What are the diagnostic criteria for Hashimoto's (Hashimoto's thyroiditis)?

Diagnostic Criteria for Hashimoto's Thyroiditis

The diagnosis of Hashimoto's thyroiditis is primarily based on the demonstration of circulating antibodies to thyroid antigens (mainly thyroperoxidase and thyroglobulin) and reduced echogenicity on thyroid sonogram in a patient with appropriate clinical features. 1

Clinical and Laboratory Criteria

• Thyroid Antibodies: Elevated thyroid peroxidase antibodies (TPOAb) and thyroglobulin antibodies (TgAb) are the hallmark laboratory findings 2, 1
• Thyroid Function Tests: TSH and free T4 should be measured to determine thyroid function status 3
  • Patients may present with euthyroid, hypothyroid, or occasionally hyperthyroid states 1
  • Elevated TSH with normal or low free T4 indicates subclinical or overt hypothyroidism, respectively 3
• Ultrasound Findings: Reduced echogenicity on thyroid sonogram is characteristic 1
  • Heterogeneous echotexture and increased thyroid vascularity are supportive findings 2
  • Note that imaging is not required for diagnosis of hypothyroidism in adults when laboratory tests are definitive 3

Clinical Presentation

• Symptoms: May include fatigue, weight gain, cold intolerance, constipation, hair loss, and voice changes 3
• Physical Examination: Often reveals a painless goiter, although the thyroid may be normal in size or atrophic in later stages 4, 1
• Disease Course: Most forms of Hashimoto's thyroiditis eventually progress to hypothyroidism, although patients may initially be euthyroid or even hyperthyroid 1

Comprehensive Scoring System

A multi-criteria scoring system has been proposed that combines:

• TPOAb levels
• TgAb levels
• Thyroid vascularity on ultrasound

This scoring system has demonstrated better performance than any single predictor in identifying patients with Hashimoto's thyroiditis and those at higher risk of developing hypothyroidism 2

Associated Conditions

• Hashimoto's thyroiditis is frequently associated with other autoimmune diseases 3, 5:
  • Autoimmune thyroid disease (AITD) is the most common autoimmune comorbidity 3
  • Other associated conditions include alopecia, vitiligo, celiac disease, and type 1 diabetes 5

Clinical Variants

Several clinicopathologic entities are included under the term Hashimoto's thyroiditis 1:

• Classic form (lymphocytic goiter)
• Fibrous variant
• IgG4-related variant
• Juvenile form
• Hashitoxicosis
• Painless thyroiditis (sporadic or post-partum)

Diagnostic Pitfalls and Caveats

• Normal IgG levels do not preclude the diagnosis of Hashimoto's thyroiditis 3
• Obese children may have an ultrasound pattern similar to Hashimoto's thyroiditis without actually having the disease 5
• There is no role for imaging studies (CT, MRI, FDG-PET/CT, or radionuclide scans) in the routine workup of hypothyroidism in adults 3
• Cytologic examination from fine-needle aspiration may occasionally be required to differentiate Hashimoto's thyroiditis from other thyroid disorders, particularly when nodules are present 3

In conclusion, the diagnosis of Hashimoto's thyroiditis relies on a combination of clinical features, thyroid antibody testing, and ultrasound findings. While imaging studies beyond ultrasound are not routinely indicated, they may be necessary in cases with atypical presentations or when other thyroid disorders need to be excluded.