14 · Endocrine Diagnostics & Pharmacology

Workup: check TSH first. If low \u2192 RAIU (a \"hot\" autonomous nodule is rarely cancer). If normal/high \u2192 ultrasound \u00b1 fine-needle aspiration based on size and suspicious features (microcalcifications, hypoechoic, irregular margins, tall).
Cancers: Papillary (most common, best prognosis, lymphatic spread, psammoma bodies); Follicular (hematogenous); Medullary (parafollicular C cells \u2192 calcitonin ; MEN2/RET); Anaplastic (elderly, aggressive, poor prognosis).

Choosing the assay or dynamic test, the imaging, and the hormone drugs.

Tests & imaging

Test	Used for
TSH ± free T4	First-line thyroid screen; TSH is most sensitive
A1c / fasting glucose / OGTT	Diabetes diagnosis and monitoring
Dexamethasone suppression	Cushing (excess cortisol) — fails to suppress if autonomous
ACTH (cosyntropin) stimulation	Adrenal insufficiency — cortisol fails to rise
Aldosterone : renin ratio	Primary aldosteronism
Plasma/urine metanephrines	Pheochromocytoma
IGF-1 + OGTT (GH suppression)	Acromegaly
Water-deprivation test	Diabetes insipidus (central vs nephrogenic)
Imaging	Thyroid US ± FNA; RAIU for hyperthyroidism; pituitary/sellar MRI; adrenal CT

Hormone pharmacology

Drug	Use & pearls
Levothyroxine	Hypothyroidism; empty stomach, separate from Ca/iron; titrate by TSH; start low in cardiac/elderly
Methimazole / PTU	Hyperthyroidism; PTU in first-trimester pregnancy and thyroid storm (blocks peripheral conversion); watch agranulocytosis/hepatotoxicity
Insulin & oral hypoglycemics	See Diabetes; metformin first-line; SGLT2/GLP-1 for CV/renal benefit
Glucocorticoids	Replacement (hydrocortisone) or suppression; stress-dose in illness/surgery; taper to avoid adrenal crisis; monitor for Cushingoid effects/osteoporosis
Fludrocortisone	Mineralocorticoid replacement in primary adrenal insufficiency
Dopamine agonists	Cabergoline/bromocriptine for prolactinoma
Bisphosphonates	Osteoporosis, Paget, hypercalcemia of malignancy

⭐ Suppress to prove excess, stimulate to prove deficiency — and always interpret the target hormone together with its trophic hormone to localize the lesion (primary gland vs pituitary).