Stiff Person Syndrome (SPS) is a rare neurological disorder typically affecting adults, with infrequent cases reported in children and adolescents. The condition is characterized by the following clinical and pathophysiological features:

Clinical Features:

1. Progressive Rigidity and Muscle Spasms:

   • Predominantly involves the trunk and proximal limb muscles.
   • Muscle rigidity persists during wakefulness and is relieved during sleep.
   • Painful muscle spasms are common and can be spontaneous or triggered by external stimuli (e.g., sudden noise, touch, or emotional stress).

2. Sensitivity to External Stimuli:

   • Patients exhibit heightened sensitivity to environmental factors such as noise, touch, and emotional stress, which can exacerbate spasms and rigidity.

3. Electromyographic (EMG) Findings:

   • Continuous involuntary muscle fiber activity is observed in affected muscles, even at rest, which is pathognomonic for SPS.

Associations:

1. Autoimmune Links:

   • Strong association with diabetes mellitus and other autoimmune diseases (e.g., thyroiditis, vitiligo).
   • Up to 80% of patients have autoantibodies against glutamic acid decarboxylase (GAD), an enzyme found in GABAergic nerve terminals and pancreatic beta cells.

2. Paraneoplastic Syndromes:

   • In some cases, SPS may be associated with cancers, such as breast cancer, suggesting a paraneoplastic origin.

Diagnosis:

• Clinical assessment of rigidity and spasms.
• Serologic testing for GAD antibodies.
• EMG studies to confirm continuous muscle fiber activity.

Treatment:

1. Symptomatic Relief:

   • Benzodiazepines (e.g., diazepam) are the cornerstone of symptomatic management, helping to reduce muscle rigidity and spasms.
   • Baclofen, a GABA-B receptor agonist, may also provide relief.

2. Immunotherapy:

   • For longer-term control, immunomodulatory treatments are employed:
     • Plasma exchange.
     • Intravenous immunoglobulin (IVIG).
     • Immunosuppressive agents (e.g., corticosteroids, rituximab) in refractory cases.

3. Adjunctive Measures:

   • Physiotherapy to maintain muscle flexibility and prevent contractures.
   • Addressing underlying or associated autoimmune diseases.

Prognosis: While the disease often follows a chronic and progressive course, timely diagnosis and treatment with immunotherapy can improve symptoms and quality of life. Multidisciplinary care, including neurologists, immunologists, and physiotherapists, is essential for optimal management.