Master thyroid disorders for NEET PG 2026: HPT axis, hypothyroidism, Hashimoto's, hyperthyroidism, Graves disease, thyroid storm, TFT interpretation, thyroid nodule evaluation, Bethesda system, thyroid cancers, and anti-thyroid drugs.
Version 1.0 — Published March 2026
Thyroid disorders contribute 3–5 questions per NEET PG paper across medicine, surgery, pathology, and pharmacology. Master these 8 high-yield areas:
Thyroid disorders are among the most integrated topics in NEET PG — tested from the medicine angle (clinical features, TFT interpretation), the surgery angle (nodule evaluation, cancer management), the pathology angle (histopathology of cancers), and the pharmacology angle (anti-thyroid drugs, levothyroxine dosing). A single thyroid vignette can test knowledge from four subjects simultaneously. The student who builds a complete mental model of thyroid physiology, dysfunction, and neoplasia captures marks across multiple papers.
This guide covers the full spectrum — from the HPT axis that underpins every TFT question to the Bethesda classification that determines surgical management. Pair this with practice on the Medicine subject hub and cross-reference the high-yield surgery topics for the operative thyroid content.
The hypothalamic-pituitary-thyroid (HPT) axis is the neuroendocrine feedback loop controlling thyroid hormone production — and understanding this loop is essential for interpreting every thyroid function test question in NEET PG.
This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
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Key facts for NEET PG:
The steps of thyroid hormone synthesis are tested as a standalone question — particularly the step each drug blocks:
Hypothyroidism is deficient thyroid hormone production — the most common thyroid disorder, affecting 4–10% of the adult population, with a female-to-male ratio of 5–8:1.
| Type | Location of defect | Common causes | TSH | Free T4 |
|---|---|---|---|---|
| Primary | Thyroid gland | Hashimoto's, iodine deficiency, post-thyroidectomy, post-radioiodine, drugs (lithium, amiodarone) | High | Low |
| Secondary | Pituitary | Pituitary adenoma, Sheehan syndrome, surgery, radiation | Low or normal | Low |
| Tertiary | Hypothalamus | Hypothalamic tumors, infiltrative disease | Low or normal | Low |
Hashimoto's thyroiditis (chronic lymphocytic thyroiditis) is the most common cause of hypothyroidism in iodine-sufficient areas — an autoimmune disorder with lymphocytic infiltration and gradual destruction of thyroid follicles.
Antibodies:
Pathology: Lymphocytic infiltration, germinal centers, Hurthle cell change (eosinophilic metaplasia of follicular cells)
Associations: Type 1 DM, Addison disease, pernicious anemia, celiac disease, Turner syndrome, Down syndrome
NBE point: Hashimoto's increases the risk of thyroid lymphoma (primary thyroid B-cell lymphoma, usually MALT lymphoma or DLBCL). A rapidly enlarging thyroid in a patient with long-standing Hashimoto's should raise suspicion.
Myxedema coma is the most severe and life-threatening manifestation of hypothyroidism — a medical emergency with 30–60% mortality.
Triggers: Infection, cold exposure, sedatives, surgery, trauma in a patient with untreated or undertreated hypothyroidism.
Clinical features: Hypothermia (<35 degrees C), altered consciousness progressing to coma, bradycardia, hypoventilation with CO2 retention, hyponatremia, hypoglycemia.
Management:
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Start Free Practice →Hyperthyroidism is excess thyroid hormone production or release — presenting with a hypermetabolic state of heat intolerance, weight loss, tremor, and tachycardia.
Graves disease is the most common cause of hyperthyroidism (60–80% of cases) — an autoimmune disorder caused by thyroid-stimulating immunoglobulins (TSI) that activate the TSH receptor.
Clinical triad (unique to Graves, NOT seen in other causes of hyperthyroidism):
Antibodies: TSI (thyroid-stimulating immunoglobulin) — pathogenic; anti-TPO often positive as well.
