Thyroid Disorders
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Direct answer
Thyroid assessment in clinical practice begins with the TSH: a high TSH with low free T4 defines primary hypothyroidism, a low TSH with high free T4 defines primary hyperthyroidism, and both normal in the presence of symptoms argues against significant dysfunction. Hypothyroidism is treated with once-daily levothyroxine on an empty stomach, while Graves disease — the commonest cause of hyperthyroidism in young Indian women — is managed with a thionamide course, beta-blockade for symptoms and, in selected cases, radioiodine or surgery. India's iodisation programme under its iodine deficiency disorders control efforts has made simple goitre preventable, though autoimmune disease remains common.
What you must remember
- Interpretation ladder: TSH first, then free T4; a deranged TSH with normal free T4 is subclinical disease, treated only when the TSH is clearly raised (commonly above 10 mIU per litre), in pregnancy, or when symptoms are convincing.
- Levothyroxine is taken fasting, 45 to 60 minutes before breakfast, at a replacement dose near 1.6 micrograms per kg per day; iron, calcium and proton pump inhibitors interfere with absorption and must be separated.
- Graves disease: diffusely enlarged painless goitre, orbitopathy, pretibial myxoedema and thyroid acropachy; first-line in India is a 12-to-18 month thionamide course (carbimazole or methimazole), with propranolol for symptom control.
- Propylthiouracil is preferred in the first trimester of pregnancy and in thyroid storm; watch thionamides for agranulocytosis — a sore throat on treatment demands an urgent blood count.
- Thyroid storm presents with fever, tachyarrhythmia, agitation or coma and heart failure; treatment combines propylthiouracil, iodine (given at least an hour after the thionamide), beta-blockade, steroids and supportive care.
- Pregnancy raises levothyroxine needs by roughly 30 per cent; the first-trimester TSH target is below 2.5 mIU per litre, and untreated maternal hypothyroidism harms fetal neurodevelopment.
- Subacute (de Quervain) thyroiditis gives a tender goitre with a suppressed TSH, raised inflammatory markers and a poor tracer uptake, contrasting with the high uptake of Graves disease; it resolves with NSAIDs and steroids if needed.
Common confusion
Candidates confuse primary with central disease: a low TSH with a low free T4 points to pituitary failure, needing further pituitary work-up, not levothyroxine alone. The second trap is the nodular distinction — a toxic multinodular goitre or a hot nodule is not Graves disease and responds poorly to thionamides alone, favouring radioiodine. Finally, remember that a tender gland means thyroiditis, where antithyroid drugs are useless because the hyperthyroidism is destructive release, not synthesis.
Exam-focused takeaway
FMGE thyroid questions are interpret-and-prescribe: the TSH–T4 pattern names the disease, the empty-stomach levothyroxine rule answers dosing questions, and the young woman with goitre, eye signs and tremor is Graves disease treated with a thionamide. Learn the pregnancy target and the 30 per cent dose increase, the propylthiouracil-first rule in the first trimester, and the sore-throat agranulocytosis alarm. A fever-plus-arrhythmia stem is thyroid storm, where sequence matters: block synthesis, then iodine, then supportive therapy.
Frequently asked questions
How is levothyroxine taken correctly?
Fasting, 45 to 60 minutes before breakfast, with iron and calcium supplements separated by several hours because they block absorption.
What distinguishes Graves disease from other causes of hyperthyroidism?
Diffuse goitre with orbitopathy, pretibial myxoedema, TSH-receptor antibodies and a high radioiodine uptake, against the poor uptake of destructive thyroiditis.
Which antithyroid drug is used in the first trimester?
Propylthiouracil, because carbimazole and methimazole carry teratogenic risk; most women can switch back later in pregnancy.
What is the first-trimester TSH target in pregnancy?
Below about 2.5 mIU per litre, achieved by increasing the pre-pregnancy levothyroxine dose as soon as pregnancy is confirmed.
What marks thyroid storm?
Fever, marked tachyarrhythmia, agitation or coma with heart failure — treated with propylthiouracil, then iodine, beta-blockade and steroids.