CLINICAL CORRESPONDENCE Paroxysmal hemicrania triggered by GTN

Chronic paroxysmal hemicrania (CPH) is one of a group of primary headaches disorders known as the trigeminal autonomic cephalgias (TACs) (1), which also includes the more common entity of cluster headache. These headaches share a number of clini-cal characteristics, such as their unilateral first and second division trigeminal pain and ipsilateral cranial autonomic activation. They also probably share pathophysiological similarities as demon-strated by recent functional imaging studies. Clinical differentiation between the two entities may be difficult because of the phenotypic overlap between them before a trial of medication (2, 3). This differ-ential diagnosis hinges on important and intriguing differences between them in their response to medi