Neurofibromatous Neuropathy: An Ultrastructural Study

Plexiform neurofibroma is pathognomonic of neurofibromatosis 1 (NF1). An NF1-associated peripheral neuropathy has been described in a small minority of NF1 patients but its histopathological features are poorly characterized. We report the case of a 46 years old woman presenting with bilateral sub-clavicular painful masses, without other stigmata of NF1. MRI showed bilateral plexiform lesions extending from cervical roots to the elbows. Nerve conduction studies documented a sensory-motor polyneuropathy. Morphometric analysis of sural nerve biopsy showed a preferential loss of large-caliber myelinated fibers with a g-ratio of 0.515, and the presence of regeneration clusters. By electron microscopy, marked and diffuse endoneurial fibrosis, with an altered relationship between Schwann cells (SC) and collagen fibrils, was observed. Moreover both myelinating and non-myelinating SC were characterized by the presence of various cell degradationproducts. These changes suggest that in neurofibromatous neuropathy, a widespread axonal atrophy and degeneration takes place independently on the presence of tumoral infiltration, possibly due to an impairment in SC-axon cross-talk. In this case, the co-existence of plexiform neurofibromas with a peripheral neuropathy, strongly suggests a diagnosis of NF1 even without fulfillment of clinical criteria. We propose that in the presence of plexiform neurofibromas, electrophysiological studies should be performed also in asymptomatic patients, in order to detect the existence of a subclinical neuropathy.