(HealthDay)—The use of 15 headache days/month as a threshold to distinguish episodic and chronic migraine does not capture the burden of illness, according to a study recently published online in Headache.

Ryotaro Ishii, M.D., Ph.D., from the Mayo Clinic in Phoenix, and colleagues assessed whether the 15-day threshold of headache days per month adequately reflects substantial differences in disability across the full spectrum of migraine. The analysis included 836 individuals with migraine participating in the American Registry for Migraine Research.

The researchers observed significant relationships with increasing disability, lost productive time, and pain interference in higher headache frequency categories. For participants with eight to 14 headache days/month (180) compared with those with 15 to 23 headache days/month (153), there were no significant differences for most measures, including pain intensity or interference and work productivity and activity impairment. The two groups did significantly differ for disability. Patients with zero to seven headache days/month (286) had significantly lower disability and work productivity and activity impairment than all other groups, while those with ≥24 headache days/month (217) had significantly worse disability and work productivity and activity impairment versus all other groups.

“These results have important implications for future refinements in the classification of migraine,” the authors write.

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