Stiff person spectrum disorders: An illustrative case series of their phenotypic and antibody diversity.

Stiff person spectrum disorders (SPSD) are a broad group of immune-mediated disorders. Clinical presentations include classical stiff person syndrome (SPS), focal SPS, and progressive encephalomyelitis with rigidity and myoclonus (PERM). The most frequently associated antibodies are anti-GAD65, anti-GlyR, anti-amphiphysin, and anti-DPPX. Immunotherapy is the primary treatment modality. We present an illustrative case series of three patients: anti-GlyR antibody-mediated PERM presenting as rapidly progressive dementia; anti-amphiphysin antibody-mediated SPS; and SPS presentation with anti-Zic4 antibodies, spasmodic laryngeal stridor and fluctuating eyelid ptosis. Clinical characteristics, CSF findings, neurophysiological features, adequate immunological assays and a high suspicion index are essential for prompt diagnosis and management.