Most headache is migraine: this describes both the attack, and the underlying disorder. Most migraine is episodic and does not present to neurologists. Chronic headache is common, disabling, and frequently seen in neurological clinics. Chronic migraine (CM) was defined in 2004, revised in 2006. Some remain uncomfortable with the concept of CM. The question arises whether CM overlaps with tension-type headache (TTH) and with medication overuse headache (MOH). By definition, CM cannot be diagnosed in the presence of MOH; though the definition allows CM patients to have episodes of headache that transiently fulfil criteria for episodic migraine and for TTH. This study addresses the diagnosis of CM in a single neurologist's practice, where all patients since 1994 have been recorded on a database which was analysed for cases of CM over 5 years to 2010. Among 6264 total new patients, 2206 (35%) suffered headache. 363 (16%) had CM, of whom 310 (76%) had MOH. TTH was rarely diagnosed. The diagnosis of CM increased from 5% of all headache in 2006, to 34% in 2010. The latter figure is in line with data from other clinics. MOH so commonly overlaps with features of CM that it is unreasonable to make MOH an exclusion for CM diagnosis.
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