Transient Elevation of Triiodothyronine Caused by Triiodothyronine Autoantibody Associated with Acute Epstein-Barr-Virus Infection

Abstract

A unique 16-year old female patient presented after acute Epstein-Barr virus (EBV) infection with severe primary hypothyroidism. Her thyroid test results were thyrotropin level (TSH) of 198 mU/L (normal, 0.4-4 mU/L), free thyroxine [FT₄], 2.5 pmol/L (normal, 10-25 pmol/L), total triiodothyronine (TT₃) > 19.5 nmol/L (normal, 1.3-2.7 nmol/L), and free triiodothyronine (FT₃), 0.77 pmol/L (normal, 3.3-6.3 pmol/L). She had high titers of thyroglobulin and thyroid peroxidase autoantibodies. In vitro triiodothyronine (T₃)-binding measured by radioimmunoprecipitation was 86% (normal, up to 8.5%) and thyroxine (T₄)-binding 8.2% (normal, 6.4%). Serum immunoglobulin G (IgG) absorption, achieved by protein-G Sepharose beads, decreased TT₃ toward normal. Levothyroxine treatment normalized the low baseline FT₄ and FT₃ values, and suppressed TSH to normal. However, TT₃ remained highly elevated and returned to normal after 20 months, while T₃ binding gradually decreased. Thus, her severe hypothyroidism was masked by this unusual phenomenon. Thirty-four patients with EBV infection (15 with acute disease and 19 with previous infection) were tested for thyroid hormone levels. EBV antibodies (early antigen immunoglobulin M [IgM] and IgG and anti-Epstein-Barr virus nuclear antigen [EBNA] IgG) were measured by enzyme-linked immunosorbent assay (ELISA). In 15 patients with acute EBV the mean TT₃ level was 2.47 ± 0.39 nmol/L (5 had TT₃ values above normal) compared to a mean TT₃ of 1.70± 0.53 nmol/L in 19 subjects with previous infection (p < 0.0005; only 1 had a TT₃ result above normal), with no differences in FT₄ and TSH concentrations between the two groups. Acute EBV infection may be associated with transient mild to severe TT₃ elevation as a result of assay interference by anti-T₃ autoantibodies.