Facial onset sensory and motor neuronopathy (FOSMN) is a rare and slowly progressive motor neuron disorder. Affected people initially experience facial tingling and numbness which eventually spread to the scalp, neck, upper trunk and upper limbs. These sensory abnormalities are later followed by the onset of motor symptoms such as cramps, muscle twitches, difficulty swallowing, dysarthria, muscle weakness and atrophy. The hallmark of FOSMN is a reduced or absent corneal reflex (the reflex to blink when something touches the eye). The underlying cause is currently unknown. Most cases appear to occur sporadically in people with no family history of the condition. Although there is no consensus regarding the best treatment options for FOSMN, some affected people have temporary improvement in response to intravenous immunoglobulin or plasmapheresis.

Studies have also shown that SOD1 and OPMD genes may play a role in FOSMN; however, the specific association is unclear. Although there are currently no familial cases of FOSMN reported in the medical literature, some scientists suspect that newer genetic testing technologies may uncover additional genetic factors.

There is currently no evidence to suggest that facial onset sensory and motor neuronopathy is inherited. To date, no familial cases have been reported which means that the condition appears to occur sporadically in people with no family history of the condition.

Signs and symptoms of facial onset sensory and motor neuronopathy (FOSMN) generally become apparent by age 54 (range 38-77 years) and vary significantly from person to person. The earliest symptoms include facial tingling and numbness which eventually spread to the scalp, neck, upper trunk and upper limbs. These sensory abnormalities often present months to years prior to the development of motor symptoms such as cramps, muscle twitches, difficulty swallowing, dysarthria, muscle weakness and atrophy. The hallmark of FOSMN is the reduced or absence of the corneal reflex (the reflex to blink when something touches the eye).

Due to the rarity of the condition, the best approach for effective treatment is currently unclear. Several treatments have been mentioned in case reports including intravenous immunoglobulin (IVIG), plasmapheresis (PE), corticosteroids, azathioprine, mycophenolate mofetil, and rituximab. Although some patients showed temporary improvements with IVIG and PE, the majority of cases did not respond to any of these treatments.