Serum thyroid hormone antibodies are frequent in patients with polyglandular autoimmune syndrome type 3, particularly in those who require thyroxine treatment
Polyglandular autoimmune syndrome (PAS) type 3 consists of autoimmune thyroid
disease (AITD) coexisting with ≥1 non-thyroidal autoimmune disease (NTAID) other
than Addison’s disease and hypoparathyroidism. We evaluated the prevalence and
repertoire of thyroid hormones antibodies (THAb) in PAS-3 patients. Using a radioimmunoprecipation technique, we measured THAb (T3IgM, T3IgG, T4IgM, and T4IgG) in
107 PAS-3 patients and 88 controls (patients with AITD without any NTAID). Based
on the selective coexistence of AITD with one NTAID (chronic autoimmune gastritis,
non-segmental vitiligo or celiac disease), patients were divided into group 1 (chronic
autoimmune gastritis positive, n = 64), group 2 (non-segmental vitiligo positive, n = 24),
and group 3 (celiac disease positive, n = 15). At least one of the four THAb was detected
in 45 PAS-3 patients (42.1%) and 28 controls (31.8%, P = 0.14), with similar rates
in the three PAS-3 groups. The rates of T3Ab, T4Ab, and T3 + T4Ab were similar in
groups 1 and 2, while in group 3, T3Ab was undetected (P = 0.02). In PAS-3 patients,
the rate of levothyroxine treatment was greater in THAb-positive patients compared to
THAb-negative patients (76.7 vs. 56.1%, P = 0.03, RR = 1.4, 95% CI 1.03–1.81). Not
unexpectedly, levothyroxine daily dose was significantly higher in group 1 and group 3,
namely in patients with gastrointestinal disorders, compared to group 2 (1.9 ± 0.4 and
1.8 ± 0.3 vs. 1.5 ± 0.2 μg/kg body weight, P = 0.0005 and P = 0.004). Almost half of
PAS-3 patients have THAb, whose repertoire is similar if chronic autoimmune gastritis
or celiac disease is present. A prospective study would confirm whether THAb positivity
predicts greater likelihood of requiring levothyroxine treatment
