Stiff Person Syndrome Misdiagnosis: Clinical and Ancillary Testing Characteristics

Objective To assess stiff person syndrome (SPS) misdiagnosis and identify factors differentiating SPS from non-SPS. Background is a heterogeneous immune-mediated central hyperexcitability disorder that challenging to differentiate alternative diagnoses. Design/Methods Patients referred the Mayo Autoimmune Neurology Clinic for (01-Jul-2016 30-Jun-2021) were included. diagnosis was defined as compatible clinical confirmed by an autoimmune neurologist either serum positivity high-titer GAD65-IgG (>20.0 nmol/L), glycine-receptor-IgG or amphiphysin-IgG (seropositive cases), confirmatory electrodiagnostic studies (seronegative cases). Seven patients excluded (diagnostic uncertainty). compared presentation, examination findings, laboratory testing, treatment responses. Results Of 173 cases, 48 (28%) diagnosed with 125 (72%) Age sex did not significantly differ in two groups. Most seropositive (41/48 total: 27/41, 12/41 2/41). Fibromyalgia/chronic pain functional neurological most common non-SPS diagnoses (81/125, 65%). True more commonly had history of exaggerated startle (81% vs 56%, p = 0.02), unexplained falls (76% 46%, 0.001) prior autoimmunity (50% 27%, 0.005). On examination, often hypertonia (60% 24%, < 0.001), hyperreflexia (71% 43%, lumbar lordosis (67% 9%, but less likely signs (6% 33%, 0.001). abnormal (74% 17%, at least moderate symptomatic improvement benzodiazepines (51% 16%, immunotherapy (45% 13% Seventy-one received immunotherapy; only 4 condition. Conclusions non-neurologic. Misdiagnosis may be reduced considering paraclinical factors; improved diagnostic accuracy will reduce exposure unnecessary treatments health care costs.