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. The study was part of a multifaceted, epidemiological study of different 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 frequency levels in migraine and tension-type headache. Chronic headache sufferers had higher amplitude values at rest in their temporal muscles than migraineurs, subjects with episodic tension-type headache and subjects without any experience of headache, probably due to insufficient relaxation. Frequency values during maximal voluntary contraction were decreased in chronic headache subjects and decreased with increasing frequency of headache in the previous year, indicating that chronic fatigue and/or changed fiber type composition exist in frequent headache sufferers. During experimental cold and pain stimulation no significant differences between headache subjects and the rest of the population were detected. Only subjects without any experience of headache had increased amplitude values during pain stimulation. No significant relation of amplitude values to frequency of tension-type headache or migraine in the previous 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 decreased in both the temporal and the frontal muscles during maximal voluntary contraction indicating submaximal contraction during pain. The present study supports the importance of peripheral factors such as increased fatigability, morphological, and/or metabolic changes in the pathogenesis of tension-type headache. However, the diagnostic value of EMG in migraine and tension-type headache is limited.