A case of multiple sclerosis (MS) in a woman with hereditary facioscapulohumeral muscular dystrophy (FSHD). 

The coexistence of MS and FSHD is a rare occurrence. To date, only 4 case reports describing the coexistence of MS and FSHD have been published. As distinct neurological disorders with different pathophysiological mechanisms, their overlap can complicate diagnosis and management.

A 35 y/o woman with genetically confirmed FSHD with baseline facial, upper and lower extremity weakness and mildly progressive disease course presented in June 2025 to the emergency department with 4-5 days of acute worsening facial weakness and diplopia. Her history includes diabetes mellitus (s/p pancreatectomy for hyperinsulinism at the age of 8) and a paternal history of FSHD. Her neurological exam was significant for restricted horizontal eye movements bilaterally, impaired convergence, improving facial weakness, decreased sensation to light touch and pinprick in the left lower extremity, and otherwise baseline neurological exam. Her new sensory and visual exam findings with acute presentation were thought unlikely to be FSHD, so an MRI brain and spine with contrast was obtained, which revealed multiple scattered T2 hyperintense lesions in the periventricular and subcortical/juxtacortical white matter, central medulla, left anterolateral aspect of the pons, right thalamus and insula. Her medullary lesion showed diffusion restriction on DWI sequence, implying subacute development. MRI spine had small T2 hyperintense lesions in the cervical cord at C4-C5 and within the conus at T12-L1, concerning for demyelinating lesions. Based on her new neurological symptoms, signs and imaging findings, she was diagnosed with MS. 

This case emphasizes that in patients with FSHD, the appearance of new or rapidly evolving neurological symptoms that do not conform to the natural course of the myopathy should raise suspicion for an additional process such as MS.