Abstract
Facial-onset sensory and motor neuronopathy (FOSMN) is a rare, progressive neurodegenerative disorder characterized by sensory loss and motor deficits, primarily affecting the face and upper extremities. The condition begins with sensory impairments in the trigeminal nerve distribution, extending to involve the scalp, neck, upper limbs, and trunk. Symptoms include facial weakness, bulbar disturbances (dysphonia, dysarthria, dysphagia, and sialorrhea), and lower motor neuron signs (weakness, atrophy, fasciculation, and cramps) in the limbs. A hallmark of FOSMN is the diminished or absent corneal reflex, indicating trigeminal nerve involvement and leading to potential complications like neurotrophic keratitis (NK), which can cause corneal ulceration and blindness. The etiology of FOSMN remains uncertain, with theories proposing autoimmune or neurodegenerative origins. Diagnosis is challenging due to the overlap with other ocular surface disorders, necessitating careful examination and differential diagnosis. Management focuses on symptomatic relief, including eye protection to prevent corneal complications. Awareness and early detection of ocular symptoms in FOSMN are crucial for preventing severe outcomes like NK and blindness.