[Needle electromyography in the thoracic paraspinal muscles of motor neuron disease]

Usefulness of needle electromyography (EMG) in the thoracic paraspinal muscles was investigated in 22 patients with amyotrophic lateral sclerosis (ALS). All patients revealed denervation changes in the thoracic paraspinal muscles, though the EMG findings were insufficient to fulfill the WFN criteria of lower motor neuron sign. We could not diagnose three patients as having ALS at their first visits by conventional EMG. One patient had restricted neurogenic change within one limb and two patients had cervical spondylosis causing difficulty to diagnose anterior horn cell involvement at the cervical level. In these patients, however, we believed to having ALS because of the neurogenic findings of EMG in the thoracic paraspinal muscles. Afterwards, they became clinically definite ALS. On relation to respiratory function, patients with acute denervation potentials (fibrillation potentials) in upper thoracic paraspinal muscles innervated by Th1 approximately Th4 had respiratory dysfunction (% VC is less than 80). Two patients had the acute denervation potentials in the upper thoracic paraspinal muscles before the decrease in % VC. We conclude that needle EMG testing in thoracic paraspinal muscle is useful to diagnose ALS in early stage and to predict respiratory failure in ALS patients.