Facial onset sensory and motor neuronopathy: a diagnostic challenge

Facial onset sensory and motor neuronopathy (FOSMN) is a rare neurological disorder that combines features of both sensory neuropathy and motor neuron disease. Its clinical resemblance to trigeminal neuralgia and amyotrophic lateral sclerosis (ALS) often leads to delayed or incorrect diagnosis. Recent evidence suggests that FOSMN may represent a sensory-onset variant within the ALS spectrum, characterised by the addition of cranial and limb sensory involvement. The present report highlights this diagnostic challenge and emphasises that FOSMN can occur with prominent sensory symptoms and cranial nerve dysfunction even in the absence of significant bulbar features. Recognising this pattern broadens the classical understanding of motor neuron diseases, which are traditionally viewed as purely motor disorders. Awareness of such presentations and the use of targeted neurophysiological tests, particularly blink reflex studies, are essential for accurate diagnosis and better characterisation of this rare and evolving disease spectrum.