Indomethacin responsive headache syndromes: chronic paroxysmal hemicrania and Hemicrania continua. How they were discovered and what we have learned since.

In the indomethacin responsive headaches (IRHs), chronic paroxysmal hemicrania (CPH) and Hemicrania continua (HC), the indomethacin (INDO) response is swift, absolute, and permanent, with moderate doses. Traditionally, CPH has been linked to cluster headache (CH) due to clinical similarities: unilaterality, intensity, and some autonomic phenomena. However, other clinical features differ essentially between these two headaches: sex ratio, mean attack frequency (CPH: 13.6 versus CH: 1.7 attacks/day), and duration of attacks. The therapeutic profile in CPH (indomethacin effect: ++; triptan effect: generally non-existent) is reversed in CH. The autonomic phenomena also differ clearly, a forehead supersensitivity sweating pattern and Horner-like pupil being present only in CH. The chronic/non-chronic stage ratio is 3.9 in CPH, against 0.14 in CH, a >25 times difference. Conversely, CPH and HC are very similar, clinically speaking. Accordingly, we should probably sever the link between CH and CPH and favour, instead, a linking together of CPH and HC, the two principal IRHs.