How do you diagnose Hashimoto's (thyroiditis)?

How to Diagnose Hashimoto's Thyroiditis

The diagnosis of Hashimoto's thyroiditis relies on demonstrating circulating antibodies to thyroid antigens (primarily anti-thyroid peroxidase [TPO] and anti-thyroglobulin [TgAb]) combined with reduced echogenicity on thyroid ultrasound in a patient with compatible clinical features. 1

Initial Laboratory Testing

• Measure TSH as the primary screening test when Hashimoto's thyroiditis is suspected, as it is the most sensitive marker for thyroid dysfunction with sensitivity above 98% and specificity greater than 92%. 2

• Obtain both TSH and free T4 (FT4) simultaneously to distinguish between different thyroid states: elevated TSH with low FT4 indicates overt hypothyroidism, elevated TSH with normal FT4 indicates subclinical hypothyroidism, and normal TSH with normal FT4 suggests euthyroid status. 2

• Confirm abnormal TSH findings with repeat testing after 3-6 weeks, as 30-60% of elevated TSH levels normalize spontaneously on repeat measurement, potentially representing transient thyroiditis. 3

Antibody Testing for Definitive Diagnosis

• Measure anti-thyroid peroxidase (TPO) antibodies as the primary autoimmune marker, as these are elevated in Hashimoto's thyroiditis and confirm the autoimmune etiology. 1, 4

• Measure anti-thyroglobulin (TgAb) antibodies in addition to TPO antibodies, particularly in patients with significant symptom burden, as elevated TgAb levels correlate with increased symptoms including fragile hair, face edema, eye edema, and harsh voice. 5

• Positive TPO antibodies identify patients at higher risk of progression to overt hypothyroidism (4.3% per year versus 2.6% per year in antibody-negative individuals), making this test critical for risk stratification. 3

Imaging Studies

• Perform thyroid ultrasound to assess for reduced echogenicity, which is characteristic of Hashimoto's thyroiditis and represents lymphocytic infiltration of the thyroid gland. 1, 4

• Use ultrasound to evaluate thyroid volume and identify any nodules that may require further evaluation, as surgery may be indicated when nodules cannot be confirmed as benign by cytology. 1

• Be cautious interpreting ultrasound findings in obese children, as they may have echographic patterns similar to Hashimoto's thyroiditis without actually having the disease. 6

Clinical Presentation to Assess

• Look for symptoms of hypothyroidism including fatigue, muscle cramps, constipation, cold intolerance, hair loss, voice changes, weight gain, intellectual slowness, and insomnia. 2

• Examine for painless goiter, which is commonly present in Hashimoto's thyroiditis, distinguishing it from subacute thyroiditis which presents with anterior neck pain. 1, 4

• Recognize that thyroid function at presentation is variable, ranging from euthyroid to hyperthyroid (Hashitoxicosis) to hypothyroid, with most patients ultimately evolving to hypothyroidism. 1, 6

Diagnostic Algorithm Based on Findings

For patients with elevated TSH and positive TPO antibodies:

• This confirms Hashimoto's thyroiditis with hypothyroidism requiring treatment consideration. 1, 4

For patients with normal TSH but positive TPO antibodies and reduced echogenicity on ultrasound:

• This represents euthyroid Hashimoto's thyroiditis requiring monitoring every 6-12 months for progression to hypothyroidism. 4, 7

For patients with elevated TSH >10 mIU/L:

• Initiate levothyroxine therapy regardless of symptoms, as this level carries approximately 5% annual risk of progression to overt hypothyroidism. 3

For patients with TSH 4.5-10 mIU/L:

• Consider treatment if symptomatic or if positive TPO antibodies are present, given the higher progression risk. 3

Common Pitfalls to Avoid

• Do not diagnose based on a single elevated TSH value, as transient elevations are common and may represent recovery phase from thyroiditis rather than Hashimoto's disease. 3

• Do not rely on T4 levels alone to exclude thyroid dysfunction, as subclinical hypothyroidism (elevated TSH with normal T4) represents a clinically significant condition that may require treatment. 3

• Do not overlook screening for associated autoimmune diseases including alopecia, vitiligo, celiac disease, and type 1 diabetes, which frequently coexist with Hashimoto's thyroiditis. 6

• Do not assume all patients with Hashimoto's thyroiditis are hypothyroid at presentation, as some may be euthyroid or even hyperthyroid initially before progressing to hypothyroidism. 1, 7

Special Populations

In pregnant or postpartum women:

• Hashimoto's disease is the most common cause of hypothyroidism in industrialized nations during pregnancy, and untreated maternal hypothyroidism increases risk of preeclampsia and low birth weight. 2

In children and adolescents:

• The most common initial presentation is subclinical hypothyroidism (39.5%), followed by euthyroidism (36.5%), with continuous monitoring required due to the dynamic nature of the disease. 7

• Treatment with levothyroxine should be started promptly in frank hypothyroidism, but for TSH between upper reference level and 10 µU/ml without symptoms, avoid treatment unless TSH remains constantly above 10 µU/ml. 6