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Exam Cram
Exam Cram
Cushing's syndrome = hypercortisolaemia, range of causes exist
Cushing's disease = pituitary adenoma secreting ACTH causing hypercortisolaemia
Hypercortisolaemia diagnosis: low dose dexamethasone test & measure cortisol or 24hr urinary cortisol
Localise the source with high dose dexamethasone and ACTH
Cushing's disease vs Cushing's Syndrome
Cushing's disease vs Cushing's Syndrome
Cushing's Syndrome = Hypercortisolaemia
Cushing's Disease = Pituitary adenoma causing hypercortisolaemia
Summary
Summary
Diagnose Hypercortisolaemia:
Perform 24hr urinary cortisol or
Low dose Dexamethasone suppresion test (random cortisol minimal role)
Investigate Aetiology:
High dose dexamethasone test measuring cortisol and ACTH
Low cortisol, low ACTH = Pituitary source (Cushings Disease)
Raised cortisol, low ACTH = Adrenal source
Raised cortisol, raised ACTH = Ectopic ACTH, likely cancer
Ectopic sources produce their own ACTH which stimulates adrenal glands to produce cortisol.
Adrenal tumours produce cortisol, suppressing the pituitary's ACTH.
Cushing's Syndrome
Cushing's Syndrome
Background
Background
Cushing Syndrome describes the hypercortisolaemia state
Causes include:
Iatrogenic- PMR, RA, Transplants (most management aims to be steroid sparing)
Pituitary increased ACTH production- puitary adenoma
Ectopic ACTH production- malignancy, classically SCLC
Adrenal increased cortisol production- adrenal hyperplasia, adrenal adenoma
Assessment
Assessment
Presentation
Lethargy
Weight gain (centrally)
Polyuria, polydipsia
Examination
Cushingoid appearance: moon face, central obesity, bruising, thin skin
Hypertension
Investigations
Na+ upper limit of normal & K+ lower limit of normal
Hyperglycaemia- new onset or poor control
Diagnosis
Diagnosis
Diagnostic Criteria:
Raised cortisol after low dose dexamethasone
Raised 24hr urinary cortisol OR
Management
Management
Investigate Aetiology:
High dose dexamethasone test & serum cortisol/ ACTH
Management, by Source
Management, by Source
Pituitary Source (Cushing's disease)
Adenocarcinoma
Low cortisol (& low ACTH)
MRI pituitary
Surgical referral ?excision
Adrenal source
Low ACTH, high cortisol
CTAP with contrast ?adrenal adenoma
Surgical referral ?excision
Ectopic:
High ACTH, high cortisol
CTCAP: malignant source
If cancerous source- likely require biopsy +/- oncology and endocrine consults
Deeper Dive
Deeper Dive
Ectopic cancers typically produce ACTH, stimulating adrenal gland. Interestingly the adrenal gland is not suppressed by a high dose dexamethasone test and listens to the ectopic ACTH instead.
A random or midnight cortisol have little downside but are of little diagnostic benefit.
PseudoCushing's
Chronic alcoholism causes induces CYP450, resulting in metabolism of dexamethasone. This results in incomplete suppression of cortisol with dexamethasone suppression. Pseudocushing's requires only lifestyle advice. A high dose dexamethasone or 24hr urinary cortisol level can be considered.
Links
Links
Written in 2024, updated 2026.
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