List three causes of coma with bilateral miosis. (30% marks)
• Pontine lesions
• Thalamic haemorrhage
• Metabolic encephalopathy
• Organophosphate toxicity
• Other cholinergic agents (e.g. donezepil for Alzheimers) Opioids, barbituates, GHB, clonidine
• Mushroom intoxication (cholinergic effect)
This question is virtually identical to Question 21.1 from the second paper of 2015, except this time the causes of coma are each worth 10% of the marks instead of 5%.
In summary, a list of causes would resemble the following:
Causes of bilaterally small pupils which do not produce coma:
The whole "metabolic encephalopathy" thing is somewhat vague, and is included here because it is technically accurate. Metabolic encephalopathy can describe many things, and produce many signs.
A reader of LITFL had also pointed out that phenothiazines should be expected to cause mydriasis, by virtue of their anticholinergic effect. This is not the case. A 1973 article from California Medicinereports 48 cases of phenothiazine poisoning, in which the pupils were almost invariably small. This can be attributed to the alpha-antagonist effects of these drugs, which override the anticholinergic effects.
Specifically, the reader is directed to Coma and Small Pupils, aka Neurological Mind-boggler 002
Barry, Daniel, Frank L. Meyskens Jr, and Charles E. Becker. "Phenothiazine Poisoning A Review of 48 Cases." California medicine 118.1 (1973): 1.