Thyroid Research Thyroid Research Archive Hypothyroidism

Hyperprolactinemia is rare and of minor clinical importance in patients with hypothyroidism

(March 2003)

The background of the study. Patients with hypothyroidism may have high serum prolactin concentrations (hyperprolactinemia), which can cause reproductive disorders. In this study, the frequency of hyperprolactinemia in a large group of patients with hypothyroidism and its impact on the patients’ reproductive function were assessed.

How the study was done. One thousand three patients (938 women, 65 men) with hypothyroidism were studied. Among them, 93 patients had high serum thyrotropin (TSH) and low serum thyroxine (T4) concentrations (overt hypothyroidism) and 910 patients had high serum TSH and normal serum T4 concentrations (subclinical hypothyroidism). Serum prolactin was measured once in all patients.

The results of the study. Hyperprolactinemia was found in 8 percent of the women and 8 percent of the men. The frequency was similar in the patients with overt hypothyroidism (10 percent) and those with subclinical hypothyroidism (8 percent). The mean serum prolactin concentration was 49 ng/ml in the women with hyperprolactinemia (normal, <20 ng/ml) and 33 ng/ml in the men with hyperprolactinemia (normal, <18 ng/ml). There was no correlation between serum prolactin and TSH concentrations.

Seventeen (36 percent) of the premenopausal women with hyperprolactinemia had infrequent or no menstrual periods, as compared with 68 (16 percent) of the premenopausal women with normal serum prolactin concentrations. No woman who was not pregnant or nursing an infant was producing milk.

The conclusions of the study. Hyperprolactinemia is rare in patients with hypothyroidism, and most premenopausal women with hypothyroidism and hyperprolactinemia have normal menstrual cycles.

The original article. Raber W, Gessl A, Nowotny P, Vierhapper H. Hyperprolactinaemia in hypothyroidism: clinical significance and impact of TSH normalization. Clin Endocrinol 2003;58:185-91.