A 38-year-old woman presented to the emergency department with recurrent severe headaches. Although initial computer tomography (CT) brain imaging was unremarkable, a later CT venogram demonstrated a small subarachnoid haemorrhage. Magnetic resonance angiogram (MRA) brain imaging subsequently confirmed reversible cerebral vasoconstriction syndrome (RCVS). In the acute setting, RCVS rarely falls into a differential diagnosis for headache presentations, as in this case. The radiological

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... y can make diagnosis of RCVS challenging. However, there are clinical consistencies that can aid physicians into accurately diagnosing RCVS. A thorough history, including a medication history, can help identify potential triggers of RCVS. As in this case, the combination of commonly used drugs, including antihistamines, provides a plausible trigger for RCVS. The direct vasoactive role of antihistamines is unclear, yet there is suggestion for its ability to potentiate the vasoactive action of other drugs. In this case we propose a causal relationship between the use of antihistamine and the development of RCVS.