Radioiodine uptake scan: Diffusely increased uptake (differentiates from subacute thyroiditis where uptake is LOW).
| Feature | Graves disease | Toxic MNG | Toxic adenoma |
|---|---|---|---|
| Age | 20–40 years | >50 years | 30–50 years |
| Goiter | Diffuse, smooth | Nodular, irregular | Single nodule |
| Eye signs | Present (ophthalmopathy) | Absent | Absent |
| RAIU scan | Diffusely increased | Patchy hot and cold areas | Single hot nodule, rest suppressed |
| Antibodies | TSI positive | TSI negative | TSI negative |
| Treatment | ATDs, RAI, surgery | RAI or surgery | RAI or surgery |
Thyroid storm is a life-threatening exacerbation of hyperthyroidism — mortality 10–30% even with treatment.
Triggers: Surgery, infection, RAI therapy, iodinated contrast, trauma, DKA in a patient with uncontrolled hyperthyroidism.
Clinical features: Fever >40 degrees C, tachycardia >140 bpm, altered mental status (agitation → delirium → coma), cardiac failure, GI dysfunction (nausea, vomiting, diarrhea, jaundice).
Management (order matters):
TFT interpretation is a systematic approach to reading TSH and free T4/T3 levels — tested in every NEET PG paper, often as a table-matching question.
| Pattern | TSH | Free T4 | Free T3 | Diagnosis |
|---|---|---|---|---|
| Low | High | High | Primary hyperthyroidism (Graves, toxic nodule) | |
| High | Low | Low | Primary hypothyroidism (Hashimoto's, iodine deficiency) | |
| High | Normal | Normal | Subclinical hypothyroidism | |
| Low | Normal | Normal | Subclinical hyperthyroidism | |
| Low/normal | Low | Low | Secondary hypothyroidism (pituitary failure) | |
| High | High | High | TSH-secreting pituitary adenoma or thyroid hormone resistance | |
| Low | Low | High | T3 thyrotoxicosis (early Graves or toxic nodule) |
Subclinical hypothyroidism treatment criteria:
Euthyroid sick syndrome (non-thyroidal illness):
Thyroid nodule evaluation is the systematic assessment of thyroid nodules to exclude malignancy — 4–7% of the general population has palpable nodules, and 5–15% of these are malignant.
Initial workup:
| Category | Interpretation | Malignancy risk | Management |
|---|---|---|---|
| I | Non-diagnostic / unsatisfactory | 5–10% | Repeat FNAC |
| II | Benign (colloid nodule, thyroiditis) | 0–3% | Follow-up |
| III | Atypia of undetermined significance (AUS) / follicular lesion of undetermined significance (FLUS) | 10–30% | Repeat FNAC or molecular testing |
| IV | Follicular neoplasm / suspicious for follicular neoplasm | 25–40% | Diagnostic lobectomy |
| V | Suspicious for malignancy | 50–75% | Near-total thyroidectomy |
| VI | Malignant | 97–99% | Total thyroidectomy |
Key NBE point: FNAC cannot distinguish follicular adenoma from follicular carcinoma — the distinction requires demonstrating capsular or vascular invasion on histopathology, which needs surgical excision (lobectomy). This is why Bethesda IV mandates diagnostic lobectomy.
Thyroid cancer is the most common endocrine malignancy — classified by the cell of origin into differentiated (papillary, follicular), medullary (C cells), and anaplastic.
| Feature | Papillary | Follicular | Medullary | Anaplastic |
|---|---|---|---|---|
| Frequency | 80–85% | 10–15% | 3–5% | 1–2% |
| Age | Young adults | Middle-aged | Any age (MEN) | Elderly (>60) |
| Spread | Lymphatic (cervical LN) | Hematogenous (bone, lung) | Both | Local invasion |
| Histopathology | Orphan Annie eye nuclei, psammoma bodies, nuclear grooves | Capsular/vascular invasion | Amyloid stroma (Congo red+), calcitonin | Pleomorphic giant cells |
| Tumor marker | Thyroglobulin | Thyroglobulin | Calcitonin, CEA | None |
| RAI avid | Yes | Yes | No | No |
| Prognosis | Excellent (95% 10-yr) | Good (80% 10-yr) | Moderate (50% 10-yr) | Dismal (median 6 months) |
| Associated syndrome | Gardner syndrome | — | MEN 2A, MEN 2B | — |
Thyroid management in pregnancy is a high-yield area tested from both the medicine and obstetrics perspectives — with specific drug restrictions and screening criteria that NEET PG tests directly.
