Cushing's Syndrome Diagnosis and Management

Diagnostic Criteria

Late salivary cortisol levels of 290 and 275 strongly suggest Cushing's syndrome and require further diagnostic evaluation and appropriate management, according to the Endocrine Society 1
Values of 290 and 275 are significantly elevated and highly suggestive of Cushing's syndrome with loss of normal circadian rhythm of cortisol secretion, as reported by the Endocrine Society and the Lancet Diabetes and Endocrinology 2
These elevated values represent a failure of the normal nocturnal nadir in cortisol production, which is a hallmark of Cushing's syndrome, as stated by the Endocrine Society and the Lancet Diabetes and Endocrinology 1, 2

Confirm Cushing's syndrome diagnosis with additional tests, including 24-hour urinary free cortisol measurement and low-dose dexamethasone suppression test, as recommended by the Endocrine Society and the Lancet Diabetes and Endocrinology 1, 2
Determine ACTH dependency by measuring morning plasma ACTH levels, with ACTH >5 ng/L suggesting ACTH-dependent Cushing's syndrome, according to the Endocrine Society 1
Localize the source of Cushing's syndrome based on ACTH status, using pituitary MRI, CRH stimulation test, and bilateral inferior petrosal sinus sampling for ACTH-dependent disease, and adrenal CT or MRI scan for ACTH-independent disease, as recommended by the National Comprehensive Cancer Network and the Endocrine Society 3, 4

Treatment depends on the cause of Cushing's syndrome, with options including transsphenoidal surgery for Cushing's disease, laparoscopic adrenalectomy for adrenal adenoma, and open adrenalectomy with possible adjuvant therapy for adrenal carcinoma, as stated by the National Comprehensive Cancer Network and the Endocrine Society 3, 4
Medical therapy options are available when surgery is contraindicated or unsuccessful, including adrenal steroidogenesis inhibitors and pituitary-directed medications, as recommended by the National Comprehensive Cancer Network and the Lancet Diabetes and Endocrinology 2, 4

Untreated Cushing's syndrome leads to significant morbidity and mortality, with complications including cardiovascular disease, diabetes, osteoporosis, and immunologic disorders, as reported by the National Comprehensive Cancer Network 4
Specific symptoms to monitor include central obesity, proximal muscle weakness, wide purple striae, and hypertension, as stated by the Endocrine Society and the National Comprehensive Cancer Network 1, 4

False positive results can occur with severe obesity, alcoholism, depression, and disrupted sleep-wake cycles, as reported by the Lancet Diabetes and Endocrinology and the Endocrine Society 1, 2
In children and adolescents, Cushing's syndrome typically presents with weight gain combined with growth failure, which distinguishes it from simple obesity, as stated by the Endocrine Society 1
For patients with suspected cyclic Cushing's syndrome, periodic repeated testing may be necessary as cortisol levels can fluctuate between normal and elevated, as recommended by the Lancet Diabetes and Endocrinology 2

The Endocrine Society recommends measuring morning plasma ACTH to classify Cushing's syndrome as ACTH-dependent (>5 ng/L) or ACTH-independent (low or undetectable ACTH) 5
ACTH >29 ng/L has 70% sensitivity and 100% specificity for Cushing's disease (pituitary source) 5

Patients with Cushing's syndrome may exhibit skin changes, such as facial plethora, easy bruising, and wide purple striae, as well as body habitus changes like central obesity and dorsocervical fat pad enlargement, according to the National Comprehensive Cancer Network 6
Musculoskeletal symptoms, including proximal muscle weakness, and cardiovascular signs, such as hypertension, are also common in Cushing's syndrome 6
Metabolic signs, including evidence of hyperglycemia or diabetes, and other symptoms like hirsutism, psychiatric disturbances, and mood disorders, may be present in patients with Cushing's syndrome 6

Bilateral inferior petrosal sinus sampling (BIPSS) is the gold standard for differentiating pituitary from ectopic ACTH sources, with diagnostic criteria of central-to-peripheral ACTH ratio ≥2:1 before stimulation and ≥3:1 after CRH or desmopressin stimulation, as recommended by the Endocrine Society 5