Objective:

To characterize the clinical, radiological and electrophysiological features of an atypical phenotype of neurofibromatosis type 1 (NF1) presenting with bilateral multiple schwannomas spanning the entire spinal cord, mimicking length-dependent polyneuropathy.

Background:

NF1 is an autosomal dominant disorder caused by NF1 gene mutation. While neurofibromas are the hallmark lesion of NF1, schwannomas are typically associated with NF2 or schwannomatosis, rarely reported in NF1. This atypical anatomical distribution mimicking polyneuropathy poses significant diagnostic challenges.

Design/Methods:

NA

Results:

A 36-year-old male with no significant personal or family history, presented with a six-year history of progressive neuropathic pain, distal muscle weakness, and unsteady gait. Neurological examination revealed length-dependent sensorimotor polyneuropathy characterized by Medical Research Council (MRC) grade 3/5 distal weakness and amyotrophy, stocking-glove hypoesthesia and paresthesia, with areflexia. Nerve conduction study and electromyography confirmed severe axonal sensorimotor polyneuropathy with partial denervation. However, dermatological inspection identified >6 cutaneous café-au-lait macules with axillary freckling but no cutaneous neurofibromas. Slit-lamp examination revealed bilateral Lisch nodules. These findings fulfilled the 2021 revised NIH diagnostic criteria for NF1 and the diagnosis was established with exclusion of other etiologies of acquired polyneuropathy.

Neuroimaging using MRI revealed bilateral vestibular schwannomas associated to diffuse, bilateral T2-hyperintense, homogeneously gadolinium-enhancing tumors at each intervertebral foramen from C2 to L5, radiologically consistent with plexiform schwannomas, without peripheral nerves abnormalities.

This case mimicking a length-dependent polyneuropathy, fulfills the NF1 diagnostic criteria, yet presents diffuse spinal plexiform schwannomas associated with vestibular involvement typically present in schwannomatosis.

Conclusions:

This case underscores a novel NF1 phenotype where extensive spinal schwannomas mimic length-dependent polyneuropathy. This phenotype broadens the clinical and radiological spectrum of NF1, blurs the diagnostic boundaries between NF1 and schwannomatosis, and highlights the importance of comprehensive neuroaxis imaging and genetic analysis in atypical cases.