Endocrine System
Pituitary and sodium
Prolactinoma causes amenorrhea, galactorrhea, and bitemporal hemianopia. SIADH produces euvolemic hyponatremia with low serum osmolality, high urine osmolality, and urine sodium above 40; treat with fluid restriction. Diabetes insipidus produces hypernatremia with inappropriately dilute urine; central disease responds to desmopressin.
Thyroid
Primary hypothyroidism: high TSH with low free T4; anti-TPO supports Hashimoto. Subclinical hypothyroidism: high TSH with normal free T4. Central hypothyroidism: low TSH with low free T4. Graves disease: diffuse goiter, ophthalmopathy, pretibial myxedema, TSH receptor antibodies. Thyroid storm presents with fever, delirium, and tachyarrhythmia; give a thionamide first, then a beta-blocker, then iodine (iodine must follow the thionamide).
Adrenal
Cushing syndrome: central obesity, striae, proximal weakness; screen with late-night salivary cortisol, 24-hour urine free cortisol, or overnight dexamethasone suppression, then use ACTH to separate ACTH-dependent from adrenal causes. Primary hyperaldosteronism: hypertension with hypokalemia, elevated aldosterone with suppressed renin. Addison disease: hyperpigmentation, hyperkalemia, hyponatremia, hypotension; confirm with cosyntropin stimulation. Pheochromocytoma: episodic headache, sweating, palpitations; screen with plasma free metanephrines.
Diabetes
Type 1: autoantibodies, lean habitus, ketosis-prone. Type 2: insulin resistance, acanthosis nigricans. DKA: glucose usually above 250, anion gap acidosis, ketones, Kussmaul respirations. HHS: very high glucose, high osmolality, minimal ketones. In DKA, give fluids first, then insulin, and replace potassium once it is below 5.2.
Rule of thumb
Correct total calcium for albumin: add 0.8 mg/dL to the measured calcium for every 1 g/dL that albumin is below 4.