[A case of neurofibromatosis type 2 (NF2) presenting with late-onset axonal polyneuropathy]

The patient was a 69-year-old man who had a two-year history of slowly-progressive gait disturbance, paresthesia of the distal legs and bilateral hearing impairment. Nerve conduction study showed symmetric motor-dominant axonal polyneuropathy of the legs. Gadolinium-enhanced brain and spinal cord MRI revealed bilateral vestibular schwannomas, and multiple small schwannomas in the cauda equina, the surface of spinal cord and lumbar muscles. Genetic examination disclosed a point mutation in the exon 2 (T161C: L54P) of the neurofibromatosis 2 (NF2) gene, and the diagnosis of NF2 was made. It has been reported that axonal polyneuropathy is frequently observed in patients with NF2. Therefore, it is possible that axonal polyneuropathy of the present patient may be due to the abnormality of the NF2 gene, but not to the direct compression of the tumors, because the localization of his schwannomas in the cauda equina and the spinal cord could not explain his symmetric polyneuropathy. Although this patient showed no characteristic clinical manifestations such as cutaneous lesions, gadolinium-enhanced brain and spinal cord MRI was useful for the detection of asymptomatic schwannomas. NF2 should be considered as a differential diagnosis in patients with axonal polyneuropathy, even if it is late-onset.