(See also Overview of Thyroid Function.)
The term "silent" refers to the absence of thyroid tenderness in contrast with subacute thyroiditis, which usually causes thyroid tenderness.
Silent lymphocytic thyroiditis causes most cases of postpartum thyroid dysfunction. It occurs in about 5 to 10% of postpartum women.
Thyroid biopsy reveals lymphocytic infiltration as in Hashimoto thyroiditis but without lymphoid follicles and scarring. Thyroid peroxidase autoantibodies and, less commonly, antithyroglobulin antibodies are almost always positive during pregnancy and the postpartum period in these patients. Thus, this disorder would appear to be a variant of Hashimoto thyroiditis.
The condition begins in the postpartum period, usually within 12 to 16 weeks. Silent lymphocytic thyroiditis is characterized by a variable degree of painless thyroid enlargement with a hyperthyroid phase of several weeks, often followed by transient hypothyroidism due to depleted thyroid hormone stores but usually eventual recovery to the euthyroid state (as noted for painful subacute thyroiditis). The hyperthyroid phase is self-limited and may be brief or overlooked. Many women with this disorder are diagnosed when they become hypothyroid, which occasionally is permanent.
Silent lymphocytic thyroiditis is frequently undiagnosed. Suspicion of the diagnosis generally depends on clinical findings, typically once hypothyroidism has occurred. Eye signs and pretibial myxedema do not occur.
Thyroid function test results vary depending on the phase of illness. Initially, serum T4 and T3 are elevated and TSH is suppressed. In the hypothyroid phase, these findings are reversed. White blood cell count and erythrocyte sedimentation rate are normal. Needle biopsy provides definitive diagnosis but is usually unnecessary.
Because silent lymphocytic thyroiditis lasts only a few months, treatment is conservative, usually requiring only a beta-blocker (eg, propranolol) during the hyperthyroid phase. Antithyroid drugs, surgery, and radioiodine therapy are contraindicated.
Thyroid hormone replacement may be required during the hypothyroid phase. Most patients recover normal thyroid function, although some remain permanently hypothyroid. Therefore, thyroid function should be reevaluated after 9 to 12 months of thyroxine therapy; replacement is stopped for 5 weeks, and TSH is remeasured. This disorder usually recurs after subsequent pregnancies.
Silent lymphocytic thyroiditis affects mostly women in the postpartum period.
Most patients go through a transient hyperthyroid phase, followed by a longer hypothyroid phase; most, but not all, recover spontaneously.
The disorder often goes undiagnosed.
A beta-blocker is often needed in the hyperthyroid phase, and thyroid hormone replacement is typically needed in the hypothyroid phase.