Do the paroxysmal hemicranias differ pathophysiologically from cluster headache?
The PHs, like cluster headache, belong to a group of headache disorders known as the trigeminal autonomic cephalgias (TACs). The TACs are characterized by cyclical episodes of severe headaches that are associated with cranial autonomic activation. These disorders share a common pathophysiologic mechanism, the trigeminal autonomic reflex.
Like cluster headaches, the PH can be triggered by alcohol. Approximately 10% of patients with CPH report that attacks are precipitated either by bending or by rotating the head. Headache attacks may also be triggered by exerting external pressure against the transverse process of the C4 to C5, the C2 root, or the greater occipital nerve. Headaches may be precipitated within a few seconds of the trigger (range 5 to 60 seconds), sometimes in rapid succession without any refractory period.
Does it matter whether we call these headaches clusters or paroxysmal hemicranias?
Yes. The differential diagnosis is exceptionally important, as the PHs are often resistant to the medications that typically prevent cluster headaches. The PHs are uniquely responsive to treatment with indomethacin. In fact, the International Headache Society has deemed response to indomethacin therapy a sine qua non for establishing the diagnosis. Some headache specialists believe that there are patients with paroxysmal hemicrania refractory to indomethacin.