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Background
The development of unilateral mydriasis in a patient with cancer raises concerns for intracranial metastatic disease. We present a recognised but often overlooked cause of mydriasis caused by trandermal hyoscine hydrobromide.
Case presentation
A teenager with a diagnosis of Ewing's sarcoma of her right first rib with metastases to right iliac bone was commenced on a scopolamine patch (transdermal hyoscine) for cyclical nausea and vomiting related to chemotherapy (topotecan and cyclophosphamide). Previous trials of more conventional antiemetics (ondansetron and cyclizine) were unsuccessful largely due to tablet phobia and resultant non-compliance with oral medications. She was advised to apply a single patch behind her ear and replace every 72 h in keeping with the manufacturer's guidelines. Her symptoms improved rapidly and she was able to reduce the dose to a half patch within a month of commencing.
She presented to the oncology day ward 2 months later with acute onset visual disturbance. In particular she reported a 2-day history of an inability to focus up close which affected the right eye only. Distance vision was unaffected. She did not describe any pain, photophobia or diplopia. Examination of the eye revealed a unilateral dilated pupil which was reactive to light but sluggish compared with the left pupil. A complete clinical neurological examination revealed no other findings. There were no other antimuscarinic effects reported (including dry mouth, constipation, urinary retention, flushing or cardiac effects).
Differential diagnosis
The patient refused the oncology team's proposal of a CT brain to outrule metastases.
Treatment
Patch removal was advised, which led to symptom resolution after several days.
Outcome and follow-up
Nausea did not re-occur, as chemotherapy was subsequently discontinued due to progression of disease locally, and she remained symptom free until death 2 months later.
Discussion
Hyoscine hydrobromide is a belladonna alkaloid and antimuscarinic agent which has similar actions to atropine. 1 Its action on the iris, ciliary body and certain secretory glands is more potent than atropine while its actions on cardiac, intestinal and bronchial smooth muscle are less potent.
Transdermal hyoscine is applied to the postauricular area and contains a drug reservoir of 1.5 mg of hyoscine....