PAIN PERCEPTION IN IDIOPATHIC CERVICAL DYSTONIA (SPASMODIC TORTICOLLIS)

Cervical spinal pain is frequently found in conjunction with idiopathi c cervical dystonia (ICD), a focal dystonia characterized by sustained deviation of the head. Since the perception of noxious stimuli has ne ver been studied in ICD, we performed a controlled study to obtain mor e insight into the psychophysics of dystonia-related muscle pain by ev aluating pressure-induced pain levels. In nine ICD patients and five g ender- and age-matched asymptomatic control subjects, pain-pressure th resholds (PPTs) were determined in the stemocleidomastoid and upper tr apezius muscles, both at resting activity and at maximal voluntary con traction (MVC). The masseter muscles served as non-pathological contro l regions. To determine the accuracy of PPT values, pain intensity and unpleasantness were rated at threshold on 100-mm visual analogue scal es. Four replication measurements were obtained. The data were analyze d by multilevel procedures. For all muscles under investigation, avera ge PPTs of the ICD patients were about two times lower than those of t he control subjects (P < 0.001-0.0005) and showed a smaller intra-subj ect variance. Further, average PPTs at MVC were about two times higher than those at resting activity (P < 0.005). These results provide psy chophysical evidence to suggest that, at controlled levels of muscle c ontraction, the threshold of pain perception is decreased in ICD. In a ddition, ICD patients seem to be better able to establish their own PP Ts than control subjects, which might be due to a different setting of the discriminative aspect of pain in ICD. Surprisingly, lower intensi ty and unpleasantness scores were found in ICD patients with coincidin g painful and deviated sides than in ICD patients for whom the painful side was opposite to the deviated one (P < 0.05). This finding might be of clinical importance for defining functional disability and predi cting treatment outcome.