The Canadian study by Perry et al just published in the BMJ studied 3132 patients with worst ever headache across 11 ED’s between 2000-2009 of which 240 (7.7%) had subarachnoid haemorrhage.
CT scanning overall had a sensitivity of 93% for detecting SAH, but if done within 6 hours of onset of headache and interpreted by an experienced radiologist, the sensitivity rose to 100% picking up ALL 121 patients with SAH of the 953 patients scanned within 6 hours.
Looks like its time to modify our practices as long as we have access to experienced radiologists – overnight may be an issue when such access may not be readily available.
Their related study (see pdf here) trying to develop a Canadian SAH rule of who to do a CT scan upon needs further validation but suggests that consideration for possible SAH and thus possible CT scan on all patients with sudden onset headache (reaching peak intensity within 1 hour of onset), which has not occurred more than twice over the past 6 months (thus excluding chronic recurrent headache patients), who have any of the following features:
- age >= 40 years
- witnessed LOC
- complaint of neck pain or neck stiffness
- onset with exertion
- arrival by ambulance
- diastolic BP >= 100mmHg
- systolic BP >= 160mmHg
Of the patients included in their study, 54% had benign headache, 27% migraine, 6.5% SAH, 4.3% viral, 1.8% TIA, and 1.5% had post-coital headache.
They used 3 rules using variable items above, and each of the rules had 100% sensitivity for SAH, while specificity ranged from 28-39%
It will be interesting to see how the validation studies pan out.