QUANTITATIVE SURFACE EMG OF PERICRANIAL MUSCLES IN HEADACHE - A POPULATION STUDY

Quantitative EMG from the right frontal and both temporal muscles was studied in 547 adults randomly selected from the general population. T he study was part of a multifaceted, epidemiological study of differen t headache disorders. Surface EMG was recorded by an observer blinded to the persons' history of headache, previous illness and mental state . The present study provides data on amplitude and mean and median fre quency levels in migraine and tension-type headache. Chronic headache sufferers had higher amplitude values at rest in their temporal muscle s than migraineurs, subjects with episodic tension-type headache and s ubjects without any experience of headache, probably due to insufficie nt relaxation. Frequency values during maximal voluntary contraction w ere decreased in chronic headache subjects and decreased with increasi ng frequency of headache in the previous year, indicating that chronic fatigue and/or changed fiber type composition exist in frequent heada che sufferers. During experimental cold and pain stimulation no signif icant differences between headache subjects and the rest of the popula tion were detected. Only subjects without any experience of headache h ad increased amplitude values during pain stimulation. No significant relation of amplitude values to frequency of tension-type headache or migraine in the pervious year was detected. In 66 subjects with actual headache amplitude values were increased in the frontal muscle during rest indicating increased tension. Moreover, amplitude values were de creased in both the temporal and the frontal muscles during maximal vo luntary contraction indicating submaximal contraction during pain. The present study supports the importance of peripheral factors such as i ncreased fatigability, morphological, and/or metabolic changes in the pathogenesis of tension-type headache. However, the diagnostic value o f EMG in migraine and tension-type headache is limited.