The decision to investigate a patient for SAH rests largely on the history. The requirement to fully evaluate patients with reduced consciousness or a focal neurological deficit presents little difficulty. The challenge is greatest in patients with milder symptoms who are neurologically pristine . Misdiagnosis in this group results in increased morbidity and mortality in those who have most to benefit from timely treatment.
The question of which ED patients with acute headache and a normal neurological examination should proceed to investigation for exclusion of SAH has led to initial work in Canada on the development of clinical decision rules. These are highly sensitive for the detection of SAH in patients with certain specific clinical characteristics but are not yet generalisable [30,39,40].
Studies have shown the misdiagnosis rate of SAH over the past 30 years to be in excess of 10% [8,9]. Three reasons for misdiagnosis recur repeatedly [41,42]:
- Failure to consider the diagnosis of SAH
- Failure to obtain and correctly interpret the results of a CT brain scan
- Failure to perform and correctly interpret the results of a lumbar puncture (LP)
The diagnosis of SAH should be considered in all patients presenting with first or worst headache, particularly of sudden onset. Failure to entertain this possibility is still a regular cause of medical mishap.
Failure to consider and properly investigate patients with a suspected SAH is still a significant cause of medical error .