RESUMO
Background: It is unknown if medication-overuse headache, clinically similar to chronic tension-type headache, has pre-attentive problems which may be related to pain or substance abuse. Methods: Auditory frequency deviance elicited mismatch negativity was recorded from 22 patients with chronic tension-type headache, 26 with medication-overuse headache from underlying chronic tension-type headache and 41 healthy volunteers as controls. Their depression and anxiety scores were noted. Results: There were no signifi cant differences in the N1 latency or amplitude to both standard and deviant stimuli for the different groups. However, the latency and amplitude of mismatch negativity were signifi cantly shortened and reduced at Fz, Cz, and Pz in medication-overuse headache as compared to chronic tension-type headache and normal subjects. Anxiety levels were elevated in chronic tensiontype headache and medication-overuse headache subjects compared to healthy controls but were not correlated with mismatch negativity latency or amplitude in a given group. Conclusions: In medication-overuse headache subjects, the shortened mismatch negativity latency indicates quick involuntary attention switching to auditory change, while its reduced amplitude indicates poor accuracy in discriminating early stimuli, which may be related to medication overuse rather than to the head pain experienced.