Thyroiditis: Clinical Features and Management

Classification Overview

• Harrison's Principles of Internal Medicine 22E, p. 3081 (Table 396-3)

1. Acute (Suppurative) Thyroiditis

Clinical Features

• Rare; caused by bacterial infection (Staphylococcus, Streptococcus, Enterobacter) or fungal organisms in immunocompromised patients
• In children/young adults: often due to a piriform sinus (4th branchial pouch remnant, predominantly left-sided)
• Thyroid pain, often referred to the throat or ears
• Small, tender, asymmetric goiter; fever, dysphagia, erythema over thyroid, lymphadenopathy
• ESR and WBC elevated; thyroid function usually normal
• FNA shows PMN infiltration; culture identifies organism

Management

• Antibiotics guided by Gram stain and FNA cultures
• Surgery to drain abscess (localized by CT/ultrasound) if needed
• Complications if untreated: tracheal obstruction, septicemia, mediastinitis, jugular venous thrombosis
• Harrison's, p. 3081

2. Subacute Granulomatous Thyroiditis (De Quervain's)

Epidemiology

• Most common cause of a painful thyroid gland
• Accounts for ~5% of clinical thyroid disorders
• Peak incidence 30-50 years; women affected 3-5x more than men
• Often follows viral prodrome (mumps, coxsackie, influenza, adenovirus, echovirus, SARS-CoV-2)

Pathophysiology

Clinical Features

• Painful, enlarged thyroid (often exquisitely tender), sometimes asymmetric
• Pain referred to jaw or ear
• Malaise, low-grade fever, sore throat (may mimic pharyngitis)
• Symptoms of thyrotoxicosis or hypothyroidism depending on phase
• In 10%: acute, severe onset with marked hyperthyroid symptoms
• In 33%: asymptomatic except for goiter

1. Thyrotoxic phase (weeks 1-6): raised T4/T3, suppressed TSH, low radioiodine uptake (<5%)
2. Hypothyroid phase (weeks 6-12): low T4, elevated TSH
3. Recovery phase (weeks 12-18+): normalization of all tests

Investigations

• ESR markedly elevated (often >50 mm/h)
• Low radioiodine uptake or 99mTc pertechnetate uptake (distinguishes from Graves' disease)
• T4:T3 ratio lower than in Graves' (stored hormone release rather than de novo synthesis)
• Thyroid antibodies negative
• FNA (if needed): giant cells, granulomas

Management

• Most patients recover fully within 6 months
• Permanent hypothyroidism in ~15% (especially if coincident thyroid autoimmunity)
• Recurrence uncommon but possible
• Harrison's, p. 3082; Goldman-Cecil Medicine, p. 2440; Bailey and Love's Surgery 28e, p. 893

3. Hashimoto's Thyroiditis (Chronic Autoimmune Thyroiditis)

Epidemiology

• Most common cause of hypothyroidism in iodine-sufficient regions
• Peak age 45-65 years; female predominance 10:1 to 20:1
• Strong genetic component: CTLA4, PTPN22, IL2RA polymorphisms

Pathogenesis

Histology

Clinical Features

• Painless goiter - diffuse, symmetric, firm, "bosselated" texture
• Gradual onset of hypothyroid symptoms: fatigue, weight gain, cold intolerance, constipation, impaired concentration, dry skin, hair loss
• Early phase: sometimes hashitoxicosis (transient thyrotoxicosis from follicular disruption)
• Eventually: primary myxoedema (end stage, no goiter)
• Associated autoimmune diseases: T1DM, Addison's disease, SLE, myasthenia gravis, Sjögren's syndrome
• Increased risk of thyroid lymphoma (most lymphomas arise on a background of lymphocytic thyroiditis)

Investigations

• TSH elevated; free T4 low (or normal in subclinical hypothyroidism)
• Anti-TPO antibodies positive in >90% (anti-thyroglobulin also elevated)
• Ultrasound: heterogeneous, hypoechoic gland
• FNA: oncocytes + heterogeneous lymphocytes (characteristic)

Management

• Levothyroxine replacement for overt hypothyroidism (titrate to normalize TSH)
• Subclinical hypothyroidism (elevated TSH, normal T4): treat if TSH >10 mIU/L, or if symptomatic, pregnant, or planning pregnancy
• Monitor thyroid function annually if not on replacement
• Goiter causing compressive symptoms: levothyroxine may reduce size; surgery rarely needed
• Robbins & Cotran, p. 998-999; Bailey and Love's, p. 893

4. Postpartum / Sporadic Silent (Painless) Thyroiditis

Epidemiology

• Postpartum thyroiditis: up to 10% of pregnancies; 20x more common postpartum than Graves' disease
• More frequent with positive anti-TPO antibodies in 1st trimester or personal/family history of autoimmunity
• Sporadic (non-postpartum) silent thyroiditis: age 30-60, female > male (1.5:1)
• Both are variants of the same autoimmune destruction-induced thyroiditis

Clinical Features

• Painless goiter (nontender)
• Classic sequence: thyrotoxic phase (1-3 months) → euthyroid (1-2 months) → hypothyroid phase (up to 12 months)
• Not all patients complete the full sequence: ~25% experience only thyrotoxicosis; ~50% only hypothyroidism
• Thyrotoxic phase: tachycardia, palpitations, heat intolerance (milder than Graves')
• Hypothyroid phase: fatigue, constipation, cold intolerance, impaired concentration

Diagnosis

• Toxic phase: raised free T4/T3, suppressed TSH; T3:T4 ratio <20 (distinguishes from Graves')
• Anti-TPO antibodies positive; TSH-receptor antibodies negative (key distinction from Graves')
• Low/absent radioiodine uptake; ultrasound: heterogeneous, hypoechoic; Doppler flow markedly decreased (vs. increased in Graves')

Management

• Self-limiting course
• Thyrotoxic phase: beta-blockers (atenolol 25-50 mg/day) for moderate/severe symptoms; antithyroid drugs NOT effective
• Hypothyroid phase: levothyroxine if symptomatic or severe; taper after 6-12 months to reassess recovery
• Pregnancy: continue levothyroxine throughout pregnancy if initiated
• Prognosis: up to 50% remain chronically hypothyroid; recurs after 70% of subsequent pregnancies; higher risk with high anti-TPO titers
• Goldman-Cecil Medicine, p. 2439-2440

5. Riedel's Thyroiditis

• Very rare (0.5% of goiters)
• Thyroid replaced by cellular fibrous tissue that infiltrates surrounding structures (trachea, muscles, parathyroids, recurrent laryngeal nerve)
• Presents as a rock-hard, fixed goiter with compressive symptoms (dysphagia, stridor, hypothyroidism)
• Associated with IgG4-related systemic disease and other fibrosclerotic conditions
• Management: surgery to relieve compression; corticosteroids; tamoxifen (antifibrotic); levothyroxine for hypothyroidism
• Bailey and Love's, p. 893

Drug-Induced Thyroiditis

Summary Table: Key Distinguishing Features