Abstract

FOSMN is heralded by facial sensory loss with subsequent sensory and motor loss spreading caudally. Few cases have been described in the literature but a single case with upper motor neurone features drew parallels to motor neurone disease (MND). A woman with FOSMN presented with facial sensory loss in 1998, aged 38. Cognitively normal she has developed worsening lower motor neurone weakness and sensory loss in her arms and then legs. She still walks with a frame. She has facial and neck flexion weakness. She has gradually lost her sensory action potentials and has developed neurogenic changes on EMG that spread caudally. Her horizontal saccades have recently become slowed (confirmed when quantified): vertical saccades normal, imputing dysfunction in the paramedian pontine reticular formation. Auto-immune profiles, lipids, lysosomal storage enzymes, genetics, neuro-axis MRI, muscle and nerve biopsy, cerebrospinal fluid, HIV and syphilis, protein electrophoresis, anti-neuronal antibodies have not revealed an alternative diagnosis. Relative sparing of eye movements early in the natural history of FOSMN draws further similarities to MND, recognised now to be predominately but not exclusively a motor degenerative disease. Post-mortem evidence is needed to establish the nosological place of FOSMN.