Hemicrania continua is considered a primary headache disorder, meaning that it's not caused by another condition. It's a rare but treatable disorder. According to the International Headache Society's (IHS) International Classification of Headache Disorders, 2nd Edition, hemicrania continua is a "persistent strictly unilateral headache responsive to indomethacin."

The IHS diagnostic criteria for hemicrania continua is:

1. Headache for more than 3 months fulfilling criteria B–D
2. All of the following characteristics:
   1. unilateral pain without side-shift
   2. daily and continuous, without pain-free periods
   3. moderate intensity, but with exacerbations of severe pain
3. At least one of the following autonomic features occurs during exacerbations and ipsilateral to the side of pain:
   1. conjunctival injection and/or lacrimation
   2. nasal congestion and/or rhinorrhoea
   3. ptosis and/or miosis
4. Complete response to therapeutic doses of indomethacinNot attributed to another disorder

Hemicrania continua usually presents a mild to moderate daily headache. However, along with the daily, one-sided headache, it also causes exacerbations of more severe headache, which occurs on the same side as the daily headache and is characteristic of Migraine pain. These more severe episodes can last from 45 minutes to days. During these exacerbations, symptoms of other disorders may be present:

1. Migraine symptoms:
   1. throbbing pain
   2. nausea and/or vomiting
   3. phonophobia
   4. photophobia
2. Cluster headache symptoms:
   1. conjunctival injection and/or lacrimation
   2. nasal congestion and/or rhinorrhoea
   3. ptosis and/or miosis

The factor that allows hemicrania continua and its exacerbations to be differentiated from Migraine attacks and cluster headaches is that hemicrania continua is completely responsive to indomethacin. Triptans and other abortive medications do not affect hemicrania continua.

The cause of hemicrania continua is unknown. As with Migraine disease and many other headache disorders, there is no definitive diagnostic test for hemicrania continua. Tests such as an MRI may be performed to rule out other causes for the headache. When a patient has the symptoms of hemicrania continua, it's considered "diagnostic" if they respond completely to indomethacin.

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Resources:

International Headache Society. International Classification of Headache Disorders, 2nd Edition.

Tepper, Stewart J., M.D. "Understanding Migraine and Other Headaches." University Press of Mississippi. 2004.

Young, William B., M.D.; Silberstein, Stephen D., M.D. "Migraine and Other Headaches." American Academy of Neurology Press. 2004.

Evans, Randolph W.; Mathew, Ninan T. "Handbook of Headache," Second Edition. Lippincott Williams & Wilkins. 2005.

Published January 17, 2005.