Mismatch negativity in chronic tension-type headache with and without medication-overuse

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. Neurology Asia 2013; 18(2) : 183 – 189 Address correspondence to: Dr. Wei WANG, B.Med., D.Sc., Department of Clinical Psychology and Psychiatry, Zhejiang University School of Medicine, Yuhangtang Road 866, Hangzhou, Zhejiang 310058, China; Tel: +86-571-88208188. Email: [email protected], [email protected] INTRODUCTION The population-based one-year prevalence of the medication-overuse headache (MOH) ranges between 0.7 to 1.7% in different countries. In terms of its frequency, intensity and duration, MOH behaves more like chronic tension-type headache (CTTH) than chronic migraine. Underlying mechanisms of the preexisting headache e.g. migraine or CTTH may contribute to the pathogenesis of MOH. In CTTH, these include both peripheral (e.g. altered myofascial nociception) and central (e.g. inadequate endogenous pain control) mechanisms while in migraine, there is activation of trigeminovascular system and initiation of cortical spreading depression. However, the exact pathophysiology of MOH, especially when evolved from tensiontype headache, is not well-understood, with central sensitization and defi cits of endogenous pain control suspected of playing a role. Moreover, MOH has been assumed to be a type of addiction disorder and its mechanisms may overlap with those that contribute to the drug addiction. Neuropsychological studies in migraine have shown various attention defi cits in both adult and childhood migraine with and without aura. On the other hand, there is also a study which showed no attention defi cits in children and adolescents with migraine or tension-type headache. Up to now, there has been no study showing altered attention in MOH. However, other chronic pain disorders such as the rheumatoid arthritis or fi bromyalgia have been shown to have impaired selective attention. Drug abusers also have been found to have defi cits in cognitive fl exibility and working memory. Neurophysiological studies using a cerebral cognitive index, the event-related potential (ERP) P3, have been carried out in migraine and CTTH. For example, reduced P3 amplitude through an active auditory discriminative task was found in migraine and in CTTH, and reduced P3 amplitude through a passive auditory paradigm was also found in migraine and CTTH. In addition, the active auditory P3 amplitude was found to be deformed in chronic pain sufferers, Neurology Asia June 2013 184 and the active visual P3 amplitude was reduced in substance-abuse disorders. There has been no study showing P3 changes in MOH. Another ERP component, the mismatch negativity (MMN), which occurs approximately 100-250 ms after the onset of a deviant stimulus, acts as an index of involuntary pre-attention, or an involuntary shift of attention. MMN latency indicates the speed of involuntary attention switching to stimulus change while its amplitude indicates the extent of allocation of neural resources to pre-attentive process of a stimulus change. MMN was found to be reduced in amplitude in migraine and CTTH. Whether or not the MMN morphology is intact in MOH still opens to question. However, MMN amplitude was decreased, and its latency was delayed in chronic pain sufferers. In addition, many studies have shown that MMN was reduced or delayed in addiction disorders. The purpose of the present study was to look for pre-attentive problems in MOH. Based on the previous reports, we hypothesize that MMN would be delayed and reduced in this headache type. However, due to the heterogeneity of MOH, we decided to include only patients whose MOH evolved from CTTH and compared them with patients with CTTH but without MOH. As there is high prevalence of anxiety and depression in MOH and CTTH, anxiety and depression levels were measured in all our study subjects.