Laboratory Studies
Acute thyroiditis
Laboratory abnormalities in acute thyroiditis reflect the acute systemic illness. Findings include leukocytosis with a left shift and an increased sedimentation rate. Thyroid function test results are within the reference range.
Subacute thyroiditis
The primary laboratory abnormalities are consistent with abnormal thyroid function. Initially, the thyroid-stimulating hormone (TSH) level is suppressed, and the free thyroxine (T4) level is increased. As the disorder progresses, transient or sometimes permanent hypothyroidism may develop.
The WBC count is usually within the reference range but may be mildly elevated. High-sensitivity C-reactive protein levels are usually elevated in subacute thyroiditis.
Chronic thyroiditis
Laboratory abnormalities reflect thyroid function abnormality and evidence of autoimmunity.
TSH levels are increased in children with subclinical and overt hypothyroidism. Free T4 levels are within the reference range in the former and low in the latter. In children with hyperthyroidism, TSH levels are suppressed. Many children have normal thyroid function and normal TSH levels.
Antithyroid peroxidase (antithyrocellular, antimicrosomal) antibody levels elevated above the reference range are the most sensitive indicator of thyroid autoimmunity. Many children also have antithyroglobulin antibodies, although this is less sensitive and less specific.
Imaging Studies
Radioactive iodine thyroid scanning
Radioactive iodine thyroid scanning is not necessary for acute suppurative thyroiditis because the results are normal and do not aid in diagnosis. A scan may be helpful after diagnosis to identify a persistent thyroglossal duct as a route for infection.
This test is also unnecessary for chronic thyroiditis because the results can be misleading and may show increased uptake consistent with Graves disease, a multinodular goiter, or a hypofunctioning or hyperfunctioning nodule.
Radioactive iodine thyroid scanning is helpful in patients with hyperthyroidism who are thought to have subacute thyroiditis, because the extremely low uptake is consistent with the thyrocellular destruction in progress.
Thyroid ultrasonography
Thyroid ultrasonography is useful in revealing abscess formation in patients with acute thyroiditis.
The degree of hypoechogenicity on ultrasonography is related to the degree of thyroid dysfunction but its clinical use in chronic thyroiditis is questionable and does not alter management in children with chronic thyroiditis. [19]
A study by Lee and Kim on the ultrasonographic characteristics and interval changes of subacute thyroiditis found a high prevalence of nodular subacute lesions, as well variable interval changes. Out of 64 patients with subacute thyroiditis, 39 had nodular lesions, with 10 patients having both nodular and nonnodular lesions. Common interval changes were classified as “disappeared,” “decreased,” and “eventually smaller.” [20]
The overall of specificity of thyroid ultrasonography to identify specific concerns is questionable. A study in Germany found thyroid ultrasonography abnormalities in 40% of a random adult population, including nodules in 35.6%. [21]
A study by Nishihara et al reported that under ultrasonographic evaluation, hypoechoic inflammatory regions in subacute thyroiditis can severely obscure coexisting papillary carcinoma. Consequently, the investigators advised that ultrasonographic reexamination be performed after a sufficient interval in patients with subacute thyroiditis. [22]
Procedures
Fine-needle thyroid aspiration
This procedure is advocated by some to document the presence of thyroid lymphocytic infiltration in autoimmune thyroiditis. Histologic results are predictive of thyroid function; however, the results can be misinterpreted and can lead to unnecessary thyroid surgery.
Reserve this test for patients in whom underlying malignancy is suggested by a discrete thyroid nodule.
In patients with acute thyroiditis, needle aspiration can be used to obtain material for culture, enabling appropriate antibiotic therapy.
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Three multinuclear, giant cell granulomas observed in a fine-needle aspiration biopsy of the thyroid; from a patient with thyrotoxicosis from lymphocytic or subacute granulomatous thyroiditis.
