Hashimoto's thyroiditis and polyarthritis: a possible subset of seronegative polyarthritis.

Fifteen patients presenting with inflammatory polyarthritis who had Hashimoto's thyroiditis were investigated. Only 2/15 had frank myxoedema, 8/15 had incipient hypothyroidism (raised levels of thyrotropin or early symptoms of mild hypothyroidism), and 5/15 were euthyroid (thyrotropin levels normal). The presence or absence of rheumatoid factor (RF) distinguished two subgroups with different severity of synovitis. Nine out of 15 (group A) who remained RF negative throughout their follow-up had mild polyarthritis, lacked nodules or erosions on x-ray, and required, in addition to thyroid replacement, non-steroidal anti-inflammatory drugs for control of synovitis. Six out of 15 who remained RF positive (group B) had more severe synovitis, nodules, and erosive x-ray changes, and some required remittive drug treatment to control their disease. HLA-DR2 was present in 67% of group A and 13% of group B patients, while HLA-DR4 was present in 67% of group B and 33% of group A. Group A patients may represent a subset of patients with Hashimoto's thyroiditis and seronegative inflammatory polyarthritis, while group B patients appear to have features suggesting the coexistence of both rheumatoid arthritis and Hashimoto's thyroiditis.