What is the appropriate workup and management for a patient with suspected thyroiditis?

Workup of Thyroiditis

Initial Laboratory Assessment

Measure TSH, free T4, and thyroid peroxidase (TPO) antibodies as the essential first-line tests to establish the diagnosis and type of thyroiditis. 1, 2

• TSH and free T4 distinguish between the hyperthyroid, euthyroid, and hypothyroid phases of thyroiditis, with TSH suppressed during thyrotoxicosis and elevated during hypothyroidism 1, 2
• TPO antibodies identify autoimmune thyroiditis (Hashimoto's), which is the most common form and presents with elevated TPO antibodies in the setting of hypothyroidism or goiter 1, 2
• Erythrocyte sedimentation rate (ESR) is markedly elevated in subacute granulomatous thyroiditis (often >50 mm/hr) but normal in other forms, making it useful for distinguishing painful subacute thyroiditis from other causes 3
• Thyroglobulin level is elevated in destructive thyroiditis (subacute granulomatous and lymphocytic) due to release of preformed hormone, confirming thyroid inflammation 3

Clinical Presentation Guides Diagnosis

• Hashimoto thyroiditis presents with painless goiter, hypothyroidism symptoms (fatigue, weight gain, cold intolerance, constipation), and elevated TPO antibodies—this is the most common form encountered in primary care 1, 2
• Subacute granulomatous thyroiditis presents with anterior neck pain (often severe), fever, and symptoms of hyperthyroidism following an upper respiratory viral illness 2, 4
• Postpartum thyroiditis occurs within one year of delivery, miscarriage, or medical abortion, typically presenting with transient hyperthyroidism followed by hypothyroidism 1, 2
• Subacute lymphocytic thyroiditis (silent thyroiditis) is painless, presents with hyperthyroidism symptoms, and often occurs postpartum 5, 3
• Acute suppurative thyroiditis presents with fever, severe anterior neck pain, and signs of bacterial infection—this is rare but requires urgent antibiotic treatment 5, 3

Radioactive Iodine Uptake (RAIU) Scan—When to Order

Order RAIU scan only when the diagnosis is unclear or when distinguishing between Graves' disease and destructive thyroiditis is necessary. 6, 2

• Low or absent RAIU (<5% at 24 hours) confirms destructive thyroiditis (subacute granulomatous, lymphocytic, or postpartum) rather than Graves' disease, which shows elevated uptake 6, 2
• RAIU is not needed for Hashimoto thyroiditis diagnosis, as elevated TPO antibodies and clinical presentation are sufficient 6
• RAIU is not indicated for hypothyroidism workup, as all causes show decreased uptake 6

Thyroid Ultrasound—Limited Role

• Ultrasound can identify nodules if palpable abnormalities are present, but imaging is not routinely necessary for thyroiditis diagnosis 6
• Doppler ultrasound may show increased blood flow in Graves' disease versus decreased flow in destructive thyroiditis, but RAIU remains the preferred test 6
• Ultrasound has no role in diagnosing or managing hypothyroidism from Hashimoto thyroiditis 6

Triphasic Disease Pattern Recognition

Most forms of thyroiditis follow a predictable triphasic pattern: initial hyperthyroidism, followed by hypothyroidism, then recovery to normal function. 1, 2

• Phase 1 (Thyrotoxicosis): Preformed thyroid hormone is released from damaged follicles, causing suppressed TSH, elevated free T4, and hyperthyroid symptoms (palpitations, tremor, heat intolerance, weight loss) 1, 2
• Phase 2 (Hypothyroidism): Thyroid hormone stores become depleted, causing elevated TSH, low free T4, and hypothyroid symptoms (fatigue, weight gain, cold intolerance, constipation) 1, 2
• Phase 3 (Recovery): Thyroid function normalizes in most patients, though 20-30% develop permanent hypothyroidism requiring lifelong levothyroxine 1, 2

Management Based on Thyroiditis Type

Hashimoto Thyroiditis

• Treat with levothyroxine for overt hypothyroidism (elevated TSH with low free T4) or symptomatic subclinical hypothyroidism (elevated TSH >10 mIU/L with normal free T4) 7, 1
• Start levothyroxine at 1.6 mcg/kg/day in patients <70 years without cardiac disease, or 25-50 mcg/day in elderly or cardiac patients 7
• Monitor TSH every 6-8 weeks during dose titration, then every 6-12 months once stable 7

Subacute Granulomatous Thyroiditis

• NSAIDs (ibuprofen 600 mg three times daily) or aspirin for mild to moderate thyroid pain 2, 4
• Prednisone 40 mg daily for severe pain unresponsive to NSAIDs, with rapid symptom relief expected within 24-48 hours 4
• Beta blockers (propranolol or atenolol) for hyperthyroid symptoms during the thyrotoxic phase 6, 2
• Levothyroxine is generally not needed during the hypothyroid phase unless TSH >10 mIU/L or severe symptoms develop 6, 2
• Recheck TSH and free T4 every 2-3 weeks to monitor transition between phases 6

Postpartum Thyroiditis

• Beta blockers for symptomatic hyperthyroidism in the initial phase 2
• Levothyroxine for hypothyroid phase if TSH >10 mIU/L, or TSH 4-10 mIU/L with symptoms or desire for fertility 2
• Monitor TSH every 4-6 weeks for the first year postpartum to detect phase transitions 2

Drug-Induced Thyroiditis (Immune Checkpoint Inhibitors)

• Continue immunotherapy in most cases, as thyroid dysfunction rarely requires treatment interruption 6
• Beta blockers for symptomatic thyrotoxicosis 6
• Monitor TSH every 2-3 weeks after diagnosis to catch transition to hypothyroidism 6
• Endocrine consultation for persistent thyrotoxicosis >6 weeks or severe symptoms (Grade 3-4) 6
• Hospitalization may be needed for severe cases requiring steroids, SSKI, or thionamides 6

Critical Pitfalls to Avoid

• Do not start levothyroxine during the hyperthyroid phase of subacute or postpartum thyroiditis—this worsens thyrotoxicosis 1, 2
• Do not assume hypothyroidism is permanent without reassessing thyroid function 3-6 months after the acute phase, as 70-80% of patients recover normal function 1, 2
• Do not miss acute suppurative thyroiditis—fever with severe neck pain requires urgent evaluation for bacterial infection and antibiotic treatment 5, 3
• Rule out adrenal insufficiency before starting levothyroxine in patients with suspected central hypothyroidism or hypophysitis, as thyroid hormone can precipitate adrenal crisis 7
• Do not order RAIU for Hashimoto thyroiditis or hypothyroidism workup—it adds no diagnostic value 6

Surveillance and Follow-Up

• All patients with thyroiditis require ongoing monitoring for changes in thyroid function, as permanent hypothyroidism can develop months to years after the acute episode 1, 2
• Recheck TSH and free T4 at 3 months, 6 months, and 12 months after diagnosis, then annually if stable 1, 2
• Patients with positive TPO antibodies have 4.3% annual risk of progression to overt hypothyroidism and warrant closer surveillance 8