[Significance of flexed posture and neck instability as a cause of chronic muscle contraction headache].

Cause of a muscle contraction headache (MCH) is due to sustained contraction of the neck and head muscles. This is proved by the effect of local anesthesia and EMG findings. However, the pathophysiology of abnormal muscle contraction is still unclear. Also, there is no explanation about female's greater susceptibility to MCH. The purpose of our report is to study the mechanism of abnormal muscle contraction and to find out a way to prevent it. We have examined 826 (572 female & 254 male) patients with MCH using EMG and dynamic X-ray. Results are most of MCH patients have a tendency to bend their head downward at the onset of headache. EMG shows continuous discharge of the posterior neck muscles so long as they keep this posture. Once they look up, however, EMG discharge usually subsides. Therefore, these muscle contraction are not involuntary, but passive as the results of drooping head. In 12 patients, severe attack of MCH were temporarily alleviated by the local anesthesia to the suboccipital tender point. In patients complaining MCH of one side, they often have a tendency to bend their neck toward the opposite direction, thus contracting the painful side of the neck muscles. It is also found that looking up to make orbito-meatal line more than 10 degrees from horizontal plane is enough to minimize muscle contraction, and to prevent or alleviate headache. Not all people experience headache, though.(ABSTRACT TRUNCATED AT 250 WORDS)