Subacute thyroiditis (de Quervain thyroiditis) is a painful, self-limiting inflammatory thyroid disease that typically follows an upper respiratory tract infection. A viral etiology is suspected and it is associated with HLA-Bw35. The disease classically progresses through three phases: thyrotoxic phase (hormone release from cell destruction), hypothyroid phase, and recovery phase. It is 4-5 times more common in women and peaks between ages 30-50. Erythrocyte sedimentation rate (ESR) is markedly elevated. Lesions may migrate within the thyroid over time (migrating pattern), which is a characteristic finding of the disease.
Age Range
30-50
Peak Age
40
Gender
Female predominant
Prevalence
Uncommon
Subacute thyroiditis is a granulomatous inflammatory process triggered by viral infection. The virus (Coxsackie, adenovirus, influenza, SARS-CoV-2, etc.) damages thyroid follicular cells, initiating follicular destruction. Colloid and thyroid hormones (T3/T4) are released into the bloodstream from destroyed follicles — this explains the early thyrotoxic phase. Histologically, giant cells (multinucleated giant cells) and granulomas form at the site of follicular damage. On imaging, these appear as focal hypoechoic areas because inflammatory infiltration and edema disrupt the homogeneous echo pattern of normal follicular architecture. Doppler vascularity is decreased because inflammation causes capillary-level compression and thrombosis — this is the distinguishing feature from hypervascular Graves disease. On nuclear medicine, Tc-99m and I-123 uptake is decreased because follicular damage impairs NIS (sodium-iodide symporter) function and TSH is suppressed during the destructive phase.
On serial ultrasound follow-ups, the hypoechoic inflammatory area migrates within the thyroid — a lesion initially seen in one lobe may appear in the contralateral lobe or a different region of the same lobe on subsequent follow-up. This migration pattern is specific to subacute thyroiditis and reflects the virus affecting different follicular regions sequentially.
Focal or patchy hypoechoic area is seen in one or more thyroid lobes. Borders are irregular and ill-defined — unlike a well-defined nodule, the transition between the inflammatory area and surrounding parenchyma is gradual and blurred. The affected area typically extends to the thyroid capsule. In the acute phase, the involved area appears swollen and enlarged. As the disease progresses, hypoechoic areas may migrate over time to the contralateral lobe or different regions of the same lobe (migrating pattern) — this is pathognomonic for subacute thyroiditis.
Report Sentence
Patchy hypoechoic area with ill-defined borders extending to the capsule in the [right/left] thyroid lobe, consistent with subacute thyroiditis when correlated with clinical and laboratory findings.
Color Doppler US demonstrates markedly decreased or absent vascularity in the affected hypoechoic area. Blood flow is dramatically reduced compared to normal thyroid parenchyma. This finding creates a pattern opposite to the 'thyroid inferno' pattern (diffuse increased vascularity) seen in Graves disease and is critically important in differential diagnosis. Unaffected thyroid parenchyma shows normal vascularity.
Report Sentence
Color Doppler examination shows markedly decreased vascularity in the hypoechoic area, a finding favoring subacute thyroiditis as opposed to Graves disease.
Tc-99m pertechnetate scintigraphy shows diffusely decreased uptake in the thyroid gland. In the acute/thyrotoxic phase, uptake is low throughout the entire gland, which may appear faint or non-visualized. Focal involvement may be encountered: more pronounced decrease in affected areas with relatively preserved (but still decreased) activity in unaffected areas. Total thyroid uptake may drop below 1% (normal 0.3-3%). This finding paradoxically shows low uptake during a period of elevated serum thyroid hormones — a pathognomonic finding for destructive thyrotoxicosis.
Report Sentence
Tc-99m pertechnetate scintigraphy shows diffusely markedly decreased uptake in the thyroid gland, consistent with destructive thyrotoxicosis/subacute thyroiditis when correlated with elevated serum thyroid hormone levels.
I-123 thyroid uptake test shows diffusely low RAIU (radioactive iodine uptake); typically below 5%, often in the 1-2% range (normal 24-hour RAIU: 10-30%). This finding parallels the low uptake on Tc-99m scintigraphy. I-123 shows high uptake in Graves disease (40-80%) but is very low in subacute thyroiditis — this is the gold standard for differentiating destructive from stimulatory thyrotoxicosis.
Report Sentence
I-123 24-hour thyroid uptake measured at ...%, which is markedly low; consistent with destructive thyrotoxicosis (subacute thyroiditis) in the setting of thyrotoxicosis.
