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In April 2009, a 47-year-old woman with a history of diabetes mellitus type II, hypertension and asthma presented to hospital following an episode of transient loss of consciousness and headache. She had felt briefly dizzy beforehand, and was witnessed to be unconscious for a few minutes, during which there was generalised stiffness and some jerking of her limbs. On regaining consciousness she complained of a severe headache with nausea and vomiting which was still present on arrival at hospital, but there were no other symptoms. She was an ex-smoker and tee-total, and there was no family history of neurological disease. On examination she was fully conscious, with no neurological deficit apart from longstanding left amblyopia.
What is the differential diagnosis and what are the most appropriate initial investigations?
The differential diagnoses of a sudden onset headache are listed in the table. All patients presenting with a sudden onset headache, maximal at onset or within a few minutes and lasting longer than an hour, should be considered as subarachnoid haemorrhage (SAH) until proven otherwise. Only investigations can reliably differentiate benign primary causes from less benign secondary causes; the most appropriate firstline investigation is a CT scan of the head, as well as baseline blood tests.1 If this confirms SAH, then ideally one should proceed directly to CT angiography to identify any underlying vascular abnormality.
A CT in this case revealed subarachnoid blood in the left cerebral sulci as well as in the parafalcine and right Sylvian fissures (figure 1). She was diagnosed with a grade I SAH and transferred to our unit. Routine blood tests were unremarkable except for a white cell count of 15.5×109/l (normal 4–11).
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