatomy, and Pathophysiology of Stroke." Caplan’s Stroke A Clinical Approach (2009): 23-4.

Walker, H. Kenneth, W. Dallas Hall, and J. Willis Hurst. "Clinical methods." 3rd edition.(1990). Chapter 63. Cranial Nerves IX and X: The Glossopharyngeal and Vagus Nerves- by Kenneth Walker

Rea, Paul. "Chapter 5: Hindbrain (Rhombencephalon)" Essential clinical anatomy of the nervous system. Academic Press, 2015.

Kühnlein, Peter, et al. "Diagnosis and treatment of bulbar symptoms in amyotrophic lateral sclerosis." Nature Reviews Neurology 4.7 (2008): 366.

Graham, P. J. "Congenital flaccid bulbar palsy." British medical journal 2.5400 (1964): 26.

Sang, Delia N., and Daniel M. Albert. "Retinoblastoma: clinical and histopathologic features." Human pathology 13.2 (1982): 133-147.

Sato, Hiromasa, Kosuke Naito, and Takao Hashimoto. "Acute isolated bilateral mydriasis: case reports and review of the literature." Case reports in neurology 6.1 (2014): 74-77.

Thomas, P. D. "The differential diagnosis of fixed dilated pupils: a case report and review." Critical Care and Resuscitation 2.1 (2000): 34.