Thyroiditis Pathology
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Direct answer
Ask two questions of any thyroiditis: is the gland painful, and what is the functional state? Pain points to suppurative thyroiditis or De Quervain subacute granulomatous thyroiditis — a post-viral, self-limiting illness with tender goitre, giant-cell granulomas, a high erythrocyte sedimentation rate and a thyrotoxic phase that settles without antithyroid drugs. Painless glands with thyrotoxicosis signal silent lymphocytic thyroiditis or its postpartum form, in which lymphocytic infiltration leaks stored hormone and a hypothyroid phase often follows before recovery. Chronic autoimmune Hashimoto thyroiditis remains the commonest overall, while drug-induced disease (amiodarone, lithium, checkpoint inhibitors) and Riedel thyroiditis — the woody, IgG4-related fibrosis that mimics carcinoma — complete the classification that professional examinations never tire of testing.
What you must remember
- Acute suppurative thyroiditis: staphylococcal or streptococcal infection of a child's gland, typically the left lobe, sometimes through a pyriform sinus fistula — the fistula connection is the detail that separates a viva pass from a stumble.
- De Quervain (subacute granulomatous) thyroiditis: painful tender goitre two to three weeks after a viral upper respiratory infection; non-caseating granulomas with multinucleated giant cells; erythrocyte sedimentation rate markedly raised; radioactive iodine uptake is low (destructive release) while thyroxine is high — the classic discordance.
- Silent and postpartum thyroiditis: painless lymphocytic thyroiditis with a triphasic course — thyrotoxicosis (weeks), hypothyroidism (months), recovery; postpartum thyroiditis affects roughly 5 to 10 per cent of Indian pregnancies by various series, and beta-blockers alone suffice in the toxic phase.
- Hashimoto thyroiditis: anti-thyroid peroxidase antibodies, lymphoplasmacytic infiltrate with germinal centres and oxyphilic Hürthle change; transient thyrotoxicosis at onset (hashitoxicosis) before hypothyroidism.
- Drug-induced disease: amiodarone (iodine-loaded) causes both type 1 excess synthesis and type 2 destructive thyroiditis — a distinction with opposite treatments; lithium, interferon and immune checkpoint inhibitors trigger painless thyroiditis or Hashimoto-like disease.
- Riedel thyroiditis: dense fibrosis replacing the gland and invading surrounding tissue, now grouped with IgG4-related disease; firm, fixed, painless — clinically indistinguishable from anaplastic carcinoma until biopsy.
- Steroid responsiveness marker: De Quervain and silent thyroiditis respond dramatically to corticosteroids; bacterial suppurative disease needs drainage and antibiotics, not steroids — a pairing examiners enjoy.
Sorting pain from silence, step by step
A 34-year-old woman, four months postpartum, presents with palpitations and a slightly enlarged, non-tender thyroid. Run the algorithm. First, the tenderness question separates her from De Quervain, where pain radiates to the jaw and the sedimentation rate soars. Second, check the uptake: her suppressed thyroid-stimulating hormone with high free thyroxine and a low radioactive iodine uptake (or a low technetium uptake) confirms destructive release, not Graves disease — the single most valuable discriminating test in thyrotoxicosis with goitre. Third, antibodies: strong anti-thyroid peroxidase titres favour postpartum (silent) thyroiditis; thyroid-stimulating immunoglobulins would redirect toward Graves, which can also present postpartum. Fourth, manage expectantly — beta-blockade for symptoms, no antithyroid drugs (they do nothing for a destroyed follicle's leaked hormone), monitoring into the hypothyroid phase, with levothyroxine if symptomatic or prolonged, and reassurance that most recover within a year while remaining at risk in future pregnancies.
Contrast the painful branch: the same four steps applied to a tender gland give De Quervain (viral prodrome, granulomatous histology, steroid-responsive), suppurative disease (fever, unilateral, fluctuant, pus on needle) or, rarely, haemorrhage into a nodule — sudden pain but a pre-existing lump and no fever.
Where the exam sets its traps
The commonest error is treating destructive thyrotoxicosis with carbimazole or propylthiouracil: in De Quervain, silent and postpartum thyroiditis the gland is a leaking storehouse, not an overactive factory, so antithyroid drugs are useless and the phase is self-limiting. The second is the amiodarone dichotomy — type 1 (iodine-induced hormone excess, treat with thionamides) versus type 2 (destructive thyroiditis, treat with steroids) — where giving the wrong treatment visibly worsens the patient. Third, Riedel thyroiditis masquerading as carcinoma: a stony-hard fixed gland warrants biopsy before labelling malignancy, and elevated serum IgG4 supports the fibroinflammatory diagnosis.
Frequently asked questions
Which thyroiditis follows a viral infection and shows granulomas?
De Quervain subacute granulomatous thyroiditis — painful, tender, with giant-cell granulomas and a markedly raised erythrocyte sedimentation rate.
Why is radioactive iodine uptake low in subacute and postpartum thyroiditis but high in Graves disease?
Destructive thyroiditis leaks stored hormone while damaged follicular cells cannot trap iodide, whereas Graves disease actively synthesises hormone with high uptake — the key discriminator of thyrotoxicosis.
What is hashitoxicosis?
Transient thyrotoxicosis at the onset of Hashimoto thyroiditis from disruption of follicles, typically resolving into hypothyroidism without antithyroid treatment.
How do the two amiodarone-induced thyroid diseases differ in treatment?
Type 1 (iodine-induced excess synthesis) receives thionamides, while type 2 (destructive thyroiditis) receives glucocorticoids — an opposite-treatment pair.
Which thyroiditis is linked to IgG4-related disease?
Riedel thyroiditis, a woody fibrosing process that invades perithyroidal tissue and responds to steroids rather than surgery.