Endocrine, diabetes and metabolic for PLAB 1

A 38 year old woman has six months of fatigue, weight gain, constipation and cold intolerance. Her skin is dry and her ankle reflexes are slow to relax. Her TSH is 24 mU/L and free T4 is 7 pmol/L. She has no cardiac history and weighs 65 kg. What is the SINGLE most likely diagnosis?

1. Anaemia Tiredness and pale skin with a low haemoglobin. This often exists alongside hypothyroidism rather than instead of it. That does not match a TSH of 24 with a low free T4 in a fit 38 year old.
2. Chronic fatigue syndrome (CFS) Disabling tiredness that gets worse after physical or mental effort, with every test coming back normal. It does not fit a TSH of 24 with a low free T4 in a fit 38 year old.
3. Coeliac disease Tiredness with diarrhoea, weight LOSS and low iron, with a positive blood test for tissue transglutaminase antibodies. But a TSH of 24 with a low free T4 in a fit 38 year old does not point to it.
4. Hypothyroidism correct Correct. A raised TSH with a low free T4 is a clearly underactive thyroid, and the whole picture, tiredness, weight gain, constipation, feeling the cold, dry skin and reflexes that relax slowly, fits exactly. That slow relaxation phase is the most specific physical sign to look for.
5. Depression Low mood and losing interest in things that used to be enjoyable (anhedonia), with normal thyroid tests. The overlap in symptoms is exactly why TSH gets checked. Here, a TSH of 24 with a low free T4 in a fit 38 year old points elsewhere.

The point: TSH (thyroid stimulating hormone, made by the pituitary gland to control the thyroid) is the test to start with. A high TSH with a low free T4 (the thyroid's own hormone) means the thyroid itself is underactive. A high TSH with a normal free T4 means mild, early underactivity that has not caused a hormone shortage yet (subclinical). A low TSH with a low free T4 points to a problem with the pituitary gland instead. Investigate properly rather than just starting treatment. Start levothyroxine (thyroid hormone replacement) at 1.6 micrograms per kilogram of body weight in someone young and fit, but only 25 micrograms in an elderly patient or someone with narrowed heart arteries (ischaemic heart disease), and recheck the blood test 6 to 8 weeks later. In pregnancy the dose needs to go up, usually by 25 to 50%.

Source: NICE NG145 — Thyroid disease: assessment and management NICE · tier 1, national regulator or guidance

A 38 year old woman has six months of fatigue, weight gain, constipation and cold intolerance. Her skin is dry and her ankle reflexes are slow to relax. Her TSH is 24 mU/L and free T4 is 7 pmol/L. She has no cardiac history and weighs 65 kg. What is the SINGLE most appropriate initial investigation?

1. Thyroid peroxidase antibodies correct Correct. Confirm the immune system attacking the thyroid (Hashimoto's thyroiditis) as the cause, the most common cause in countries with enough iodine in the diet. It does not change today's treatment, but it explains the disease and flags other autoimmune conditions worth watching for.
2. Serum cortisol Checked before starting thyroid hormone where the adrenal glands might also be underactive, because giving thyroxine first can trigger a dangerous adrenal crisis. Here, a TSH of 24 with a low free T4 in a fit 38 year old points elsewhere.
3. Full blood count Checks for the anaemia that commonly happens alongside hypothyroidism and that also causes tiredness. That does not match a TSH of 24 with a low free T4 in a fit 38 year old.
4. Free thyroxine Checked alongside the TSH to tell a full-blown thyroid problem from a mild, early one, and to spot a pituitary cause. But a TSH of 24 with a low free T4 in a fit 38 year old does not point to it.
5. MRI pituitary Used when the TSH is low and the free T4 is also low, which means the problem is above the thyroid, in the pituitary gland. It does not fit a TSH of 24 with a low free T4 in a fit 38 year old.

The point: TSH (thyroid stimulating hormone, made by the pituitary gland to control the thyroid) is the test to start with. A high TSH with a low free T4 (the thyroid's own hormone) means the thyroid itself is underactive. A high TSH with a normal free T4 means mild, early underactivity that has not caused a hormone shortage yet (subclinical). A low TSH with a low free T4 points to a problem with the pituitary gland instead. Investigate properly rather than just starting treatment. Start levothyroxine (thyroid hormone replacement) at 1.6 micrograms per kilogram of body weight in someone young and fit, but only 25 micrograms in an elderly patient or someone with narrowed heart arteries (ischaemic heart disease), and recheck the blood test 6 to 8 weeks later. In pregnancy the dose needs to go up, usually by 25 to 50%.

Source: NICE NG145 — Thyroid disease: assessment and management NICE · tier 1, national regulator or guidance

A 38 year old woman has six months of fatigue, weight gain, constipation and cold intolerance. Her skin is dry and her ankle reflexes are slow to relax. Her TSH is 24 mU/L and free T4 is 7 pmol/L. She has no cardiac history and weighs 65 kg. What is the SINGLE most appropriate immediate management?

1. Start carbimazole A drug that treats an overactive thyroid and would make this condition considerably worse. Here, a TSH of 24 with a low free T4 in a fit 38 year old points elsewhere.
2. Increase the levothyroxine dose Needed in pregnancy, usually by 25 to 50%, guided by TSH targets that change with each trimester. It does not fit a TSH of 24 with a low free T4 in a fit 38 year old.
3. Intravenous levothyroxine and hydrocortisone Given for myxoedema coma: low body temperature, a slow heart rate and reduced consciousness. But a TSH of 24 with a low free T4 in a fit 38 year old does not point to it.
4. Levothyroxine 25 micrograms daily The careful starting dose in an elderly patient or someone with narrowed heart arteries, where a full dose could trigger chest pain (angina) or an abnormal heart rhythm. That does not match a TSH of 24 with a low free T4 in a fit 38 year old.
5. Levothyroxine 1.6 micrograms/kg daily correct Correct. At 65 kg and 38 years old with no heart problems, full replacement of about 100 micrograms daily can be started straight away. The cautious 25 microgram starting dose is for the elderly and those with narrowed heart arteries, where a full dose risks triggering angina.

The point: TSH (thyroid stimulating hormone, made by the pituitary gland to control the thyroid) is the test to start with. A high TSH with a low free T4 (the thyroid's own hormone) means the thyroid itself is underactive. A high TSH with a normal free T4 means mild, early underactivity that has not caused a hormone shortage yet (subclinical). A low TSH with a low free T4 points to a problem with the pituitary gland instead. Investigate properly rather than just starting treatment. Start levothyroxine (thyroid hormone replacement) at 1.6 micrograms per kilogram of body weight in someone young and fit, but only 25 micrograms in an elderly patient or someone with narrowed heart arteries (ischaemic heart disease), and recheck the blood test 6 to 8 weeks later. In pregnancy the dose needs to go up, usually by 25 to 50%.

Source: NICE NG145 — Thyroid disease: assessment and management NICE · tier 1, national regulator or guidance