Facial Onset Sensorimotor Neuronopathy Syndrome: A Case Series

Objective:

Facial onset sensorimotor neuronopathy (FOSMN) is a recently described neurological syndrome characterized by slow onset of facial sensory abnormalities and subsequent development of motor deficits. Except for 1 patient, FOSMN has so far been identified only in men.

Methods:

We describe a case series of 3 women with FOSMN. We report their clinical, laboratory, and neurophysiological findings.

Results:

The age of onset ranged from 39 to 72 years (mean, 60 years) with presentation 4–7 years after symptom onset. The first symptom was slowly progressive facial numbness, which was followed years later by dysphagia and impaired corneal reflexes. Dysarthria occurred in 2 patients, and mild arm weakness was noted in 2. Muscle stretch reflexes were increased in 1 patient, and in another case, arm sensation was reduced. Laboratory studies were unremarkable, and magnetic resonance imaging of the brain in 3 patients and of the cervical spine in 2 patients was normal. Nerve conduction studies showed reduced leg compound muscle action potential amplitudes in 1 patient and asymmetrically reduced arm sensory nerve action potentials in another case. In 2 patients, electromyography showed widespread active denervation in arm muscles in conjunction with the involvement of leg muscles in 1 case and the tongue in the other patient. We identified chronic neurogenic motor unit action potentials in the genioglossus muscle of all 3 cases while facial EMG performed in case 3 showed similar findings. Blink reflexes were abnormal in all patients. We treated 1 patient with high-dose intravenous methylprednisolone followed by intravenous immunoglobulin without any improvement, and she required percutaneous endoscopic gastrostomy (PEG) tube placement.

Conclusions:

This is the first case series describing 3 women with the FOSMN syndrome. We expand phenotype of FOSMN to include upper motor neuron signs and normal arm sensory nerve action potentials.

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