Role of nitric oxide in cluster headache.

Nitric oxide (NO) is an important molecule in headache pathophysiology. NO regulates vascular tone and acts as a potent vasodilator, and thus participates in regulating blood flow. NO is also considered to play a role in processing sensory information and pain sensitization. In this article, we review the role of NO in one of the primary headache disorders, cluster headache (CH). The pathophysiology of CH is still not completely understood. A multifactorial genesis where NO is likely to be involved is probable. The level of NO production has been shown to correlate with disease activity in several inflammatory disorders, such as cystitis, multiple sclerosis, and cerebral lupus erythematosus. In this article, the issue of whether similar circumstances apply for CH and also the role of NO in the pathophysiology of CH in a wider perspective are discussed.