An unusual cause of unilateral mydriasis
A 40 year old presented with a one day history of a dilated left pupil. She denied headaches, vomiting, nausea, eye pain or double vision. There was no history of topical eye drops or trauma. She had no significant past medical history and reported that she grew ornamental household flowers. On examination, her left pupil was dilated to 8mm compared to her right pupil at 3mm. The left pupil was non-reactive to both direct and consensual light responses and her accommodation reflex was impaired. Her right pupillary reflexes were intact. There was no ptosis and eye movements were unremarkable. Fundoscopy demonstrated no papilloedema. Her neurological examination was otherwise normal including deep tendon reflexes.
A sudden-onset fixed, dilated pupil resulting from compression of the third cranial nerve can be an ominous sign of life-threatening intracranial pathology. However, there were no other signs of a third nerve palsy. There were also no features of raised intracranial pressure. Therefore, it seemed that compression of the oculomotor nerve by pathology such as a posterior communicating artery aneurysm was unlikely. The absence of pain excluded acute closed angle glaucoma. Holmes Adie pupil tends to be a chronic condition, in contrast to the sudden-onset in our patient. She also denied any recent trauma, recent ophthalmology appointments or self-administered eye drops.
On further questioning she reported that she grew Angel’s trumpet, also known as Brugmansia, an ornamental plant grown for its bold, trumpet-shaped pendulous flowers. It contains parasympatholytic alkaloids such as atropine, hyoscyamine and scolopamine. There have been several previous reports of unilateral mydriasis caused by exposure to this plant. The underlying pharmacological mechanism is of blockage of the muscarinic receptors leading paralysis of the smooth muscle of the pupillary sphincter and ciliary muscles. Other systemic symptoms can include dry mouth, sweating, tachycardia, confusion and agitation.
Based upon the likelihood of exposure to this plant and the absence of other symptoms, a provisional diagnosis of mydriasis secondary to accidental Angel’s trumpet exposure was made. Our patient went on to have a magnetic resonance angiogram of the brain to exclude intracranial pathlogy. This was reported as normal, confirming our diagnosis, and her anisocoria went on to resolve completely after 72 hours.
The prevalence of physiological ansicoria is estimated at 19% in the general population. Chronic anisocoria with no other features is generally benign, whereas acute-onset anisocoria with other associated symptoms is more worrisome. Our case demonstrates the need for thorough history-taking & examination to first exclude the acute and potentially life-threatening causes before considering the wider differential diagnosis. This approach ensures patients safe management whilst in the emergency department. It also highlights the importance of considering exposure to environmental toxins as part of the differential diagnosis.
