The purpose of this case series is to add to the growing literature on Facial Onset Sensory-Motor Neuronopathy (FOSMN) syndrome and explore early signs of this challenging diagnosis.

First described in 2006 as a novel syringomyelia-like syndrome, there are now at least 47 reported cases of FOSMN reported globally. FOSMN is thought to be a neurodegenerative syndrome that starts with sensory neuron loss in the trigeminal nerve distribution followed by rostral to caudal progression of sensory loss.  It often involves bulbar muscle weakness, with dysphagia and dysarthria, as well as facial muscle weakness. Cramps, fasciculations and upper extremity weakness tend to occur later in the disease course. Here, we describe two cases of FOSMN that were diagnosed at our institution and had varied disease progression.

A case series of two individuals with FOSMN is presented. We report the clinical, laboratory, imaging and neurophysiologic findings. Both patients were male and had symptom onset in their 6th decade of life. The first symptom was unilateral perioral numbness and paresthesias for both patients.  Sensory presentation varied markedly, with one having focal facial numbness, and the other having symptoms spreading to the scalp, neck, trunk and upper limbs. Bulbar involvement was seen early on and prominently in one patient while it was only minimal in the other. Electromyography showed active denervation in multiple muscle groups, reduced sensory nerve action potentials, and absent blink reflexes in both patients. MRI of the cervical spine showed cord atrophy. One patient was treated with IVIg but still progressed to PEG tube dependency, while the other did not receive treatment.

FOSMN syndrome is a challenging and rare syndrome.  Diagnosis depends on the characteristic clinical presentation of facial onset sensory loss and facial weakness in conjunction with electro- diagnostic testing showing sensory and motor neuronopathy, which is typically more severe rostrally, and exhibits absent or abnormal blink reflexes.