Non-contrast CT may show focal or patchy low-density areas in the thyroid gland. The normal thyroid is high density (80-120 HU) due to high iodine content; inflammatory areas lose this density due to follicular destruction and iodine depletion. Asymmetric gland enlargement and accompanying surrounding soft tissue edema are not uncommon. CT is not the primary modality for diagnosing subacute thyroiditis but may be detected incidentally on head and neck CT.
Report Sentence
Focal low-density area in the [right/left] lobe of the thyroid gland, raising the possibility of subacute thyroiditis requiring clinical correlation.
T2-weighted MR imaging shows focal or patchy hyperintensity in the affected thyroid area. Edema and inflammatory infiltration increase free water content, prolonging T2 relaxation time. Markedly increased signal is seen compared to normal thyroid parenchyma. On gadolinium-enhanced series, the affected area may show heterogeneous enhancement. MRI is not routinely used for diagnosing subacute thyroiditis but may be detected incidentally on head and neck MRI.
Report Sentence
Focal hyperintense area in the [right/left] thyroid lobe on T2-weighted sequences, consistent with an inflammatory process (possibility of subacute thyroiditis).
Criteria
Painful thyroid swelling, elevated ESR, typical triphasic clinical course (thyrotoxicosis → hypothyroidism → recovery). Most common form.
Distinct Features
Focal hypoechoic area corresponding to the painful region on US, decreased vascularity on Doppler, elevated T3/T4 and low TSH with low RAIU in the thyrotoxic phase.
Criteria
Painless thyroid swelling, normal ESR, autoimmune basis (anti-TPO may be positive). In postpartum form, develops 2-6 months after delivery. Also termed lymphocytic thyroiditis.
Distinct Features
Diffuse mild heterogeneity on US, more diffuse and milder appearance instead of the distinct focal hypoechoic area of the classic form. Similar low uptake on scintigraphy but without pain.
Criteria
Recurring episodes of subacute thyroiditis after complete recovery from the initial episode. Occurs in 1-4% of patients. Higher recurrence rate has been associated with HLA-Bw35 positivity.
Distinct Features
Recurrent hypoechoic areas in previously healed regions or new locations on serial US follow-ups. Risk of permanent hypothyroidism increases with each episode (up to 15% especially after multiple recurrent episodes).
Distinguishing Feature
Hashimoto thyroiditis shows diffuse heterogeneity, micronodular pattern and increased vascularity. Anti-TPO and anti-thyroglobulin are elevated. In subacute thyroiditis, focal hypoechoic area, decreased vascularity, elevated ESR and migration pattern are distinguishing.
Distinguishing Feature
Graves disease shows diffuse increased vascularity (thyroid inferno), diffusely enlarged gland and high RAIU. In subacute thyroiditis, focal decreased vascularity, focal hypoechoic area and very low RAIU are distinguishing. Both can present with thyrotoxicosis but the mechanism differs (stimulatory vs destructive).
Distinguishing Feature
Papillary carcinoma presents as a well-defined or irregular solid hypoechoic nodule, may have microcalcifications, and may show taller-than-wide shape. Subacute thyroiditis appears as a patchy hypoechoic area rather than a nodule, has ill-defined borders, no microcalcifications, and migrates over time.
Distinguishing Feature
Thyroid lymphoma usually develops on a background of Hashimoto, forms a markedly hypoechoic mass, shows rapid growth and increased vascularity. In subacute thyroiditis, no mass forms, vascularity is decreased and elevated ESR with pain are prominent. Absence of Hashimoto history supports subacute thyroiditis.
Urgency
routineManagement
medicalBiopsy
Not NeededFollow-up
6-monthSubacute thyroiditis is usually a self-limiting disease resolving spontaneously in 2-6 months. In the acute phase, pain is controlled with NSAIDs or aspirin; in severe cases, short-course corticosteroids (prednisone 40 mg/day, gradual taper) are administered. Symptomatic treatment (beta-blockers) may be given during the thyrotoxic phase. Temporary thyroid hormone replacement may be needed during the hypothyroid phase. Permanent hypothyroidism may develop in 5-15% of patients, so 6-month follow-up is recommended. FNA is generally not needed — clinical, laboratory and US findings are diagnostic.
Subacute thyroiditis is a self-limiting disease. Symptomatic treatment with NSAIDs or prednisone is sufficient. 5-15% of patients may develop permanent hypothyroidism. Decreased uptake on thyroid scintigraphy aids diagnosis. FNA is usually not needed.