Physiological changes in pregnancy:
Hypothyroidism in pregnancy:
Hyperthyroidism in pregnancy:
Anti-thyroid drugs (thionamides) are the pharmacological agents used to treat hyperthyroidism — and the PTU vs methimazole comparison is one of the most predictable NEET PG pharmacology questions.
| Feature | Methimazole | PTU |
|---|---|---|
| Mechanism | Inhibits TPO (organification + coupling) | Inhibits TPO + blocks peripheral T4→T3 conversion |
| Dosing | Once daily | Three times daily |
| Potency | 10x more potent | Lower potency |
| First-line | Yes (all non-pregnant adults) | No (except first trimester and thyroid storm) |
| Pregnancy (1st trimester) | Contraindicated (teratogenic) | Preferred |
| Thyroid storm | Second choice | First choice (extra T4→T3 block) |
| Crosses placenta | More (longer half-life) | Less |
| Hepatotoxicity | Cholestatic pattern (mild) | Fulminant hepatic necrosis (rare but severe) |
| Agranulocytosis | 0.1–0.5% | 0.1–0.5% |
Agranulocytosis — the critical ADR:
Thyroid disorders contribute 3-5 direct questions per NEET PG paper across medicine, surgery, pathology, and pharmacology. TFT interpretation, Graves disease features, thyroid cancer classification, and anti-thyroid drug side effects are the four most frequently tested areas based on 2019-2025 analysis.
Low TSH with high T3/T4 indicates primary hyperthyroidism (Graves, toxic nodule). High TSH with low T3/T4 indicates primary hypothyroidism (Hashimoto's). Low TSH with low T3/T4 indicates secondary (pituitary) hypothyroidism. High TSH with normal T3/T4 is subclinical hypothyroidism. Always start with TSH — it is the most sensitive screening test.
Iodine deficiency remains the most common cause of hypothyroidism worldwide and in iodine-deficient regions of India. In iodine-sufficient areas, Hashimoto's thyroiditis (chronic autoimmune thyroiditis) is the most common cause. Anti-TPO antibodies are the most sensitive marker for Hashimoto's.
Papillary thyroid carcinoma accounts for 80-85% of all thyroid cancers. It has the best prognosis, spreads via lymphatics (cervical lymph nodes), and shows Orphan Annie eye nuclei and psammoma bodies on histopathology. The typical patient is a young female with a cold nodule on thyroid scan.
PTU is preferred over methimazole only in the first trimester of pregnancy (methimazole is teratogenic — aplasia cutis, choanal atresia) and in thyroid storm (PTU inhibits peripheral T4-to-T3 conversion in addition to blocking thyroid hormone synthesis). In all other situations, methimazole is preferred due to once-daily dosing and fewer side effects.
The Bethesda system classifies thyroid FNAC results into 6 categories: I (non-diagnostic, repeat FNAC), II (benign, follow-up), III (atypia of undetermined significance, repeat FNAC or molecular testing), IV (follicular neoplasm, diagnostic lobectomy), V (suspicious for malignancy, near-total thyroidectomy), VI (malignant, total thyroidectomy).
Graves disease presents in younger women (20-40 years) with diffuse goiter, exophthalmos, pretibial myxedema, and thyroid-stimulating immunoglobulin (TSI) positivity. Radioiodine uptake is diffusely increased. Toxic MNG presents in older patients (above 50) with nodular goiter, no eye signs, and patchy radioiodine uptake.
Myxedema coma is a life-threatening decompensation of severe hypothyroidism presenting with altered consciousness, hypothermia, bradycardia, hypoventilation, and hyponatremia. Treatment is IV levothyroxine loading dose (200-400 mcg), IV hydrocortisone (to prevent adrenal crisis before thyroid replacement), passive rewarming, and supportive care. Mortality is 30-60%.
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This content is for educational purposes for NEET PG exam preparation. It is not a substitute for professional medical advice, diagnosis, or treatment. Clinical information has been reviewed by qualified medical professionals.
Written by: NEETPGAI Editorial Team Reviewed by: Pending SME Review Last reviewed: March 2026
This article is reviewed by qualified medical professionals for clinical accuracy and exam relevance. For corrections or updates, contact the editorial team.