SY2.3. Evaluation of dystonia

Abstract

Dystonia is a syndrome characterized by sustained or intermittent muscle contractions causing abnormal, often repetitive, movements, postures, or both. It can be primary or secondary and the patient can present with pure dystonia or dystonia along with other movement disorders such as tremor, myoclonus, parkinsonism, etc. Evaluation of a patient presenting primarily with dystonia includes detailed clinical evaluation, haematologic and neurometabolic work up, imaging and neurophysiological/ electrophysiological studies. This presentation will focus on the electrophysiological evaluation of dystonia, which helps in understanding the pathophysiology and better characterization of the abnormal movement. Compared to tremor and myoclonus, electrophysiological evaluation of muscle spasms and dystonia is difficult. The first step is recording surface EMG from the involved muscles for prolonged periods during abnormal movements (dystonia), rest, and with voluntary contraction. The agonists and antagonists should be included to detect co-contraction, and the unaffected muscles of the same or opposite limbs should also be studied to document overflow dystonia if present. During EMG evaluation, patients are also asked to perform various tasks which can induce dystonia, such as mental arithmetic, finger tapping and opening and closing fist of the unaffected hand, writing (in patients with writer’s cramp). EMG is analyzed to determine: (i) the pattern of EMG activity in agonists and antagonists during dystonia (spasm) (ii) duration of each EMG burst (iii) the regularity of occurrence of EMG bursts, (iv) presence of overflow activity in remote muscles while performing discrete voluntary acts, and (v) the difference in the degree of EMG activity (area of rectified EMG) between epochs with and without muscle spasms. Other investigations which are often useful to characterize dystonia or a dystonic syndrome include: (i) H-reflex recovery curve (ii) mechanically and electrically induced long-latency muscle stretch reflex (iii) reciprocal inhibition between antagonistic muscles (iv) brainstem reflexes such as blink reflex (v) cortical SEP (vi) Bereitschaftpotential (BP) and Contingent negative variation (CNV) and (viii) transcranial magnetic stimulation (TMS). TMS specifically helps to study the excitatory and inhibitory changes in the brain in patients with dystonia and may also be a useful tool to monitor therapeutic interventions.