THYROIDITIS

✓ Medically ReviewedDISEASEID: MDBT0289🚨 TRIAGE: URGENTICD-10: E06

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Definition

CLINICAL DEFINITION

Thyroiditis is a broad term encompassing inflammatory diseases of the thyroid gland, which may be acute, subacute, or chronic. The major forms include acute suppurative thyroiditis (usually bacterial), subacute thyroiditis (presumed viral, also called de Quervain's thyroiditis), and chronic autoimmune (Hashimoto's) thyroiditis. Each subtype has distinct aetiology, clinical course, and thyroid function test patterns.

IN PLAIN ENGLISH

Thyroiditis means inflammation of the thyroid gland. It is not a single disease; it includes several different conditions with different causes, such as infection, a viral trigger, or an autoimmune reaction. The type of thyroiditis determines whether the thyroid becomes overactive, underactive, or remains normal.

COMMON MISCONCEPTION / WHAT IT DOES NOT MEAN

Thyroiditis is NOT a single uniform disease. It is a category of distinct inflammatory conditions. For example, subacute thyroiditis is not treated with antithyroid drugs because the thyrotoxic phase is due to release of preformed hormone, not increased synthesis. Chronic autoimmune thyroiditis is not primarily an acute infection.

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Word Breakdown

thyr-

=thyroid (from Greek 'thyreos' — shield, referring to the shape of the thyroid cartilage)

-itis

=inflammation (from Greek '-itis')

Literal Meaning: Inflammation of the thyroid gland

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Abbreviations

SAT=Subacute Thyroiditis — also known as de Quervain's thyroiditis; the most common painful form.

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Synonyms & Variants

Inflammation of the Thyroid Gland›

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Category-Specific Context

Thyroiditis is a Disease category term that encompasses several distinct inflammatory entities. The primary classification separates painful from painless forms, and acute, subacute, and chronic temporal patterns. The most clinically relevant subtypes are acute suppurative thyroiditis (bacterial, surgical emergency risk), subacute thyroiditis (viral-triggered, triphasic, self-limited), and chronic autoimmune (Hashimoto's) thyroiditis (leading cause of hypothyroidism in iodine-sufficient regions).

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Clinical Context & Usage

CLINICAL SETTINGS

Endocrinology Outpatient ClinicGeneral Medicine WardEmergency DepartmentPrimary CareGeneral Surgery Ward

USAGE & DOCUMENTATION NOTES

In clinical documentation, 'thyroiditis' is almost always qualified by subtype (e.g., 'subacute thyroiditis', 'Hashimoto's thyroiditis', 'acute suppurative thyroiditis'). Unqualified use usually refers to the subacute form in acute presentations or to chronic autoimmune thyroiditis in the context of hypothyroidism. Thyroid function tests are documented alongside inflammatory markers (ESR, CRP) and thyroid autoantibodies (TPO, Tg) to characterise the phase and subtype.

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Primary Causes & Pathophysiology

PATHOPHYSIOLOGY

Thyroiditis involves disruption of thyroid follicular architecture by inflammatory processes. In subacute thyroiditis, a presumed viral trigger leads to granulomatous inflammation, follicular cell damage, and release of preformed thyroid hormones, causing an initial thyrotoxic phase; this is followed by a hypothyroid phase as hormone stores are depleted, and usually recovery. In chronic autoimmune (Hashimoto's) thyroiditis, lymphocytic infiltration and autoantibodies against thyroid peroxidase (TPO) and thyroglobulin progressively destroy follicular cells, often culminating in permanent hypothyroidism. In acute suppurative thyroiditis, bacterial infection causes frank abscess formation and necrosis. The resulting thyroid function derangement depends on the subtype and phase of the inflammatory process.

PRIMARY CAUSES

Viral infection or post-viral inflammatory response (Subacute Thyroiditis / de Quervain's)

Presumed viral trigger initiates granulomatous inflammation of the thyroid, disrupting follicles and releasing stored thyroid hormones; the gland is painful and tender.

Autoimmune lymphocytic infiltration (Hashimoto's Thyroiditis / Chronic Lymphocytic Thyroiditis)

Cell-mediated and antibody-mediated destruction of thyroid follicular cells, commonly with anti-TPO antibodies, leading to progressive glandular failure and often permanent hypothyroidism.

Bacterial infection (Acute Suppurative Thyroiditis)

Direct bacterial invasion of the thyroid gland, often via a pyriform sinus fistula or haematogenous spread, causing acute inflammation, abscess formation, and systemic illness.

Postpartum immune reconstitution (Postpartum Thyroiditis)

Immune system rebound after the immunosuppression of pregnancy triggers transient autoimmune thyroid inflammation, typically with a thyrotoxic phase followed by hypothyroidism and often recovery.

Drug-induced (e.g., interferon-alpha, amiodarone, immune checkpoint inhibitors)

Certain drugs can induce destructive thyroiditis through direct toxicity or immune-mediated mechanisms; the clinical pattern may be painless and variant.

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Drug-Induced Causes

💊 Interferon-alpha ↗

Mechanism: Immune-mediated thyroiditis, often with autoimmune features; can cause both destructive thyrotoxicosis and subsequent hypothyroidism.

