Abstract

Although subclinical involvement of sensory neurons in amyotrophic lateral sclerosis (ALS) has been previously demonstrated, corneal small fiber sensory neuropathy has not been reported to-date. We examined a group of sporadic ALS patients with corneal confocal microscopy, a recently developed imaging technique allowing in vivo observation of corneal small sensory fibers. Corneal confocal microscopy (CCM) examination revealed a reduction of corneal small fiber sensory nerve number and branching in ALS patients. Quantitative analysis demonstrated an increase in tortuosity and reduction in length and fractal dimension of ALS patients’ corneal nerve fibers compared to age-matched controls. Moreover, bulbar function disability scores were significantly related to measures of corneal nerve fibers anatomical damage. Our study demonstrates for the first time a corneal small fiber sensory neuropathy in ALS patients. This finding further suggests a link between sporadic ALS and facial-onset sensory and motor neuronopathy (FOSMN) syndrome, a rare condition characterized by early sensory symptoms (with trigeminal nerve distribution), followed by wasting and weakness of bulbar and upper limb muscles. In addition, the finding supports a model of neurodegeneration in ALS as a focally advancing process.

Highlights

  • Amyotrophic lateral sclerosis (ALS) is a fatal disorder primarily characterized by progressive degeneration of upper (UMN) and lower motor neurons (LMN), in the brain and spinal cord (Riva et al, 2011)

  • We examined a group of sporadic ALS patients with corneal confocal microscopy, a recently developed imaging technique allowing in vivo observation of corneal small sensory fibers

  • Corneal confocal microscopy examination revealed a reduction of corneal small fiber sensory nerve number and branching in ALS patients

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Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is a fatal disorder primarily characterized by progressive degeneration of upper (UMN) and lower motor neurons (LMN), in the brain and spinal cord (Riva et al, 2011). Despite the fact that a modest age-related decrease of skin nerve fiber density has been observed in both healthy controls and ALS patients (Lauria et al, 2010; Weis et al, 2011), subclinical involvement of sensory neurons in the neuro-degenerative process has been independently demonstrated by previous clinical and pathologic studies (Kawamura et al, 1981; Heads et al, 1991; Hammad et al, 2007; Weis et al, 2011). The aim of this study was to examine a group of sporadic ALS patients with corneal confocal microscopy (CCM), a recently developed imaging technique allowing in vivo observation of corneal small sensory fibers. Corneal confocal microscopy has a number of comparative advantages over previous techniques such as skin biopsy, allowing non invasive, potentially repeatable and quantitative analysis of small sensory fibers at the microscopic level (Ferrari et al, 2010)

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