SN2
SHORT NOTE
5M
★ High-yield
Write a short note on Cushing syndrome.
Definition
Cushing syndrome = the clinical state produced by chronic excess of glucocorticoids from any cause.Cushing disease = the subset caused specifically by an ACTH-secreting pituitary adenoma.
Causes
| Type | Cause | ACTH |
|---|---|---|
| Iatrogenic | Exogenous steroid therapy — commonest of all | Low |
| ACTH dependent | Pituitary adenoma (Cushing disease, 70% of endogenous) | High |
| ACTH dependent | Ectopic ACTH — small cell lung carcinoma | Very high |
| ACTH independent | Adrenal adenoma or carcinoma | Low (suppressed) |
Clinical Features
- Fat redistribution — moon face, buffalo hump, truncal obesity with thin limbs
- Protein catabolism — proximal muscle wasting and weakness, thin skin, easy bruising, poor wound healing
- Purple striae over the abdomen — wide and violaceous, unlike the pale striae of obesity
- Metabolic — hyperglycaemia and frank diabetes, hyperlipidaemia
- Bone — osteoporosis → vertebral fracture, back pain
- CVS — hypertension (mineralocorticoid effect), oedema
- Immune — susceptibility to infection, poor inflammatory response
- Reproductive — hirsutism, acne, amenorrhoea, impotence
- CNS — depression, euphoria, psychosis, insomnia
- Pigmentation — only in ACTH-dependent causes
Investigations
- Screening — 24-hour urinary free cortisol; late-night salivary cortisol; overnight 1 mg dexamethasone suppression test
- Loss of the diurnal rhythm is an early and characteristic finding
- High-dose dexamethasone test — suppresses in pituitary disease, does not suppress in ectopic ACTH or adrenal tumour
- Plasma ACTH then separates ACTH-dependent from independent causes
Applied Aspects
- Treatment — transsphenoidal surgery for pituitary adenoma; adrenalectomy for adrenal tumour; taper exogenous steroids slowly
- Nelson syndrome — after bilateral adrenalectomy, loss of feedback allows the pituitary tumour to enlarge with marked pigmentation
- Distinguish from simple obesity — obesity has generalised fat, pale striae, normal muscle power and preserved diurnal rhythm
All questions in Endocrine System
- Q1Describe the synthesis, transport and actions of thyroid hormones. Explain the regulation of thyroid secretion. ★
- Q2Describe the source, synthesis, actions and regulation of insulin. Add a note on glucagon. ★
- Q3Enumerate the hormones of the adrenal cortex. Describe the actions and regulation of cortisol and aldosterone. ★
- Q4Describe the actions and regulation of growth hormone. Add a note on the disorders of its secretion. ★
- Q5Describe the regulation of plasma calcium. Explain the actions of parathyroid hormone, vitamin D and calcitonin. ★
- SN1Write a short note on hypothyroidism. Describe cretinism and myxoedema. ★
- SN2Write a short note on Cushing syndrome. ★
- SN3Describe the hormones of the adrenal medulla and their actions. Differentiate adrenaline from noradrenaline. ★
- SN4Write a short note on oxytocin. ★
- SN5Define diabetes mellitus. Give its diagnostic criteria, types and complications. ★
- SN6Write a short note on Addison disease. ★
- SN7Enumerate the thyroid function tests and describe their interpretation.