→ Monitor thyroid function before and during therapy; manage thyrotoxicosis symptomatically and replace thyroid hormone if hypothyroidism develops.

💊 Amiodarone ↗

Mechanism: High iodine content and direct cytotoxicity can cause destructive thyroiditis (type 2 amiodarone-induced thyrotoxicosis), distinct from iodine-induced hyperthyroidism (type 1).

→ Differentiate type 1 versus type 2 AIT; type 2 may respond to glucocorticoids; continue or discontinue amiodarone based on risk-benefit and cardiology input.

💊 Immune checkpoint inhibitors (e.g., pembrolizumab, nivolumab, ipilimumab) ↗

Mechanism: Immune activation can lead to painless autoimmune thyroiditis, often presenting as hypothyroidism; thyrotoxicosis may occur transiently.

→ Monitor TSH and free T4 during treatment; levothyroxine replacement for hypothyroidism; hold or continue immunotherapy based on severity and oncology guidance.

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Epidemiology

Prevalence:Thyroiditis encompasses several subtypes with distinct epidemiology. Subacute thyroiditis is estimated to account for up to 5% of all clinical thyroid abnormalities and occurs at roughly 1 case per 5 cases of Graves' disease. Chronic autoimmune (Hashimoto's) thyroiditis is the most common cause of hypothyroidism in iodine-sufficient regions, with anti-TPO antibodies present in up to 30% of women over 80 years in some populations.

Age Group:Subacute thyroiditis most commonly affects adults aged 40–50 years and is rare in children. Chronic autoimmune thyroiditis is most frequently diagnosed in middle-aged women (ages 30–50), though it can occur at any age. Acute suppurative thyroiditis is rare and may occur in children or adults with predisposing anatomical factors.

Sex Predilection:Female

Geographic Distribution:The distribution of thyroiditis subtypes varies with iodine intake and autoimmune disease prevalence. Chronic autoimmune thyroiditis is more common in iodine-sufficient regions, while subacute thyroiditis occurs worldwide without a clear geographic predilection, though seasonal clustering has been reported in some series.

Red Flags & Triage ★

TRIAGE LEVEL

🚨 URGENT

DO NOT MISS — LIFE-THREATENING PRESENTATIONS

Acute suppurative thyroiditis with abscess formation or deep neck space extension — suggested by high fever, severe neck pain, systemic toxicity, and imaging showing a fluid collection; requires urgent surgical drainage and intravenous antibiotics.
Thyroid storm in the thyrotoxic phase of destructive thyroiditis — suggested by marked tachycardia, fever, agitation, and multi-organ decompensation; requires emergency supportive care and treatment of the underlying thyroiditis.

URGENT EVALUATION TRIGGERS

High fever (≥38.5°C) with severe neck pain and systemic toxicity — raises concern for acute suppurative thyroiditis or abscess.
Rapidly enlarging neck mass with stridor, dysphagia, or vocal changes — requires urgent evaluation for compressive haematoma, abscess, or malignancy.
Haemodynamic instability or altered mental status in a patient with thyrotoxicosis — raises concern for thyroid storm.

Contraindications & Precautions

CONTRAINDICATIONS

Antithyroid drugs (e.g.
methimazole
propylthiouracil) are contraindicated in the thyrotoxic phase of destructive thyroiditis (subacute
painless
amiodarone type 2) because the thyrotoxicosis is due to hormone release
not synthesis.

SPECIAL PRECAUTIONS

Differentiate destructive thyrotoxicosis (low radioactive iodine uptake) from Graves' disease (high uptake) before initiating antithyroid drug therapy; inappropriate use of antithyroid drugs in thyroiditis is ineffective and exposes the patient to unnecessary adverse effects.
In acute suppurative thyroiditis
obtain cultures and imaging to identify abscess or fistula before or alongside antibiotic therapy; do not delay drainage of a fluctuant abscess.
Monitor for permanent hypothyroidism after any episode of thyroiditis
as the need for levothyroxine may emerge months to years later.

Complications

DOWNSTREAM CLINICAL COMPLICATIONS

Permanent hypothyroidism — most characteristic of chronic autoimmune thyroiditis
but can occur after subacute thyroiditis in a minority of patients
Recurrence — subacute thyroiditis recurs in approximately 4% of patients
typically years after the initial episode
Abscess formation and deep neck space infection — in acute suppurative thyroiditis
requiring drainage and antibiotics
Thyroid storm — rare
but can occur in the thyrotoxic phase of any destructive thyroiditis
particularly if unrecognised

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Confused With (LASA & DDx) ★

LEXICAL (LASA) — SIMILAR NAMES

Thyroidosis

A non-standard or misspoken term; 'thyroidosis' is not a recognised diagnosis. Thyroiditis refers to inflammation, whereas thyrotoxicosis refers to the clinical syndrome of excess thyroid hormone.

