de Quervain thyroiditis

**Etiology/Pathophysiology:** Believed to be post-viral (coxsackievirus, mumps, adenovirus, echovirus, influenza). Associated with HLA-B35. Viral-triggered inflammation damages follicles, causing release of preformed thyroid hormone (thyroglobulin, T3/T4) without new synthesis. Most common in women aged 30–50.

**Histology:** Granulomatous inflammation with multinucleated giant cells, neutrophil/lymphocyte infiltrates, and follicular disruption; later fibrosis and then regeneration.

**Clinical features:** - Preceding viral URI prodrome - Painful, tender, firm, diffusely or asymmetrically enlarged thyroid; pain often radiates to the jaw or ear - Fever, malaise, myalgias - Phases: (1) Thyrotoxic phase (weeks 2–8): palpitations, heat intolerance, tremor; (2) Hypothyroid phase (weeks to months): transient; (3) Recovery/euthyroid: most patients (about 90%) return to normal

**Labs/Diagnosis:** - Markedly elevated ESR and CRP - Early: high free T4/T3, suppressed TSH; the T4:T3 ratio is high because the release reflects stored hormone - Low (near zero) radioactive iodine uptake (RAIU) in the thyrotoxic phase, because the inflamed gland is not actively taking up or synthesizing hormone and TSH is suppressed - Thyroid autoantibodies (anti-TPO) are usually negative or low titer - Mild leukocytosis and mild anemia are possible

**Treatment:** Supportive and self-limited. - NSAIDs (aspirin or ibuprofen) for pain - Glucocorticoids (prednisone) for severe pain or inadequate NSAID response - Beta-blockers (propranolol) for adrenergic symptoms in the thyrotoxic phase - Antithyroid drugs (methimazole, PTU) are NOT indicated, since hormone synthesis is not increased - Levothyroxine may be needed temporarily if symptomatic hypothyroidism develops

**High-yield differentiators:** - Graves disease: painless, diffuse goiter, ophthalmopathy, pretibial myxedema, TSH receptor antibodies, HIGH diffuse RAIU - Hashimoto thyroiditis: painless goiter, anti-TPO/antithyroglobulin antibodies, Hürthle cells, lymphocytic infiltrate with germinal centers, hypothyroidism (risk of MALT/B-cell lymphoma) - Painless (silent/lymphocytic) thyroiditis and postpartum thyroiditis: painless, anti-TPO often positive, low RAIU, normal or mildly elevated ESR - Riedel thyroiditis: rock-hard, fixed, painless "woody" fibrosis extending beyond the thyroid, associated with IgG4-related disease, causes compressive symptoms - Acute suppurative thyroiditis: bacterial, fever, painful, normal thyroid function, often a pyriform sinus fistula (usually left-sided) in children - Exogenous thyroid hormone (thyrotoxicosis factitia): low RAIU, low thyroglobulin

**Exam pearl:** Painful thyroid + elevated ESR + low RAIU + recent viral illness = subacute granulomatous (de Quervain) thyroiditis. Treat with NSAIDs, not antithyroid drugs. Note that de Quervain tenosynovitis (inflammation of the abductor pollicis longus and extensor pollicis brevis tendons at the wrist) is a different condition named for the same Swiss surgeon, Fritz de Quervain.