Table 2 Proposed diagnostic criteria for thunderclap headache attributed to idiopathic reversible cerebral vasoconstriction (THARCV) syndrome

A. At least one headache attack with the following characteristics

     1. Abrupt and explosive headache

     2. Severe

B. Presence of reversible intracranial arterial narrowing

C. No association with conditions such as

     1. Vascular malformation, aneurysm, subarachnoid hemorrhage, CNS vasculitis or trauma

     2. Pheochromocytoma, systemic vasculitis

     3. Use of illicit drugs or other known vasoactive (constrictor) substances

     4. Pregnancy, post-partum or eclampsia