Glutamic acid decarboxylase (GAD) antibody-positive paraneoplastic stiff person syndrome associated with mediastinal liposarcoma.

Stiff person syndrome (SPS) is a rare, debilitating neurological illness characterised by rigidity and spasms of the axial muscles, causing severe restrictions to mobility. SPS can be classic, partial or paraneoplastic. We report a case of a young woman who presented with seizures and painful spasms of the thoracolumbar muscles who was subsequently diagnosed with SPS. Serological work revealed glutamic acid decarboxylase (GAD) antibodies and imaging showed a large mediastinal mass. The patient underwent surgical resection of the mediastinal mass and final pathology revealed well-differentiated mediastinal liposarcoma. She received five sessions of plasma exchange and her neurological symptoms gradually improved after surgery. This case highlights a rare case of GAD antibody-positive paraneoplastic SPS associated with mediastinal liposarcoma.