Cluster headache, hypothalamus, and orexin.

Cluster headache (CH) is a highly disabling condition resulting in severe, recurrent unilateral bouts of pain and accompanying autonomic symptoms. This review describes some current views regarding the underlying pathophysiology covering the pain and cranial autonomic (parasympathetic) activation, and highlights the potential importance of the hypothalamus in CH. The hypothalamus is known to modulate many functions and has been shown to be involved in the pathophysiology of a variety of primary headaches, including CH. Hypothalamic structures are likely to underlie the circadian and circannual periodicity of attacks and contribute to the pain and autonomic disturbances. We discuss the hypothalamic involvement in CH and modulation of trigeminovascular processing and examine the emerging involvement of the hypothalamic orexinergic system as a possible key pathway in CH pathophysiology.