Hypothyroidism. This post will cover the points you need to know for your board exams as well as for teaching residents on the daily rounds. Please don't use the information here to treat your patients.
High TSH and low T4 are usually sufficient for diagnosis of primary hypothyroidism. If not treated, can progress into myxedema coma.
Hashimoto thyroiditis is the most common cause of hypothyroidism where anti-TPO are usually positive (more sensitive than anti-Tg). This might be associated with lymphoma.
Hypothyroidism may be associated with type 1 diabetes mellitus and hypoadrenalism.
Medications associated with hypothyroidism include: amiodarone, carbamazepine, lithium interleukin, interferon rifampin, phenytoin, phenobarbital, tyrosine kinase inhibitors (sunitinib, imatinib) and thalidomide.
If TSH is high and T4 is normal then this is subclinical hypothyroidism which just need follow up. Treat when TSH>10 or when pregnancy is present or desired.
If TSH and T4 are low then think about central hypothyroidism like hypopituitarism.
Euthyroid sick syndrome usually happens critical illness where TSH is initially low and T4 is low or normal then TSH becomes high transiently too.
Treatment consists mainly of replacement therapy by levothyroxine. Start with 100 mcg in young (TSH goal 0.5-3) and 25 mcg in older especially with cardiac disease (TSH goal 4-6). Dose increase might be needed in pregnancy.
Myxedema coma is usually treated with IV T4 300-500 mcg. If no response may use T3 10 mcg q8 hrs (may cause myocardial infarction due to increased myocardial oxygen consumption). If hypoadrenalism is suspected then administer IV hydrocortisone 100 mg q8 hrs to avoid adrenal crisis that can be ppted by IV thyroxine.
More about the topics from Dr Hurlock book.
The information in this post is not for patients and shouldn't be used in treating patients. Please refer to your doctor for medical advice.