Is LP indicated for patients with recurrent thunderclap headaches over a 4-week period and negative head imaging for SAH?

I think this depends on what kind of head imaging was done to rule out SAH. If the patient has had a totally normal head MRI and MRA (not only ruling out SAH, aneurysm but also RCVS), then LP is warranted to insure there is no inflammatory or infectious component as a cause for the headache. I think it is also important to make sure that the diagnosis of thunderclap headache is correct. Thunderclap headache is not the worse headache of your life but rather a severe headache that escalates to full severity in a matter of 1-2 minutes.

Such benign presentation (recurrent thunderclap headaches only) may have been RCVS but the diagnosis may have been missed. Spasm peaks around 10 days after headache onset. When arterial imaging is done too early or too late, arterial spasm and specific RCVS diagnosis might be missed. CTA, MRA, and angiogram also differ in sensitivity.

After 4 weeks, however, headache should also be dissipating in RCVS. If the thunderclap headaches are occurring after a month without improvement in pattern, I would consider an alternate diagnosis.

RCVS2 score was developed to distinguish intracranial arteriopathy trying to distinguish RCVS from other stenoses such as vasculitis and atherosclerosis. In the absence of arterial stenosis, how the score should b...