Objective: We describe a rare case of a young woman with an immune-mediated movement disorder (paraneoplastic Stiff Person Syndrome) associated with a mediastinal liposarcoma. This case highlights existing clinical knowledge gaps in this area and the importance of early treatment initiation for improved clinical outcomes.

Background: Stiff-Person Syndrome (SPS) is a disabling disorder in which there is near continuous contraction of agonist and antagonist muscles caused by involuntary motor-unit firing at rest. 85% of SPS cases are idiopathic and associated antibodies include those of GAD 65 antibodies. The paraneoplastic form of SPS can be associated with amiphysin antibodies and tumors commonly associated are small-cell lung cancer, breast cancer and rarely thymoma. Treatment includes immunomodulatory agents.

Method: NA

Results: A 21-year-old female with vitiligo was evaluated for 3 months of of seizure-like episodes. Episodes consisted of tonic stiffening and frequent excruciating back spasms; aggravated by stress and alleviated by rest and benzodiazepines. She also reported a 30-pound weight loss. Her symptoms were progressive and began to impede independent ambulation thus prompting her visit. On neurologic exam she demonstrated marked weakness in the hip flexor muscles and slow wide based gait with reduced hip and knee flexion. Given the phenomenology of the episodes, a diagnosis of SPS was considered. Pertinent laboratory work up revealed elevated anti-GAD antibody titre (1:4800). Paraneoplastic panel was negative for amphiphysin antibody but positive for striated muscle antibodies. Neuroaxis imaging was normal. Malignancy work up revealed a mediastinal mass. She underwent resection of massive anterior mediastinal mass and a total thymectomy. Histopathologic evaluation revealed a well-differentiated liposarcoma. Subsequently, the patient received 5 days of plasmapheresis. 8 months post-surgery, she continues to report substantial improvement in her symptoms, denies any new episodes and is now able to ambulate independently again.

Conclusion: This case represents a unique presentation of a liposarcoma in a patient with SPS given her younger age group and diagnosis of atypical mediastinal liposarcoma. Immune-mediated movement disorders associated with soft-tissue tumors are rarely identified in literature. Her recovery highlights the utility of early and aggressive initiation of treatment for improved clinical and functional outcomes.

References: 1. Alexopoulos, H, Marinos C. “Immunology of stiff person syndrome and other GAD-associated neurological disorders.” Expert review of clinical immunology (2013): 1043-1053.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/immune-mediated-movement-disorder-as-a-rare-manifestation-of-a-sarcoma/