Glucose metabolism with 18-FDG PET in 16 chronic migraineurs (mean age 42.5 +/- 11 years) with analgesic overuse, before and 3 weeks after medication withdrawal, was compared to controls. During use of medication, the cerebral areas including the orbitofrontal cortex (OFC) were hypometabolic, while the cerebellar vermis was hypermetabolic. After drug withdrawal, glucose uptake became almost normal, except the OFC that showed a further metabolic decrease. Most of the OFC hypometabolism was due to the overuse of combination analgesics and/or an ergotamine-caffeine preparation in 8 patients. 
COMMENT. Medication overuse headache is associated with persistent orbitofrontal (OFC) hypometabolism, while other cerebral areas show reversible metabolic changes. The authors speculate that hypoactivity in the OFC favors abuse of pain medication and predisposes the patient to relapse of medication overuse headache.
Analgesic overuse among adolescents with headache was studied in Norway from 1995-1997 (The Head-HUNT-Youth study) . The prevalence of daily analgesic overuse headache was 0.5%; in girls 0.8% and boys 0.2%. The association between analgesic use and daily headache occurred with all headache categories, but was most pronounced for migraine and less for tension-type headache. Analgesic use and headache frequency showed a significant linear relationship.