To outline the role of diagnostic criteria, antibody interpretation, and ancillary testing in reducing SPS misdiagnosis and avoiding unnecessary treatments.

Misdiagnosis of Stiff-Person Syndrome Disorder (SPSD) occurs three times more often than accurate diagnosis often due to misinterpretation of antibody results, clinical signs, or lack of supplementary studies such as other antibody testing, cerebrospinal fluid analysis and electrodiagnostic studies. Although GAD65-IgG is commonly found in SPSD patients, it can also be found in those with type 1 diabetes, autoimmune conditions, or in healthy individuals at low titers.

None of the patients fulfilled the diagnostic criteria for SPDS. Each had a history of other autoimmune disorders, including multiple sclerosis, hashimoto's thyroiditis, systemic lupus erythematous, myasthenia gravis, and sjögren’s syndrome. The symptoms varied and included painful muscle spasms, numbness, paresthesias, leg weakness, tremors, wide-based/unsteady gait, cognitive changes, dysphagia, and fatigue.  There was a lack of objective rigidity, truncal stiffness, hyper lordosis, hyperreflexia, or episodic spasms triggered by startle on exam.  For all patients the serum GAD-65 antibodies were weakly positive. Only one patient underwent an electromyography, which yielded normal results, and only one had a lumbar puncture resulting in normal cerebrospinal fluid. No additional antibodies were tested.  Four patients were treated with monthly IVIG for 1-3 years, with one developing transfusion-associated circulatory overload.

Over-reliance on weakly positive GAD-65 antibodies led to misdiagnosis of SPSD in all cases. While patients reported muscle spasms, none had objective findings on exam.  Additional clinical and ancillary testing can help minimize SPSD misdiagnosis and exposure to unnecessary treatments.