[A case of acute bilateral interosseous nerve palsy associated with severe hypopotassemia]

A 66-year-old housewife felt mild pains in both her forearms after wringing a floorcloth repeatedly while cleaning. The following day she was unable to extend her fingers, but could dorsiflex both wrists. A diagnosis of bilateral interosseous nerve palsy was made. Laboratory studies revealed severe hypopotassemia due to laxative abuse and mild rhabdomyolysis, but her general condition was almost good except for the nerve palsies. Nerve conduction studies suggested conduction disturbance of the posterior interosseous nerve in both forearms. Needle electromyography showed a myogenic pattern in all limbs and a neurogenic pattern only in the muscles innervated by the posterior interosseous nerve. As the serum potassium was normalized, she recovered rapidly from the palsies after only seven days. Repeated electrophysiological studies showed that the conduction disturbance and myogenic patterns had disappeared, and only the neurogenic pattern remained in the muscles innervated by the posterior interosseous nerve. The damage to the posterior interosseous nerve caused by repeated pronation and supination of the forearms when wringing a floorcloth was probably mild. However, hypokalemic neuromyopathy had probably already decreased the muscle membrane excitability, so severe palsy occurred following mild nerve damage. The correction of hypopotassemia alone achieved a dramatic improvement of the bilateral palsy because muscle excitability was restored. This rare case suggests that aggravation of entrapment neuropathy may occur due to hypokalemic neuromyopathy.