Chronic Daily Headache - A Reappraisal

Chronic Daily Headache (CDH) generally refers to frequent headache occuring more than 15 days/month for over three months. Such headaches may be primary or secondary - the latter referring to headaches related to identifiable intra and extracranial vascular or other pathologies or systemic illnesses. The primary type may be subclassified as short and long lasting ones, depending upon whether the headache spells are more or less than four hours in duration. The present review would deal with the four major types of long lasting primary CDH which include Chronic migraine (CM), Chronic tension type headache (CTTH), New daily persistent headache (NDPH) and Hemicrania continua (HC). The first part of the article would focus on the clinical pattern recognising features of these types. The relationship of medication overuse to CM would be critically evaluated. In the second part, the status of CDH in the recently proposed classification of headache disorders by the International Headache Society would be briefly evaluated. In the next section the clinical Profile or CDH in Indian patients would be highlighted based on available published data. Lastly, the pathophysiology of this vexing condition would be discussed specially in relation to CM and postulating on how it may evolve from episodic migraine