A variant of thyrotoxicosis associated with chronic thyroiditis characterized by prolonged fever, absence of anti-thyroidal antibodies, and favorable response to naproxen.

An unusual form of thyrotoxicosis due to chronic thyroiditis is described. A 78-year-old debilitated woman was admitted because of fever to 38 degrees C persisting for the previous 16 months, for which the antipyretic effect of diclofenac sodium and pranoprofen had been insufficient or transient. Intense accumulation of gallium-67 citrate in the thyroid gland provided an initial clue to the diagnosis of masked thyrotoxicosis as a cause of the fever, and naproxen (300 mg/d) eliminated the fever and flaring of thyrotoxicosis. Despite the absence of autoantibodies related to chronic thyroiditis, needle biopsy revealed destructive thyroiditis due to chronic lymphocytic thyroiditis. This case suggests a previously unrecognized variant of thyrotoxicosis due to chronic thyroiditis, that is, neither painless thyroiditis nor acute exacerbation of Hashimoto thyroiditis, and instead characterized by prolonged fever, nontender thyroid, absence of antibodies associated with autoimmune thyroiditis, and excellent response to naproxen.