Clinical features of FOSMN syndrome in Korea: A comparative analysis with bulbar-onset amyotrophic lateral sclerosis.

Facial onset sensory and motor neuronopathy (FOSMN) syndrome is a rare neurodegenerative disorder initially characterized by facial sensory deficits, which later progress to motor deficits in a rostral-caudal distribution. This study investigated the prevalence, clinical features, and prognosis of FOSMN syndrome and compared these aspects with those of bulbar-onset amyotrophic lateral sclerosis (ALS) within a single institutional cohort of motor neuron diseases. We identified four patients with FOSMN syndrome who had been misclassified as having bulbar-onset ALS, representing approximately 2 % of such ALS cases. The median age of onset for FOSMN syndrome was similar to that of bulbar-onset ALS. However, patients with FOSMN syndrome were often diagnosed at more advanced stages and had lower ALS Functional Rating Scale-revised (ALSFRS-R) scores. Despite the slower progression of FOSMN syndrome, therapeutic interventions such as gastrostomy or non-invasive ventilation were frequently required. In conclusion, this study provides detailed clinical profiles of patients with FOSMN syndrome and deepens our understanding of a heterogeneous group of neurodegenerative disorders.