When patients present with symptoms of thyrotoxicosis include sweating palpitations, heat intolerance, weight loss despite good or increased appetite, and increased anxiety, they should still have biochemical screening to confirm the diagnosis. Initial management should be based on those test results.
If thyroid stimulating hormone (TSH) is suppressed, and free T4/thyroxine level elevated, the recent Society for Endocrinology guidelines suggest management based on free T4 levels:
Free T4 level between the upper limit of normal and 30 pmol/l
- Start carbimazole at a dose of 20 mg once daily and continue for six weeks
Free T4 30- 60 pmol/l
- Start carbimazole at a dose of 40 mg once daily and continue for six weeks
Free T4 is > 60 pmol/l
- Start carbimazole at a dose of 40 mg once daily and continue for the eight weeks
At the end of this, monitoring of thyroid function should be undertaken if available.
If not able to do the blood test, carbimazole should be increased to a dose of 40 mg once daily, with the addition of thyroxine therapy, in a ‘block and replace regimen’.
- Under 55 kg add thyroxine at a dose of 75 µg daily
- Over 55 kg, add thyroxine at a dose of 100 µg daily
Ideally if ongoing biochemical screening is available, a blood test including thyroid function, and full blood count with TSH receptor antibodies should be done six to eight weeks after initiating therapy with ongoing monitoring as per normal protocols. If not, this block and replace regimen, can be continued for up to six months.
If initial baseline hormonal screening is not available, and patients are being empirically treated on the basis of symptoms alone, a block and replace regimen using 40 mg of carbimazole and either 75/100 µg of thyroxine, based on body weight, can be initiated with resumption of thyroid function testing undertaken as soon as is practicable and referral to a local endocrine when services are available.
If the patient develops significant symptoms whilst being treated according to this algorithm, thyroid function must be tested, and the case discussed with an endocrinologist.
Any patient started on carbimazole should be informed of the potential side-effects, including agranulocytosis, as well as birth defects and abnormal liver function. Full blood count checks, must be done with sore throats, fevers, and infections of any sort with carbimazole discontinued until the white cell count is normal.
Anti-thyroid drugs (carbimazole and propthyouracil) are not known to increase the risk of infection with coronavirus, or to increase the risk of developing more severe disease in the event of contracting this disease. But, in view of the potentially rare side-effect of neutropenia close monitoring is sensible.
More details can be found at https://www.endocrinology.org/clinical-practice/covid-19-resources-for-managing-endocrine-conditions.
Dr Mustafa Al-Ansari is a specialist registrar in endocrinology and Professor Kevin Shotliff is consultant physician in endocrinology and diabetes at Chelsea and Westminster Hospital NHS Foundation Trust