CLINICAL DIFFERENTIAL DIAGNOSES (DDx)

Graves' Disease

Key Distinguishing Feature: Graves' disease causes thyrotoxicosis with diffusely increased radioactive iodine uptake (RAIU), positive TSH-receptor antibodies (TRAb), and often ophthalmopathy; subacute thyroiditis typically has low RAIU and a painful, tender gland.

Toxic Multinodular Goitre

Key Distinguishing Feature: Thyrotoxicosis with nodular goitre and focal or patchy increased RAIU; the gland is usually non-tender, and there is no triphasic course.

Haemorrhage into a Thyroid Nodule

Key Distinguishing Feature: Sudden painful neck swelling with a known nodule; thyroid function is usually normal and there is no systemic inflammatory response or thyrotoxic phase.

Anaplastic Thyroid Carcinoma

Key Distinguishing Feature: Rapidly enlarging, hard, fixed mass, often with compressive symptoms and vocal cord palsy; it may mimic thyroiditis ('pseudothyroiditis') but lacks the typical inflammatory marker elevation and triphasic thyroid function course.

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Clinical Pearls

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The triphasic course of subacute thyroiditis (thyrotoxicosis → hypothyroidism → recovery) can be diagnostically misleading if only a single thyroid function test is obtained; serial testing and a low radioactive iodine uptake during the thyrotoxic phase are key to distinguishing it from Graves' disease.

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Antithyroid drugs are not indicated for the thyrotoxic phase of destructive thyroiditis; beta-blockers are used for symptom control because the excess hormone is released from a damaged gland, not synthesised de novo.

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In acute suppurative thyroiditis, a pyriform sinus fistula should be considered as a predisposing anatomical tract, especially in children or recurrent cases; identification may require contrast study or endoscopy.

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Postpartum thyroiditis can be easily mistaken for postpartum depression or normal physiological changes; screening with TSH is appropriate if symptoms suggest thyroid dysfunction in the postpartum period.

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Example Usage & SOAP

CLINICAL SENTENCE

"A 42-year-old woman presents with a 2-week history of anterior neck pain radiating to the jaw, palpitations, and low-grade fever; examination reveals a tender, enlarged thyroid, and laboratory tests show suppressed TSH with elevated free T4 and a markedly elevated ESR."

IN A SOAP NOTE

S: 42-year-old female with anterior neck pain for 2 weeks, radiating to the right jaw, associated with palpitations and subjective fever. O: Temperature 37.9°C, heart rate 104 bpm, tender diffuse thyroid enlargement. Labs: TSH <0.01 mIU/L, free T4 32 pmol/L (elevated), ESR 68 mm/h, CRP 42 mg/L. RAIU scan: markedly reduced uptake. A: Subacute (de Quervain's) thyroiditis, thyrotoxic phase. P: Ibuprofen 400 mg PO q8h PRN for pain; propranolol 20 mg PO q8h for palpitations; repeat TFTs and ESR in 4 weeks; counsel on expected triphasic course and monitor for hypothyroid phase.

DIFFERENTIAL DIAGNOSIS CONTEXT

Differential for a painful thyroid with thyrotoxicosis: (1) Subacute thyroiditis — tender gland, elevated ESR/CRP, low RAIU, triphasic course; (2) Acute suppurative thyroiditis — high fever, systemic toxicity, abscess on ultrasound, usually normal TFTs; (3) Haemorrhage into a thyroid nodule — sudden pain, known nodule, normal TFTs and inflammatory markers; (4) Graves' disease — usually painless, high RAIU, positive TRAb; (5) Anaplastic carcinoma — hard fixed mass, rapid growth, compressive symptoms, no systemic inflammatory response.

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Prognosis

SHORT-TERM OUTCOME

Subacute thyroiditis is typically self-limited, with a triphasic course (thyrotoxicosis → hypothyroidism → recovery) over weeks to months; symptoms are manageable with NSAIDs or glucocorticoids and beta-blockers. Acute suppurative thyroiditis requires prompt antibiotics and drainage and can be life-threatening if untreated. Chronic autoimmune thyroiditis is slowly progressive over years.

LONG-TERM PROGNOSIS

After subacute thyroiditis, permanent hypothyroidism occurs in approximately 15% of patients after 28 years of follow-up in cohort data, and recurrence occurs in about 4%. Chronic autoimmune (Hashimoto's) thyroiditis frequently leads to permanent hypothyroidism requiring lifelong levothyroxine. Postpartum thyroiditis carries a 20–40% risk of permanent hypothyroidism in long-term follow-up.

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References & Coding

ICD-10 DIAGNOSTIC CODE

E06

LITERATURE CITATIONS & GUIDELINES

[1]Japan Thyroid Association. Guidelines for the diagnosis of Graves' disease, hypothyroidism, painless thyroiditis, chronic thyroiditis (Hashimoto's thyroiditis), and subacute thyroiditis (acute phase). Thyroid Science. 2025.

[2]Effraimidis G, Kasotas A, Markantes GK, Karapanou O, Saltiki K, Michalaki M. How to manage subacute thyroiditis. Drugs Context. 2026;15:2026-4-6. doi:10.7573/dic.2026-4-6

[3]P Hoffman R. Thyroiditis. Medscape Drugs & Diseases. Updated August 06, 2024.

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