Master Specialist Endocrinology (END5492)
for DHA Speciality

Core Concepts

The endocrine system relies on complex feedback loops. Key axes include the **Hypothalamic-Pituitary-Adrenal (HPA) axis** (CRH → ACTH → Cortisol), regulating stress, metabolism, and immunity; the **Hypothalamic-Pituitary-Thyroid (HPT) axis** (TRH → TSH → T3/T4), controlling metabolism, growth, and development. **Calcium homeostasis** is governed by PTH (raises calcium), Calcitriol (Vit D, raises calcium), and Calcitonin (lowers calcium), affecting bone, kidney, and gut. **Glucose homeostasis** involves Insulin (lowers glucose) from pancreatic beta cells and Glucagon (raises glucose) from alpha cells. The **adrenal cortex** produces Aldosterone (mineralocorticoid), Cortisol (glucocorticoid), and sex hormones, while the **adrenal medulla** produces catecholamines (Epinephrine, Norepinephrine). The **pituitary gland** secretes GH, Prolactin, TSH, ACTH, FSH, LH, ADH, and Oxytocin, influencing various target organs.

Clinical Presentation

• **Pituitary:**
  • *Hypopituitarism:* Fatigue, weakness, reduced libido, menstrual irregularities, cold intolerance, headache, visual field defects.
  • *Hyperpituitarism (e.g., Acromegaly, Cushing's Disease, Hyperprolactinemia):* Coarsening features, large hands/feet, central obesity, striae, moon face, galactorrhea, amenorrhea, erectile dysfunction.
• **Thyroid:**
  • *Hypothyroidism:* Fatigue, weight gain, constipation, cold intolerance, bradycardia, dry skin, depression.
  • *Hyperthyroidism:* Weight loss, palpitations, tremor, heat intolerance, anxiety, goiter, exophthalmos (Graves' disease).
• **Adrenal:**
  • *Adrenal Insufficiency (Addison's):* Fatigue, weakness, weight loss, hyperpigmentation, hypotension, hyponatremia, hyperkalemia.
  • *Cushing's Syndrome:* Central obesity, moon face, buffalo hump, striae, hypertension, hyperglycemia, muscle weakness.
  • *Primary Hyperaldosteronism (Conn's):* Hypertension, hypokalemia, muscle weakness, polyuria.
  • *Pheochromocytoma:* Paroxysmal hypertension, palpitations, headache, sweating, anxiety.
• **Parathyroid:**
  • *Hypercalcemia (Hyperparathyroidism):* "Stones, bones, groans, psychiatric overtones." Fatigue, polyuria, constipation, bone pain, depression.
  • *Hypocalcemia:* Paresthesias, muscle cramps, tetany, seizures (Chvostek's/Trousseau's signs).
• **Pancreatic (Diabetes Mellitus):** Polyuria, polydipsia, polyphagia, weight loss (Type 1), blurred vision, recurrent infections, numbness/tingling.

Diagnosis (Gold Standard)

Pituitary: MRI sella for anatomical assessment. Dynamic testing: Insulin Tolerance Test (ITT) for GH/cortisol deficiency; Oral Glucose Tolerance Test (OGTT) for GH excess; overnight 1mg dexamethasone suppression test or 24hr urinary free cortisol for Cushing's syndrome; serum Prolactin level.
Thyroid: TSH, FT4, FT3. Autoantibodies (TRAb for Graves', TPO/TgAb for Hashimoto's). Thyroid ultrasound for morphology/nodules; Scintigraphy for hyperthyroidism etiology.
Adrenal Insufficiency: Short Synacthen (ACTH stimulation) test.
Cushing's Syndrome: Low-dose dexamethasone suppression test (LDDST), 24hr urinary free cortisol (UFC), or late-night salivary cortisol.
Primary Hyperaldosteronism: Aldosterone-Renin Ratio (ARR). Confirmed by saline suppression test or fludrocortisone suppression test.
Pheochromocytoma: 24hr urinary fractionated metanephrines and normetanephrines, or plasma free metanephrines.
Parathyroid: Intact PTH, corrected calcium, phosphate, 25-hydroxyvitamin D. Sestamibi scan and/or ultrasound for localization.
Diabetes Mellitus: Fasting plasma glucose ≥7.0 mmol/L, HbA1c ≥6.5% (48 mmol/mol), or 2hr post-glucose load ≥11.1 mmol/L (OGTT).

Management (First Line)

Pituitary: Transsphenoidal surgery (TSS) for most functional adenomas. Hormone replacement for deficiencies (hydrocortisone, levothyroxine, testosterone, desmopressin). Dopamine agonists (bromocriptine/cabergoline) for hyperprolactinemia. Somatostatin analogs (octreotide/lanreotide) or GH receptor antagonists (pegvisomant) for acromegaly.
Thyroid:

• *Hypothyroidism:* Levothyroxine replacement.
• *Hyperthyroidism:* Anti-thyroid drugs (carbimazole/methimazole, PTU), radioiodine therapy, or surgery (thyroidectomy).

• *Insufficiency:* Glucocorticoid (hydrocortisone) and mineralocorticoid (fludrocortisone) replacement.
• *Cushing's:* Surgery (TSS for disease, adrenalectomy for syndrome). Medical therapy (ketoconazole, metyrapone).
• *Primary Hyperaldosteronism:* Adrenalectomy for unilateral adenoma. Spironolactone/Eplerenone for bilateral hyperplasia.
• *Pheochromocytoma:* Alpha-blockade (phenoxybenzamine) followed by beta-blockade, then surgical resection.

Exam Red Flags