General Medicine
Thyroid Dysfunction
Thyroid dysfunction for MBBS: interpreting thyroid function tests, Graves and Hashimoto disease, antithyroid drugs, radioiodine and thyroid emergencies, mapped to NMC codes IM12.1 to IM12.15.
MedNext Academy | 3 min read
Thyroid Dysfunction
Thyroid dysfunction for MBBS: interpreting thyroid function tests, Graves and Hashimoto disease, antithyroid drugs, radioiodine and thyroid emergencies, mapped to NMC codes IM12.1 to IM12.15.
This chapter covers hypothyroidism and hyperthyroidism, from the interpretation of thyroid function tests and antibodies to the choice between drug, radioactive iodine and surgical therapy. It also addresses the endocrine emergencies of thyroid storm and myxoedema coma and the public health iodisation programme.
High-yield: Thyroid Dysfunction
- Thyroid-stimulating hormone is the most sensitive first-line test of thyroid function.
- Primary hypothyroidism shows a high thyroid-stimulating hormone with a low free thyroxine.
- Primary hyperthyroidism shows a suppressed thyroid-stimulating hormone with a raised free thyroxine.
- Hashimoto thyroiditis is the commonest cause of hypothyroidism in iodine-sufficient areas and is associated with anti-thyroid peroxidase antibodies.
- Graves disease is the commonest cause of hyperthyroidism and features a diffuse goitre, eye signs and thyroid receptor antibodies.
- A high radioactive iodine uptake suggests Graves disease or toxic nodular goitre, while a low uptake suggests thyroiditis.
- Levothyroxine is the treatment of choice for hypothyroidism, taken on an empty stomach.
- Antithyroid drugs such as carbimazole and propylthiouracil are used for hyperthyroidism, with propylthiouracil preferred in the first trimester.
- Definitive treatment of hyperthyroidism uses radioactive iodine or surgery when medical therapy fails or relapses.
- Thyroid storm is a life-threatening decompensation of hyperthyroidism needing intensive combined therapy.
- Myxoedema coma is severe decompensated hypothyroidism with hypothermia and reduced consciousness.
- Subclinical hypothyroidism is a raised thyroid-stimulating hormone with a normal free thyroxine.
- Iodine deficiency remains an important cause of goitre and hypothyroidism, addressed by the salt iodisation programme.
- Agranulocytosis is a rare but serious adverse effect of antithyroid drugs, so any fever or sore throat needs a blood count.
- Thyroid function should be checked in atrial fibrillation, unexplained weight change and fatigue.
Interpreting thyroid function
- **Primary hypothyroidism:** High thyroid-stimulating hormone, low free thyroxine; Hashimoto is commonest.
- **Primary hyperthyroidism:** Suppressed thyroid-stimulating hormone, high free thyroxine; Graves is commonest.
- **Uptake scan:** High uptake in Graves or toxic nodule; low uptake in thyroiditis.
- **Treatment:** Levothyroxine for hypothyroidism; antithyroid drugs, radioiodine or surgery for hyperthyroidism.
NMC competencies in this chapter
- **IM12.1:** Epidemiology and pathogenesis of thyroid dysfunction
- **IM12.3:** Hypothalamic-pituitary-thyroid axis and function testing
- **IM12.4:** Radioactive iodine uptake in diagnosis
- **IM12.9:** Ordering and interpreting diagnostic tests
- **IM12.11:** Interpretation of thyroid function tests
- **IM12.12:** Iodisation programmes of the Government of India
- **IM12.13:** Pharmacology of thyroxine and antithyroid drugs
- **IM12.15:** Thionamides, radioactive iodine and surgery in thyrotoxicosis
Frequently Asked Questions
Why is thyroid-stimulating hormone the first-line test?
It is the most sensitive marker of thyroid status, rising early in primary hypothyroidism and falling early in hyperthyroidism, often before the free thyroxine changes.
How does the radioactive iodine uptake help?
A high uptake suggests Graves disease or a toxic nodular goitre, whereas a low uptake suggests thyroiditis, which changes the treatment approach.
Which antithyroid drug is preferred in early pregnancy?
Propylthiouracil is preferred in the first trimester because carbimazole carries a higher risk of certain congenital malformations at this stage.
How does this chapter help for NEET-PG?
Test interpretation patterns, uptake findings, drug choices and the thyroid emergencies are common exam themes that map directly to questions.
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