Facial Onset Sensory and Motor Neuronopathy: New Cases, Cognitive Changes, and Pathophysiology

Abstract

Purpose of review: To improve our clinical understanding of facial onset sensory and motor neuronopathy (FOSMN).

Recent findings: We identified 29 new cases and 71 literature cases, resulting in a cohort of 100 patients with FOSMN. During follow-up, cognitive and behavioral changes became apparent in 8 patients, suggesting that changes within the spectrum of frontotemporal dementia (FTD) are a part of the natural history of FOSMN. Another new finding was chorea, seen in 6 cases. Despite reports of autoantibodies, there is no consistent evidence to suggest an autoimmune pathogenesis. Four of 6 autopsies had TAR DNA-binding protein (TDP) 43 pathology. Seven cases had genetic mutations associated with neurodegenerative diseases.

Summary: FOSMN is a rare disease with a highly characteristic onset and pattern of disease progression involving initial sensory disturbances, followed by bulbar weakness with a cranial to caudal spread of pathology. Although not conclusive, the balance of evidence suggests that FOSMN is most likely to be a TDP-43 proteinopathy within the amyotrophic lateral sclerosis-FTD spectrum.

Figure 1. Summary of the Results from the Literature Search

The search was performed on September 1, 2019, using PubMed and EMBASE on articles from January 1, 2006, to September 1, 2019, reporting on FOSMN. Titles and abstracts were screened, and relevant full-text articles were retrieved. References were screened for additional studies. FOSMN = facial onset sensory and motor neuronopathy.

Figure 2. Summary Distribution Abnormalities in FOSMN

Distribution of sensory, motor, and electrophysiologic findings in patients with FOSMN. In all 3 pictures, the darker color represents the higher amount of patients with abnormalities, showing the cranial-caudal spreading. EMG = electromyography; FOSMN = facial onset sensory and motor neuronopathy; SNAP = sensory nerve action potential.