Double discharges in neuromuscular diseases

Double discharges (doublets) of motor units were examined in routine EMG. The material consisted of 132 patients suffering from different neuromuscular diseases and 34 controls in whom the examined muscles were intact. Only m. tibialis anterior and biceps brachii were examined. Activity from at least 10 different motor units per muscle were recorded and analyzed off-line. Modified criteria were used in determining doubling units. Applying the modified criteria no doubling units were found in controls. In myopathies doublets occurred only in myotonic dystrophy and in one case of polymyositis in remission. In neuropathies, the occurrence of doublets was most common in proximal neuropathies. In polyneuropathies and root syndromes doubling units were relatively common, but none were found in exclusively distal neuropathies. It is concluded that doublets have a definite diagnostic value in routine EMG examination.