Coma and small pupils

(NB. Causes labeled with an asterisk* generally only cause small pupils, a coexistent cause of of coma would need to be present)

The differential diagnosis of coma with small pupils includes:

Non-toxicological causes

• Pontine lesions (infarct or hemorrhage)
  classically involves sudden collapse with coma, pinpoint pupils and a spastic tetraparesis with brisk reflexes.
• Metabolic encephalopathy
  associated acute or chronic systemic illness, spontaneous roving eye movements
  [see Neurological Mind-boggler 007]
• Bilateral Horner’s syndrome*
  central (e.g. massive thalamic or supra-thalamic lesions, lateral brainstem lesions), pre-ganglionic (e.g Pancoast tumour), post-ganglionic (e.g. neck trauma, carotid artery dissection, cluster headaches)
• Senile miosis*
• Argyll-Robertson pupils*
  small, irregular, fixed pupil with little response to atropine and acts like a prostitute – ‘accommodates but doesn’t react’… to light.
  nearly pathognomonic of neurosyphillis
• Pseudo-Argyll Robinson pupils* (more likely to be mid-sized)
  diabetes mellitus
  any chronic lesion of the rostral midbrain (e.g. multiple sclerosis, encephalitis, Lyme disease, pinealoma, syringobulbia, chronic alcoholism)
• Holmes-Adie pupils* (constrictive phase)
  [See Ophthalmological Befuddler 001]

Toxicological causes

• Sedatives

opioids
clonidine
barbiturates
chloral hydrate
GHB

• Antipsychotics

phenothiazines (eg. chlorpromazaine)
atypicals (olanzepine, quetiapine, clozapine)

• Cholinergic agents

acetylcholinesterase inhibitors

organophosphates
carbamates
nerve agents (e.g. sarin)

Alzheimers dementia agents* – e.g. donezepil, tacrine
Myasthenia gravis agents* – eostigmine, physostigmine, edrophonium

Acetylcholine agonists

muscarinic agents – pilocarpine (eye drops)*
nicotine
mushrooms

• Other drugs

valproate
phenoxybenzamine (alpha blocker)
beta blocker eye drops*

Hopefully the naloxone works, eh.