What is hemicrania continua?

In the absence of a secondary headache disorder, hemicrania continua is a constant, one-sided headache associated with at least one of the following: eye redness or watering on the same side of the pain, congested or runny nostril on the same side of the pain, swollen eyelid on the same side of the pain, facial/forehead sweating on the same side of the pain, smaller pupil or drooping eyelid on the same side of the pain, a sense of restlessness or agitation, or aggravation of the headache by movement. 

The headache is present for at least three months with exacerbations of moderate to severe intensity. Migrainous symptoms such as light sensitivity and sound sensitivity are often seen in hemicrania continua which can potentially lead to a misdiagnosis of migraine. 

Hemicrania continua is treated successfully by a non-steroidal anti-inflammatory drug (NSAID) called indomethacin.