Clinical Neurophysiological Study for the Diagnosis of Functional Cranial-Cervical Dystonia.

Objectives: The differential diagnosis of functional and other etiologies of dystonia can be difficult. We performed a clinical neurophysiological study in a female patient with cranial-cervical dystonia, providing strong evidence for the diagnosis of functional dystonia.

Methods: The patient had torticollis and intermittent facial pulling with downward deviation of the left angle of the mouth. She had left laterocollis and right torticollis with left shoulder elevation. She additionally experienced limited anterior-posterior flexion of the neck and moderate limitation of lateral flexion and neck rotation in both directions without spinal cord compression. We recorded abnormal discrete movements of the lower lip with surface electromyography (EMG). Electroencephalography was recorded simultaneously to identify a possible Bereitschaftspotential (BP) before the abnormal movement. We also tested inhibition of the blink reflex and pre-pulse inhibition (PPI) using supraorbital nerve stimulation with a conditioning-test paired-pulse paradigm.

Results: The EMG of the dystonic left lip movements varied in shape, duration, and amplitude. A BP was observed before the abnormal lip movement. The topographic distribution of BP with abnormal lip movement was similar to that with voluntarily mimicked lip movement and with voluntary movement of arm extension. The R2 component of the blink reflex was inhibited with a preceding conditioning pulse at interstimulus intervals of 150-1000 ms. Significant PPI was found at intervals of 60-120 ms. The R1 component of the blink reflex was not inhibited.

Discussion: The patient has functional dystonia. Our results suggest that in some circumstances clinical neurophysiological tests can support the differential diagnosis of functional cranial-cervical dystonia.