Hemicrania continua is a chronic headache. It is part of a group of primary headache disorders known as trigeminal autonomic cephalgias. The headache in hemicrania continua is unilateral and constant; however, periods of exacerbation lasting several hours to days typically occur on a weekly or monthly basis. Pain is typically located periorbitally or temporally and is mild or moderate in intensity but can become severe during exacerbations. The headache is typically throbbing, but patients may also experience brief stabbing pains. There are often associated ipsilateral autonomic symptoms during periods of exacerbations including ptosis, miosis, lacrimation, conjunctival injection, eyelid swelling, facial sweating, nasal congestion, or rhinorrhea. Migrainous features may accompany the headache.

For most patients with hemicrania continua, the headache will persist for life without appropriate preventive treatment. Hemicrania continua is absolutely responsive to indomethacin, and lack of response suggests an alternative diagnosis.

There are 2 subclasses of hemicrania continua: the remitting subtype and the unremitting subtype. Patients with the remitting subtype typically experience periods of remission of headache lasting at least 24 hours in duration. In the unremitting subtype, the headache is continuous for at least 1 year without remission periods. The majority of patients have the unremitting subtype.

Hemicrania continua is a rare condition, with approximately 100 cases reported worldwide. The disorder is more common in women, with an estimated female to male ratio of 1.8 to 1. The mean age at onset is in the 30s; however, it has also been diagnosed in children and elderly individuals.