To the Editor.
—The article on atypical hyperthyroidism by Joel I. Hamburger, MD, in the January Archives (139:96-98, 1979) did not refer to another condition that may cause thyrotoxicosis. Involvement of the thyroid by metastatic neoplasm is relatively common in patients with cancer, but seldom causes thyroid dysfunction.1 Hypothyroidism may develop after complete replacement of the thyroid by a tumor.1 Although rare, thyrotoxicosis could also result from destruction of the thyroid by a rapidly growing metastatic tumor; we have reported such occurrence in a patient with a nodular, poorly differentiated lymphocytic lymphoma.2 Since then, two additional cases appeared in the literature; one case was a pancreatic adenocarcinoma3 and the other, a breast carcinoma.4 However, such a phenomenon has not been observed in a primary thyroid cancer. Nontender, firm, and diffuse enlargement of the thyroid is found in association with a very low radioactive iodine uptake,