Stiff Person Syndrome
🧍♂️ About
- Stiff Person Syndrome (SPS): A rare autoimmune neurological disorder causing progressive muscle stiffness and spasms. Anti-GAD (glutamic acid decarboxylase) antibodies are commonly positive, supporting an autoimmune mechanism.
- Paraneoplastic Variant: Seen with cancers (esp. breast, lung), as part of broader paraneoplastic syndromes 🎗️.
🧬 Aetiology
- Role of GAD: Converts glutamate → GABA (main inhibitory neurotransmitter). In SPS, antibodies attack GAD → ↓ GABA → loss of inhibition → hyperexcitable neurons.
- In paraneoplastic forms, antibodies may target amphiphysin or other antigens.
⚠️ Clinical Features
- Typical Presentation: Middle-aged adults, slowly progressive.
- Muscle Stiffness: Axial muscles (back, trunk), leading to a stiff, “board-like” gait 🚶♂️.
- Painful Spasms: Triggered by stimuli (sudden touch, noise, stress) ⚡.
- Falls: Common due to stiffness and loss of postural reflexes → ↑ injury risk.
- Posture: Hyperlordosis or hyperextended posture may develop.
- Labile BP & Autonomic Symptoms: Due to autonomic involvement.
- Associated Autoimmunity: Up to 30% have type 1 diabetes; others include autoimmune thyroiditis, pernicious anaemia, vitiligo 🦠.
💡 Exam Pearl: Think SPS in a patient with progressive stiffness, falls, exaggerated startle response, and positive anti-GAD antibodies.
🧪 Investigations
- Antibody Testing: Anti-GAD65 (positive in ~60%); anti-amphiphysin in paraneoplastic cases.
- EMG: Continuous motor unit firing even at rest → hallmark finding.
- MRI Brain/Spine: Typically normal; helps exclude mimics (MS, structural lesions).
🩺 Management
- Immunomodulation:
- IVIG (first-line, strong evidence ✅)
- Plasmapheresis (if refractory)
- High-dose steroids
- Rituximab has been tried in resistant cases
- Symptomatic Treatment:
- Baclofen (GABAB agonist) → reduces rigidity
- Diazepam (benzodiazepine, GABAA agonist) → relieves spasms + anxiety
- Other options: Gabapentin, Tiagabine (GABAergic drugs)
- Paraneoplastic Forms: Treat underlying malignancy (surgery, chemo, immunotherapy) 🎗️.
- Supportive Care: Physiotherapy, occupational therapy, and fall prevention are essential.
📈 Prognosis
- Chronic course with gradual progression if untreated.
- Early immunotherapy + symptomatic treatment can stabilise symptoms and improve mobility.
- Falls and injury are major morbidity risks ⚠️.
📚 References
