Stiff-Person Syndrome: Diagnostic and Therapeutic Insights Into a Rare Autoimmune Neurological Disorder

Stiff-person syndrome (SPS) is a rare autoimmune neurological disorder that is frequently underrecognized due to overlapping musculoskeletal and neuropsychiatric symptoms, leading to delays in diagnosis. We report a 56-year-old Moroccan woman with a seven-year history of progressive lumbar stiffness and painful, stimulus-sensitive spasms extending to both lower limbs, resulting in marked functional limitation and falls. Serum testing showed markedly elevated anti-glutamic acid decarboxylase (anti-GAD) antibodies (greater than 20,000 U/mL), while the spine MRI revealed only mild degenerative changes, and whole-body positron emission tomography excluded malignancy. Symptomatic therapy with pregabalin and baclofen provided partial relief. Intravenous immunoglobulin was administered at a total dose of 2 g/kg over five days, yielding a substantial reduction in stiffness and spasm frequency; at one month, she demonstrated improved mobility and greater independence. Rituximab was proposed for long-term disease control given disease severity and seropositivity. This case underscores the diagnostic value of anti-GAD testing when imaging is unrevealing and highlights that timely initiation of immunotherapy, together with symptomatic agents and rehabilitation, can meaningfully improve outcomes. A multidisciplinary strategy is essential for sustained functional recovery and quality of life in SPS.