Introduction

Patients with spontaneous (non-traumatic) subarachnoid haemorrhage usually present first to their general practitioner. As general practitioners may see only a few cases during their career, subarachnoid haemorrhage can be a diagnostic and management challenge1; the incidence is about 8 per 100 000 per year.2 The condition accounts for 3% of patients presenting to emergency departments with headache3 and around 20 admissions per year to a general hospital covering 300 000 people. The prognosis remains poor: up to half of patients die and one third of survivors are left dependent.4 Early treatment can improve outcome5^–8; therefore prompt diagnosis and referral to a neuroscience unit is important.

How subarachnoid haemorrhage presents

Patients with subarachnoid haemorrhage usually present with a characteristic combination of symptoms (box 1). Sudden severe headache is the cardinal symptom, but it may be the only symptom in up to one third of patients with aneurysmal subarachnoid haemorrhage.12 When patients were asked how long it took for their headache to reach its maximum severity half of those with subarachnoid haemorrhage described it as instantaneous, one fifth said it developed over 1-5 minutes, and the rest said it escalated over more than five minutes.12 The headache usually persists for several days but may occasionally be much shorter. Even in the emergency department the positive predictive value of instantaneous severe headache for aneurysmal subarachnoid haemorrhage is only 39% (95% confidence interval 29% to 50%),12 so the speed of onset cannot be relied on to identify all cases of subarachnoid haemorrhage.

Although some believe that “sentinel bleeds” or “warning leaks” precede aneurysmal subarachnoid haemorrhage, the evidence is that headaches preceding the haemorrhage are rare and do not help in its diagnosis.14 Overestimation of the importance of sentinel bleeds arose from recall bias in hospital …