Chronic lymphocytic thyroiditis (CLT), an autoimmune condition, is the most common cause of goiter in the pediatric population. Its incidence is highest in adolescent girls, with a female-to-male ratio of 2:1.

Some patients with CLT present for medical examination with symptoms of hypothyroidism (Table 36-1). Most have enlargement of the gland without systemic complaints. Rarely, patients with CLT present with symptoms of hyperthyroidism (Hashitoxicosis). These children usually progress toward hypothyroidism over a period of months. The thyroid gland itself is diffusely enlarged (although possibly with asymmetry), mobile, nontender, firm, or rubbery. It usually has a granular or pebbly texture but can be smooth. However, in the most severe cases of hypothyroidism and CLT, the thyroid is often so degenerated that it is not easily palpable. Enlargement of the thyroid in CLT may be caused by lymphocytic infiltration or stimulation by the increased TSH. A goiter due to increased TSH stimulation typically decreases with treatment.

There is a family history of thyroid disease in 30% to 40% of patients with CLT. Histologic findings include infiltration of the gland with plasma cells and lymphocytes, parenchymal atrophy, and eosinophilic degeneration of thyroid follicles.

Laboratory studies should include assessment of T₄ and/or free T₄, TSH, and antithyroglobulin and antithyroperoxidase antibodies. In children with CLT, thyroid function tests indicate either a euthyroid state (no abnormalities), compensated hypothyroidism (normal level of T₄ with increased TSH), or hypothyroidism (low level of T₄ with increased TSH). One or both of the antithyroid antibodies are present in 90% to 95% of patients with CLT. These antibodies represent the immunologic response to the presence of elements of thyroid tissue in the bloodstream and are not the cause of the thyroiditis. In general, routine ultrasound (US) imaging of the thyroid is unnecessary. However, patients with Hashimoto disease are at an increased risk of developing thyroid nodules. If the patient presents with an asymmetric gland, or an easily palpated nodule, US imaging should be pursued. US imaging will typically reveal thyroid gland enlargement with heterogeneous echotexture. “Pseudonodules” are commonly found, and are distinguished from true nodules by confirming their presence in more than one imaging plane (sagittal and transverse). If a nodule is found, fine needle aspiration biopsy should be performed (see below).

Sporadic nontoxic goiter is the second most common cause of nontoxic thyroid enlargement in the pediatric population. Its cause is uncertain, although an autoimmune cause is a possibility. There is often a family history of goiter and/or hypothyroidism.

There is diffuse enlargement of the thyroid gland in asymptomatic adolescents. The gland is enlarged and usually softer and more homogeneous than in CLT. Nodularity may develop after several years, even in those patients in whom regression has occurred.

There are usually no antithyroid antibodies, and the T₄ and TSH levels are normal. Patients should be followed with repeat physical examination and serial thyroid function testing (TSH and T₄) every 6 to 12 months to ensure that thyroid gland dysfunction does not develop. Ultrasound is not indicated unless there is a suspicion of a thyroid nodule.

Graves disease, a multisystem autoimmune disorder, is the most common cause of hyperthyroidism in the pediatric population. The incidence in males and females is equal in infancy and early childhood, with a female predominance occurring in adolescence. In Graves disease, elaboration of an immunoglobulin G1 antibody stimulates the TSH receptor, resulting in hyperfunctioning follicular cells with increased production and release of thyroid hormone. The predominant antibody acts to stimulate the TSH receptor causing both hyperthyroidism and a goiter. Mild exophthalmos is common in pediatric patients with Graves disease; however, it is usually less severe than what is seen in adults with exophthalmos.