Consumptive hypothyroidism caused by paraneoplastic production of type 3 iodothyronine deiodinase.

Consumptive hypothyroidism is characterized by excessive inactivation of thyroid hormone by type 3 iodothyronine deiodinase (D3). Previously this rare syndrome was described in association with massive hemangiomas in children and in a single case of a hemangioendothelioma in an adult. Here we report the first case of consumptive hypothyroidism from a nonvascular tumor in a patient who required supraphysiologic doses of levothyroxine prior to the resection of a large malignant solitary fibrous tumor. The tumor expressed D3 message, protein and exhibited functional D3 enzymatic activity. The clinical presentation of this patient expands the differential diagnosis of hypothyroidism, adds to the growing list of paraneoplastic syndromes that impact the endocrine system, and extends the spectrum of tumor types associated with consumptive hypothyroidism.