A CASE OF GRAVES-DISEASE WITH FALSE HYPERTHYROTROPINEMIA WHO DEVELOPED SILENT THYROIDITIS

We encountered a patient who developed silent thyroiditis during the c ourse of Graves' disease. The diagnosis of silent thyroiditis was made on the basis of a low thyroidal I-131 uptake, no response to the thyr otropin releasing hormone (TRH) test, and subsequent hypothyroidism de spite the presence of high titers of thyrotropin (TSH) receptor antibo dy (TRAb) and thyroid stimulating antibody (TSAb). The patient, in add ition, had a discrepancy between serum TSH and thyroid hormone values. This was due to the presence of interfering substances that react to mouse IgG in the sera since serum TSH levels were decreased in a dose dependent manner by the addition of increasing amounts of mouse IgG to the sera. It should therefore be noted that silent thyroiditis can de velop in patients with Graves' disease. Furthermore, clinicians should be aware that two-site immunoassay kits that use mouse monoclonal ant ibodies are subject to interference by some substances, possibly antib odies which react to mouse IgG.