# Thyroid Scintigraphy > Thyroid scintigraphy for NEET-PG Radiology: hot versus cold nodules, Graves versus thyroiditis uptake patterns and radioiodine therapy principles. - Canonical URL: https://prepelephant.com/topics/neet-pg/radiology/thyroid-scintigraphy - Exam / course: NEET-PG · Subject: Radiology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Thyroid Scintigraphy", PrepElephant, https://prepelephant.com/topics/neet-pg/radiology/thyroid-scintigraphy ## Direct answer Thyroid scintigraphy classifies thyrotoxicosis and characterises nodules by uptake pattern. Technetium-99m pertechnetate (trapped by the gland but not organified) or iodine-123 is imaged 20-30 minutes or several hours after injection respectively: Graves disease shows diffuse intense uptake, toxic multinodular goitre shows patchy uptake with hot nodules suppressing the rest, and destructive thyroiditis — subacute, postpartal, amiodarone-induced type 2 — shows near-absent uptake, the single most therapeutic distinction in thyrotoxicosis because thyroiditis gets steroids or observation, not antithyroid drugs or radioiodine. Hot nodules are autonomous and almost never malignant; cold nodules require ultrasound and fine-needle aspiration. Iodine-131, a beta and gamma emitter with an eight-day half-life, treats hyperthyroidism and differentiated thyroid cancer but is absolutely contraindicated in pregnancy and breastfeeding. ## What you must remember - **Tracer logic:** pertechnetate is trapped by the sodium-iodide symporter but not organified — hence the rare "discrepancy nodule" that traps pertechnetate yet is cold on iodine imaging; iodine-123 is organified and more physiological but costlier. - **Thyrotoxicosis decision tree:** diffuse uptake equals Graves; patchy lumpy uptake equals toxic multinodular goitre; a single hot focus with suppressed background equals toxic adenoma; uptake near zero equals thyroiditis (or exogenous hormone, or recent iodine load). - **Nodule rule:** hot nodules are almost never malignant; cold nodules carry a roughly 5-15% malignancy risk in a palpable nodule and route to ultrasound with fine-needle aspiration. - **Amiodarone thyrotoxicosis:** type 1 (iodine-induced excess synthesis) shows increased uptake; type 2 (destructive thyroiditis) shows near-none — the split decides thionamide versus steroids. - **Radioiodine-131:** half-life about 8 days, beta emission for therapy plus 364 keV gamma for imaging; treats Graves, toxic nodular goitre and differentiated thyroid cancer ablation. - **Pregnancy and lactation:** absolute contraindication to I-131; a pregnancy test precedes therapy, and breastfeeding must stop (with a discard interval) before radioiodine administration. - **Superscan clue in thyroid cancer:** post-thyroidectomy I-131 whole-body scanning surveys for residual, nodal and distant disease, with stimulated thyroglobulin as its biochemical partner. - **Technique detail:** pertechnetate imaging at about 20-30 minutes; withholding of thyroid hormone and iodine-containing drugs (amiodarone, recent contrast) is a prerequisite for valid uptake measurement. ## Sorting one thyrotoxic patient A 34-year-old woman, six weeks postpartum, presents with palpitations, tremor and a mildly tender gland; T4 is high and TSH suppressed. The clinical fork is Graves disease versus postpartum (lymphocytic) thyroiditis, and the treatments are opposites — antithyroid drugs and perhaps radioiodine versus observation with beta-blockers. Scintigraphy with pertechnetate shows a gland almost invisible against background: uptake under 1-2%. That single image ends the argument — destructive thyroiditis releasing preformed hormone, managed expectantly, often transiting to a hypothyroid phase. Now replay the same scene with a diffuse, intensely hot gland, a bruit and orbitopathy: Graves, and the discussion moves to the duration of thionamides versus definitive radioiodine, with the parenthood caveat that I-131 is deferred in pregnancy planning and after a recent breastfeeding period. The thyroid uptake number, not the hormone panel alone, is what pivots management — which is why boards pair a "low-uptake thyrotoxicosis" stem with thyroiditis and a "high-uptake" stem with Graves as reliably as sunrise. ## The uptake-number viva Reading the hormone pattern as sufficient is the core error — thyrotoxicosis biochemistry cannot distinguish synthesis excess from destructive release; only uptake imaging (or TSH-receptor antibodies) can. The second slip is cold-nodule overreaction: a cold area on a scan is common (cysts, colloid nodules, haemorrhage compete with malignancy) and mandates ultrasound, not immediate surgery; scintigraphy triages, ultrasound and cytology diagnose. Third, the pertechnetate-versus-iodine subtlety: a nodule that appears warm on pertechnetate can be cold on iodine because trapping without organisation is possible — a classic physiological viva question. In Indian practice, remember the iodine-deficiency hinterland: multinodular goitres are common, and a dominant cold area within a long-standing goitre deserves scrutiny for malignancy rather than dismissal as degeneration. ## Frequently asked questions ### What uptake pattern distinguishes Graves disease from thyroiditis? Graves shows diffuse intense glandular uptake, while destructive thyroiditis (subacute, postpartum, amiodarone type 2) shows near-absent uptake because the gland is leaking, not synthesising, hormone. ### Why are hot thyroid nodules rarely malignant? Autonomously functioning nodules suppress TSH, and the hyperstimulatory environment needed for most differentiated carcinomas is absent — malignancy risk in a truly hot nodule is under about 1-4%. ### Which tracer is preferred for thyroid imaging and why? Iodine-123 for physiological uptake imaging (organified, lower dose) and technetium-99m pertechnetate for routine convenience (available, cheap, 20-30 minute imaging), with the caveat that pertechnetate is trapped but not organified. ### What are the two types of amiodarone-induced thyrotoxicosis on scanning? Type 1, iodine-induced hormone excess, shows normal or increased uptake; type 2, destructive thyroiditis, shows suppressed uptake — separating thionamide therapy from glucocorticoids. ### When is radioiodine-131 contraindicated? In pregnancy and breastfeeding, absolutely; also deferred with recent iodinated contrast exposure or antithyroid drug loading that would block uptake, and used cautiously where ophthalmopathy is active in Graves.