Abstract

Background: Stiff-Person Syndrome (SPS) is a rare autoimmune neurological disorder. Historically estimated at 1–2 per million, more recent population-based data suggest the prevalence may be higher (up to ~2 per 100,000 in one U.S. health-system study). Characterized by progressive axial rigidity, painful stimulus-triggered spasms, and continuous motor unit activity on electromyography, SPS remains critically underrecognized. Diagnostic delays are common and contribute to preventable morbidity, including falls, fractures, and loss of independence. Case presentation: We report the case of a 63-year-old gentleman who presented with progressive axial stiffness over several months, beginning in his trunk and spreading to his proximal limbs. He experienced excruciating spasms triggered by minimal tactile stimuli and emotional stress. Examination revealed profound axial rigidity with a hyperlordotic gait. Electromyography demonstrated the pathognomonic pattern of continuous motor unit activity with co-contraction of agonist and antagonist muscles. Serum testing confirmed high-titer anti-glutamic acid decarboxylase 65 (GAD65) antibodies (>10,000 IU/mL). Key mimics including tetanus, parkinsonism, and neuromyotonia were systematically excluded. Management and outcome: The patient was managed through two simultaneous therapeutic pathways: symptom control (diazepam, baclofen, gabapentin, and environmental modification) and immune modulation. Because corticosteroids can destabilize glycemic control in a population with a high prevalence of type 1 diabetes, immunotherapy was planned with intravenous immunoglobulin (IVIG) as the preferred agent, with corticosteroids used cautiously and with glucose monitoring. The patient demonstrated steady, significant improvement in rigidity and spasm frequency, with enhanced functional mobility at discharge. Discussion: This case underscores several critical clinical principles: (1) the diagnosis of SPS is primarily clinical—the phenotype combined with EMG findings constitutes the definitive diagnostic tool; (2) prompt recognition and initiation of treatment, including benzodiazepines, baclofen, and immunotherapy, can dramatically improve prognosis; and (3) multidisciplinary coordination between neurology, rehabilitation medicine, and critical care is essential for optimal outcomes. Conclusion: SPS is rare but highly recognizable when clinicians maintain a high index of suspicion. Early diagnosis, confirmed by EMG, and timely immune-targeted therapy are the keys to improving prognosis and restoring independence in this chronic, complex disorder.

Keywords

Stiff-Person Syndrome, anti-GAD65 antibodies, continuous motor unit activity, intravenous immunoglobulin, neuro-rehabilitation, autoimmune neurology