The prevalence of polycystic thyroid disease in hypothyroid patients with negative thyroid autoantibodies

We previously reported that multiple thyroid cysts may be a cause of hypothyroidism in patients with a relatively high iodine intake and we termed it polycystic thyroid disease (PCTD). The aim of this study was to investigate the prevalence of PCTD in patients who visited our thyroid center. We hypothesized that patients with PCTD are not rare in a region with a high iodine intake.

We retrospectively studied the cause of hypothyroidism based on medical histories and ultrasonography in new patients to our hospital from April 2008 to March 2009 whose serum tests for antithyroglobulin antibodies (TgAb) and thyroid peroxidase antibodies (TPOAb) were negative. Serum thyroid hormones, thyrotropin (TSH), TgAb, and TPOAb were measured in 8243 patients. Patients with four or more thyroid cysts, negative tests for TgAb and TPOAb, no evidence for thyroid diseases other than their thyroid cysts, and no exposure to thyroid-perturbing influences were defined as having PCTD.

Three hundred seven patients had overt hypothyroidism (TSH level above 10.0 μU/mL and free thyroxine level below 0.7 ng/dL), of whom 71 patients were both TgAb and TPOAb negative. There were 546 patients with subclinical hypothyroidism (TSH level above 5.0 μU/mL and normal free thyroxine), of whom 193 patients were both TgAb and TPOAb negative. There were 24 patients with overt hypothyroidism and PCTD, accounting for 7.8% (24/307) of all causes of overt hypothyroidism. There were 42 patients with subclinical hypothyroidism and PCTD, accounting for 7.7% (42/543) of all causes of subclinical hypothyroidism. PCTD was more common among elderly people than young people.

PCTD appears to be a minor but not negligible cause of hypothyroidism, at least in iodine-rich regions. PCTD with hypothyroidism may have been misdiagnosed as thyroid antibody-negative Hashimoto's thyroiditis in many reports.