Solitary plexiform neurofibroma presenting as purely motor axonal cervical plexopathy

Abstract

A 27‐year‐old male presented with three years of progressive weakness and atrophy in his right arm. He did not have sensory complaints or pain but occasional proximal arm dysesthesias. Neurological examination showed severe right shoulder girdle atrophy and proximal limb weakness affecting muscles supplied by the fifth and sixth cervical roots. Strength was normal distally in the right arm and in the other limbs. Deep tendon reflexes were normal. Sensation was normal. Laboratory studies showed increased creatine kinase levels. Anti‐GM1 IgM antibodies were not found. Electrodiagnostic studies were consistent with either focal motor neuronopathy or right brachial plexopathy involving the upper trunk. Nerve conduction studies did not show conduction blocks or slow conduction velocity. The CMAP amplitude of the right median nerve was normal. EMG showed chronic denervation and fibrillation potentials in paraspinal and arm muscles innervated by right C5–C6. MRI studies revealed markedly increased signal intensity on T2‐weighted images of the fifth and sixth right cervical roots and upper trunk of right plexus with contrast‐enhanced T1‐weighted images. A provisional diagnosis of motor axonal inflammatory plexopathy was made based on the purely motor focal deficit, increased creatine kinase levels and enhancing focal hypertrophic roots on MRI, as described in CIDP and MMN. The patient was treated with high dose IVIg 2 g/Kg over four days with no improvement. Two months later a biopsy of enlarged cervical root revealed a plexiform neurofibroma. The patient did not have a family history or other typical abnormalities of neurofibromatosis (NF1), including cafè‐au‐lait spots, skin fold freckling, Lisch nodules in the iris and bone dysplasia. Solitary plexiform neurofibroma may occur in patients without other stigmata of NF1 and should be considered in the differential diagnosis of purely motor focal inflammatory radiculoplexopathy.