CIDP-like neuropathy in heterozygous C9orf72 mutation: a case report

Introduction: C9orf72 repeat expansion is usually associated with ALS, FTD and ALS/FTD overlap. We report an atypical neuromuscular presentation of C9orf72 repeat expansion. Case report: A 68-year-old patient developed a sensorimotor polyneuropathy with slow continuous worsening over three years. Symptoms started in the left foot and slowly extended to all four limbs. NCS were consistent with a non-length dependent predominantly axonal sensorimotor polyneuropathy, with some additional demyelinating features (proximal temporal dispersion and F wave latency prolongation). Electro-clinical presentation fulfilled EAN/PNS 2021 criteria for CIDP, but the patient was not responsive to IVIg. RT-PCR revealed a heterozygous pathogenic expansion of the C9orf72 gene. The patient’s father and brother died from ALS. At onset, his brother also had sensorimotor involvement and was misdiagnosed with CIDP. Discussion: This case may expand the phenotypic spectrum associated with C9orf72 repeat expansion. The initial phenotype could be a non-length-dependent sensory-motor polyneuropathy with demyelinating features that potentially mimics CIDP.