G.P.241: Muscle histopathology in late-onset spinal muscular atrophies differs from c9orf72-related-ALS

Abstract

Muscle biopsy findings in amyotrophic lateral sclerosis (ALS) patients have been described in several publications, but the cohorts have been etiologically heterogeneous. Our aim was to assess myopathological differences between three genetically defined motor neuron disease entities. We analyzed all muscle biopsies of c9ORF72-related ALS (c9ALS) patients performed at our unit and compared them with biopsies of patients with benign hereditary lower motor neuron disorders (Late-onset spinal motor neuronopathy, LOSMoN and spinobulbar muscular atrophy, SBMA). We found the fiber type grouping of also normal sized type IIA (2A by ATPase) fibers to be very specific to the late-onset spinal muscular atrophy (LOSMoN/SBMA) cohort, whereas in c9ALS patients, type IIA fiber groups were always markedly atrophic. Severely atrophic rounded type IIA fibers, scattered or in groups, were significantly more common in LOSMoN/SBMA than c9ALS. Small group atrophy consisting of fast and slow fibers were more common in c9ALS than in LOSMoN/SBMA. According to our results, muscle biopsy may be a useful additional diagnostic tool in suspected motor neuron diseases.