Central Hypothyroidism Diagnosis and Treatment

Diagnostic Priorities

The American Society of Clinical Oncology recommends checking morning cortisol level, which is mandatory before any thyroid hormone treatment, to rule out hypopituitarism immediately 1, 2
The American College of Clinical Oncology suggests checking ACTH level, which will be low or inappropriately normal in central adrenal insufficiency, and free T4 level, which should also be low in central hypothyroidism 1, 2
Additional pituitary hormones such as LH, FSH, testosterone or estradiol, and prolactin should be checked to evaluate for broader pituitary dysfunction 2

The American Society of Clinical Oncology recommends never starting thyroid hormone before corticosteroids in central hypothyroidism, as this can precipitate life-threatening adrenal crisis 1, 2, 3
If cortisol is low or the patient is symptomatic, hydrocortisone 10-20 mg orally in the morning and 5-10 mg in early afternoon should be started, and if the patient is acutely ill, hydrocortisone 100 mg IV or dexamethasone 4 mg IV should be used immediately 1, 2
The American College of Clinical Oncology suggests waiting several days after starting corticosteroids before initiating thyroid hormone replacement, and starting levothyroxine at a dose that is titrated based on patient age and cardiac status 2, 4

The American Society of Clinical Oncology recommends monitoring free T4 and free T3 levels instead of TSH to assess adequacy of treatment in central hypothyroidism, with a target FT4 in the upper half of the normal range and FT3 in the normal range 2, 4
Biochemical markers of thyroid hormone action, such as lipids and liver enzymes, should be monitored to assess adequacy of replacement 2, 4

The American Society of Clinical Oncology recommends monitoring thyroid function tests every cycle for the first 3 months with anti-PD-1/PD-L1 therapy, and every cycle with anti-CTLA4 therapy, as late endocrine dysfunction can occur months after treatment 1
Endocrine consultation is strongly recommended for all patients with suspected central hypothyroidism to guide comprehensive pituitary evaluation and hormone replacement strategy 2