The clinical features of headache with subarachnoid hemorrhage (SAH) are distinct from those associated with other headache syndromes, according to the first study of its type that examined in detail the clinical characteristics of the presenting headache in SAH. Researchers enrolled patients through the emergency department and from the neurosciences intensive care unit, and documented clinical features of the headache including the time to peak intensity, location, associated symptoms, and activities that caused worsening. 158 subjects were enrolled, of whom 20 patients had SAH and 138 did not. They found:

• Notable distinguishing features on history included occipital location (55% in the SAH group vs 22% in the non-SAH group), “stabbing” quality (35% in the SAH group vs 5% in the non-SAH group), presence of prior headache (50% in the SAH group vs 83% in the non-SAH group), and associated meningismus (80% in the SAH group and 42% in the non-SAH group).
• 65% of patients with SAH reported that their headache peaked within 1 second of onset, compared with only 10% of those without SAH.