Hypothyroidism
Direct answer
Hypothyroidism is a clinical syndrome resulting from deficient thyroid hormone action, most often from primary gland failure. Diagnosis rests on thyroid function tests: raised TSH with a low free T4 in primary disease, and treatment is oral levothyroxine at about 1.6 micrograms/kg/day taken fasting. Hashimoto's thyroiditis is the commonest cause in iodine-replete settings; myxoedema coma — hypothermia with altered sensorium — is its emergency, treated with intravenous levothyroxine plus hydrocortisone.
What you must remember
- Test pattern: primary hypothyroidism shows high TSH with low free T4; subclinical disease shows high TSH with a normal free T4.
- Causes: Hashimoto's thyroiditis (anti-TPO positive) is commonest in iodine-replete populations; iodine deficiency, post-ablative states (radioiodine, surgery) and drugs (amiodarone, lithium) remain important in India.
- Clinical signature: fatigue, weight gain, cold intolerance, constipation, menorrhagia, dry skin, hoarseness, bradycardia, periorbital puffiness and delayed relaxation of ankle jerks.
- Laboratory associations: hyponatraemia, dyslipidaemia (raised LDL), elevated creatine kinase and anaemia — often normocytic, macrocytic if coexistent B12 deficiency.
- Treatment rules: levothyroxine 1.6 micrograms/kg/day, empty stomach, 30-60 minutes before food, separated from calcium and iron; start low (25-50 micrograms) in the elderly or those with cardiac disease, and recheck TSH after about six to eight weeks.
- Myxoedema coma: hypothermia, altered sensorium, bradycardia and hyponatraemia, usually precipitated by infection or cold; give hydrocortisone with intravenous levothyroxine and supportive care.
- Pregnancy: levothyroxine requirement rises; tight first-trimester TSH control (generally below 2.5 mIU/L) matters for foetal neurodevelopment.
Common confusion
The classic confusion is primary versus secondary (central) hypothyroidism: in central disease the TSH is low or inappropriately normal alongside a low free T4, pointing to pituitary pathology — treating such a patient with levothyroxine alone can unmask adrenal insufficiency, which is why hydrocortisone precedes thyroid hormone when central disease or myxoedema coma is suspected. Distinguish hypothyroid puffy facies from renal or cardiac oedema (myxoedema is typically non-pitting), hypothyroidism from sick euthyroid syndrome in systemic illness (low T3, TSH usually normal), and remember that subclinical disease needs treatment chiefly when TSH exceeds 10 mIU/L or pregnancy, goitre or symptoms are present.
Exam-focused takeaway
NEET-PG questions on hypothyroidism are built around interpretation and rules: a TSH/free T4 pair asking primary versus secondary, the drug of choice and its dose and timing, the pattern of associated laboratory abnormalities (high CK, hyponatraemia, high LDL) and menstrual history (hypothyroidism causes menorrhagia, the opposite of hyperthyroidism's oligomenorrhoea), and anti-TPO in Hashimoto's. Myxoedema coma stems test the management sequence — hydrocortisone with intravenous levothyroxine — and pregnancy questions test the increased dose requirement and first-trimester TSH target. Clinical photograph stems may show the coarse puffy facies or pretibial changes, and mechanism questions probe why levothyroxine is separated from iron and calcium (absorption interference).
Practise previous-year and exam-style hypothyroidism questions inside the PrepElephant app — topic-wise question banks, full-length mocks and revision tools that keep flagged questions in rotation.
Frequently asked questions
What is the commonest cause of hypothyroidism?
Hashimoto's thyroiditis in iodine-replete settings; iodine deficiency and post-ablative hypothyroidism remain important causes in India.
Which tests diagnose hypothyroidism?
TSH with free T4 — high TSH with low free T4 indicates primary disease; a low or normal TSH with low free T4 suggests central (secondary) disease.
How is levothyroxine taken?
Fasting, 30-60 minutes before breakfast, separated from calcium and iron supplements; dose about 1.6 micrograms/kg/day, started low in the elderly and in cardiac disease.
Why is hydrocortisone given in myxoedema coma?
Coexisting adrenal insufficiency is common, and thyroid hormone replacement can precipitate an adrenal crisis — hydrocortisone is given with intravenous levothyroxine.
When is subclinical hypothyroidism treated?
Usually when TSH exceeds 10 mIU/L, or earlier with a goitre, symptoms, positive antibodies or pregnancy.
Practise this in the PrepElephant app
Question banks, previous-year questions, mock tests and revision tools — for Hypothyroidism and Medicine. Free to start.