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 Fatigue and pallor with a low haemoglobin, and it frequently coexists rather than competes. A TSH of 24 with a low free T4 in a fit 38 year old does not account for the whole picture.
2. Chronic fatigue syndrome (CFS) Disabling fatigue with post-exertional malaise and entirely normal investigations. A TSH of 24 with a low free T4 in a fit 38 year old shows an abnormality instead.
3. Coeliac disease Fatigue with diarrhoea, weight LOSS and iron deficiency, and positive tissue transglutaminase antibodies. A TSH of 24 with a low free T4 in a fit 38 year old does not fit.
4. Hypothyroidism correct Correct. Raised TSH with a low free T4 is overt primary hypothyroidism, and the clinical picture, fatigue, weight gain, constipation, cold intolerance, dry skin and the slow-relaxing reflexes, matches it exactly. The slowed relaxation phase is the most specific physical sign.
5. Depression Low mood and anhedonia with normal thyroid function, and the overlap is why TSH is checked. A TSH of 24 with a low free T4 in a fit 38 year old points to a physical cause.

The point: TSH is the screening test. High TSH with low free T4 is primary hypothyroidism; high TSH with normal free T4 is subclinical. Low TSH with low free T4 means the pituitary. Investigate, do not simply replace. Start levothyroxine at 1.6 micrograms/kg in the young and fit, but 25 micrograms in the elderly or in ischaemic heart disease, and recheck at 6 to 8 weeks. In pregnancy the dose needs increasing, 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 Hashimoto thyroiditis as the cause, which is the commonest in iodine-replete countries. It does not change today's treatment but it explains the disease and flags the associated autoimmune conditions worth watching for.
2. Serum cortisol Checked before replacement is started where adrenal insufficiency is possible, because thyroxine given first can precipitate an adrenal crisis. A TSH of 24 with a low free T4 in a fit 38 year old raises that question.
3. Full blood count Looks for the anaemia that commonly coexists and that also causes fatigue. A TSH of 24 with a low free T4 in a fit 38 year old makes it a sensible addition.
4. Free thyroxine Added to the TSH to separate overt from subclinical disease and to identify pituitary causes. A TSH of 24 with a low free T4 in a fit 38 year old makes it necessary.
5. MRI pituitary For low TSH with low free T4, which means the problem is above the thyroid. A TSH of 24 with a low free T4 in a fit 38 year old makes it necessary.

The point: TSH is the screening test. High TSH with low free T4 is primary hypothyroidism; high TSH with normal free T4 is subclinical. Low TSH with low free T4 means the pituitary. Investigate, do not simply replace. Start levothyroxine at 1.6 micrograms/kg in the young and fit, but 25 micrograms in the elderly or in ischaemic heart disease, and recheck at 6 to 8 weeks. In pregnancy the dose needs increasing, 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 Treats hyperthyroidism and would make this considerably worse. A TSH of 24 with a low free T4 in a fit 38 year old makes it the wrong direction.
2. Increase the levothyroxine dose Required in pregnancy, usually by 25 to 50%, and guided by trimester-specific TSH targets. A TSH of 24 with a low free T4 in a fit 38 year old makes it necessary.
3. Levothyroxine 1.6 micrograms/kg daily correct Correct. At 65 kg and 38 years old with no cardiac history, full replacement of about 100 micrograms daily can be started immediately. The cautious 25 microgram start is for the elderly and those with ischaemic heart disease, where a full dose risks precipitating angina.
4. Recheck thyroid function in 6 to 8 weeks TSH takes six to eight weeks to re-equilibrate after any dose change, so the follow-up interval is set by the physiology rather than by convenience. Testing at two weeks produces a number that prompts an unnecessary dose change, and a TSH of 24 with a low free T4 in a fit 38 year old here points elsewhere.
5. Levothyroxine 25 micrograms daily The cautious starting dose in the elderly or in ischaemic heart disease, where a full dose can precipitate angina or an arrhythmia. A TSH of 24 with a low free T4 in a fit 38 year old calls for that caution.

The point: TSH is the screening test. High TSH with low free T4 is primary hypothyroidism; high TSH with normal free T4 is subclinical. Low TSH with low free T4 means the pituitary. Investigate, do not simply replace. Start levothyroxine at 1.6 micrograms/kg in the young and fit, but 25 micrograms in the elderly or in ischaemic heart disease, and recheck at 6 to 8 weeks. In pregnancy the dose needs increasing, usually by 25 to 50%.

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