Endocrine Abstracts

Context: Subacute thyroiditis (SAT) is an inflammation of the thyroid, likely caused by a viral infection. IgG Autoantibodies (Ab) to the main thyroid antigens, including thyroglobulin (Tg) (TgAb) have been reported in a few patients with SAT and their appearance is usually transient. We investigated whether IgM TgAb can be detected in sera of patients with SAT.

Design: Serum samples were collected from 17 patients with SAT, ten with Graves’ disease (GD) and 10 with Hashimoto’s thyroiditis (HT). GD and HT sera were selected because of positive IgG TgAb (by AIA-PACK 2000, Tosoh Biosciences). Samples of SAT patients were collected 1–9 months after the onset of SAT. IgG and IgM TgAb were measured in ELISA. Wells coated with human Tg were incubated with sera and IgG and IgM TgAb were detected with biotin-conjugated anti human IgG or IgM. HRPO- conjugated streptadivin was then added. The substrate was o-phenylene diamine +H2O2. ODs were read at 490 nm. To rule out non-specific binding, ELISA for IgM was performed with BSA, keyhole limpet hemocyanin (KLH) and glucagon (Gluc); sera showing BSA binding were considered as IgM TgAb negative.

Results: IgG TgAb were positive in 14/17 SAT, 10/10 GD and 10/10 HT. IgM TgAb were positive in 10/17 SAT, 0/10 GD and 0/10 HT. Seven SAT sera were IgG TgAb positive and IgM TgAb negative, 5 IgG TgAb negative and IgM TgAb positive and 5 IgG TgAb positive and IgM TgAb positive. Median titer was 1/100 (IQR: 1/33-1/1000) for IgG TgAb and 1/3300 (IQR: 1/3300-1/3300) for IgM TgAb. The duration of SAT did not correlate with positive IgM TgAb. All SAT sera did not bind KLH and Gluc in IgM ELISA.

Conclusions: IgM TgAb can be detected in sera of SAT patients with or without IgG TgAb. They do not correlate with the duration of SAT.