[Neuralgic amyotrophy or an isolated lesion of the anterior interosseal nerve?]

In this article we describe five patients with acute or subacute weakness of flexor pollicis longus and flexor digitorum profundus. A possible diagnosis of an isolated lesion (entrapment) of the anterior interosseus nerve was considered. However, clinical and neurophysiological findings suggested a diagnosis of neuralgic amyotrophy. Three patients experienced acute shoulder pain at the onset. Sensory loss at the base of the thumb was observed in two patients, and two patients were affected bilaterally. All patients had EMG signs of involvement outside the anterior interosseus nerve innervation area. Low amplitude sensory action potentials were observed in three patients. One patient was operated upon and entrapment was not observed during surgery. Reinnervation was not seen after five months, but was noted in three patients who were investigated 13, 13.5, and 30.5 months after the onset. Thus, the prognosis in this unusual form of neuralgic amyotrophy seems to be rather good, and the length of time before reinnervation supports the theory that the site of the lesion must be located proximally, e.g. in the brachial plexus.