QUALITATIVELY ALTERED NOCICEPTION IN CHRONIC MYOFASCIAL PAIN

The aim of the present study was to investigate the stimulus-response function for pressure versus pain in patients with myofascial pain. Fo rty patients with chronic tension-type headache and 40 healthy control s were examined. Tenderness in 8 pericranial muscles and tendon insert ions was evaluated by manual palpation with a standardized evaluated m ethodology. Thereafter, a highly tender muscle and a largely normal mu scle were palpated with 7 different pressure intensities using a palpo meter, and the induced pain was recorded by the subjects on a visual a nalogue scale blinded for the observer. Pericranial myofascial tendern ess was considerably higher in patients than in controls (P < 0.00001) . The stimulus-response function recorded from normal muscle was well described by a power function. From highly tender muscle, the stimulus -response function was displaced towards lower pressures and, more imp ortantly, it was linear, i.e., qualitatively different from normal mus cle. Our results demonstrate for the first time that nociceptive proce sses are qualitatively altered in patients with chronic myofascial pai n and suggest that myofascial pain may be mediated by low-threshold me chanosensitive afferents projecting to sensitized dorsal horn neurons. Further investigations of these mechanisms may lead to an increased u nderstanding and better treatment of these common and often incapacita ting pain disorders.