Subarachnoid hemorrhage is a serious and life-threatening medical condition which commonly presents with an acute headache. Unfortunately, it remains frequently misdiagnosed at initial presentation with dire consequences in terms of patient morbidity and mortality. The goal of this paper is to review salient features in the clinical history, as well as recently developed clinical decision rules, which can help determine which patients warrant further investigation for subarachnoid hemorrhage when the initial presentation is that of an acute headache.A recent prospective observational study showed that occipital location, stabbing quality, presence of meningism, and onset of headache during exertion were characteristics in the clinical history that can distinguish the headache of SAH from other causes. The Ottawa headache rule is a clinical decision tool which was developed to help identify patients presenting to the ED with acute non-traumatic headache who require investigation to rule out subarachnoid hemorrhage. Using this tool, it is recommended that patients who meet any one of the following 6 criteria are investigated further: Onset greater than or equal to 40 years, presence of neck pain or stiffness, witnessed loss of consciousness, onset during exertion, thunder clap headache (pain peaking within 1 s), or limited neck flexion on exam. An informed and thoughtful approach that takes into account the timing, presentation, risk factors, and resources, as discussed here, should help distinguish between the patient that warrants further evaluation and intervention for SAH and one who does not. The Ottawa SAH rule is a useful clinical decision tool for young inexperienced clinicians in order to avoid missed diagnoses. However, its clinical value is limited by its low specificity. Clinical decision tools with higher specificity are needed.
