Metastatic Chondroblastoma with Elevated Creatine Kinase and Paraneoplastic Neurologic Autoimmunity

A 17-year-old girl presented with chondroblastoma of the fibula and pulmonary metastases. Serum creatine kinase (CK) was elevated for a decade preoperatively and fell to near normal after tumor excision. An episode of aseptic meningitis 3 months later led to serologic detection of three antibody markers of paraneoplastic neurologic autoimmunity that in adult patients are characteristic of thymoma and lung carcinoma: muscle-type acetylcholine receptor (AChR) autoantibody (Ab), type 2 Purkinje cell cytoplasmic Ab (PCA-2), and collapsin response-mediator protein-5-IgG (CRMP-5-IgG). Locally recurrent chondroblastoma was excised 1 year later. Serum CK was elevated, CRMP-5-IgG was positive, PCA-2 was lower, and AChR Ab was undetectable. Three years after diagnosis she has stable pulmonary metastases, with elevated CK, higher PCA-2, positive CRMP-5-IgG, and undetectable AChR Ab. The association of metastatic chondroblastoma, elevated CK, and an evolving profile of paraneoplastic autoantibodies reveals a previously unrecognized immunobiologic dimension of chondroblastoma.