Postpartum thyroid disease: A model of immunologic dysfunction

Women with underlying, often asymptomatic, thyroid autoimmunity are at risk of developing postpartum thyroid disease/dysfunction (PPTD). While a few cases were reported in the 1800s, the frequent occurrence of PPTD was not described until 1948. Careful delineation of its multiple clinical presentations has emerged only in the past two decades. The sequential increase in cellular immune response at 1-4 months after delivery, followed by a humoral response at 7-10 months, is believed to underlie PPTD in susceptible women. The prevalence of thyroid autoimmunity, determined by positive thyroid peroxidase (TPO) or microsomal antibody titer postpartum, is 10% (range 2.8-26.4%; n = 18). The thyroid antibody test has a sensitivity of 0.71 (0.45-0.89), specificity 0.94 (0.90-0.98) and positive predictive value of 0.57 (0.40-0.78). A small percentage of women have detectable thyroid stimulating or inhibitory antibodies. Clinical expression is variable. Most common is a painless thyroiditis, with a hyperthyroid phase (due to release of stored thyroxine from damaged thyroid follicles) followed by a hypothyroid phase (during repair of the thyroid). This biphasic response is observed in 25% of patients, while the hyperthyroid phase only occurs in 24% and the hypothyroid phase alone in 40%. Sustained hyperthyroidism (Graves' disease) is present in 11% of these women. Management depends on severity and duration of symptoms. Hyperthyroidism due to thyroiditis is often mild and requires no therapy, although a β-blocker may help if adrenergic symptoms are prominent. Hyperthyroidism from Graves' disease requires definitive therapy. Hypothyroidism responds promptly to L-thyroxine (L-T₄). While most women recover and can discontinue L-T₄ after 6 to 12 months, long-term follow-up indicates that almost 20% of women remain permanently hypothyroid after an episode of PPTD. Optimal detection strategies are not yet defined. Education of health care providers and patients should lead to earlier detection. Laboratory testing of women at increased risk is also recommended.