Facial Onset Sensory and Motor Neuronopathy: A Case Series and Literature Review

Introduction: Facial Onset Sensory and Motor Neuronopathy (FOSMN) typically presents with paresthesias in the trigeminal nerve distribution and weakness that progresses rostro-caudally. Objective: To present two new cases of FOSMN, summarize the current literature, and address areas for future study. Methods: Observational data was collected from two patients with FOSMN from our institution. A literature review of FOSMN was completed using PubMed. Results: We identified 100 cases of FOSMN, including our two new cases. 93% presented with facial paresthesias. 97% had bulbar symptoms. Five had family history of ALS. Abnormal Blink reflex was most common on EMG/NCS. CSF was typically normal, but a rare severe case showed elevated protein. Mutations included: TARDBP, OPMD, D90A-SOD1, CHCHD10, VCP, and SQSTM1. Neuropathological studies showed neurodegenerative changes without inflammation. Some cases have reported transient stabilization or improvement to immunomodulatory therapy. Case Reports: A 72-year-old man presented with right-sided trigeminal paresthesias that progressed in a rostro-caudal fashion, dysphagia, and hand weakness. He died 4-5 years after symptom onset. A 69-year-old man presented with left-sided jaw paresthesias, dysphagia and dysarthria. He was trialed on IVIG for 1.5 years without improvement and died 2.6 years after symptom onset. Conclusion: FOSMN is a rare disorder with a unique clinical and electrophysiological phenotype. The pathophysiology has been associated with neurodegeneration and multiple gene mutations have correlated to FOSMN. Some reports suggest transient response to immunomodulatory therapy, though prospective studies are lacking. CSF protein elevation may be seen in severe disease. Future studies will help further elucidate the approach to diagnosis, treatment, and prognostic counseling (biomarkers).