A 10-year-old girl presents with increasing fatigue, weight gain, cold intolerance, constipation, dry skin, and a diffusely enlarged, non-tender, firm goiter with a 'pebbly' surface. TSH is 18 mIU/L, free T4 is 0.6 ng/dL. Which antibody is most likely elevated and confirms the diagnosis?

• A Anti-thyroid-stimulating immunoglobulins (TSI)
• B Anti-thyroglobulin (anti-Tg) and anti-thyroid peroxidase (anti-TPO) antibodies ✓
• C Anti-TSH receptor blocking antibodies
• D Anti-microsomal antibodies only (anti-TPO absent)

Explanation

Hashimoto's thyroiditis (autoimmune lymphocytic thyroiditis) is the most common cause of acquired hypothyroidism in children. It is characterized by anti-TPO antibodies (most sensitive, present in >95%) and anti-thyroglobulin antibodies (less sensitive). The 'pebbly' or bosselated texture of the goiter reflects lymphocytic infiltration and fibrosis. TSI (thyroid-stimulating immunoglobulins) are the pathogenic antibody in Graves' disease (hyperthyroidism). Anti-TSH receptor blocking antibodies can cause atrophic autoimmune hypothyroidism without goiter.

Reference: Ghai Essential Pediatrics, 10th ed.

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Written and medically reviewed by the StethoPrep medical team.