Table of Contents

Cushing's syndrome diagnosis

Due to high morbidity and mortality of untreated hypercortisolism, a prompt diagnosis is essential.

Cushing's syndrome is usually easy to diagnose clinically owing to its characteristic features.

Laboratory tests

8 A.M. cortisol is the best test for hypocortisolism (e.g. to look for pituitary insufficiency); 24-hour urine free cortisol is the best test for hypercortisolism

Morning and midnight serum cortisol levels

24h urine free cortisol excretion

11 PM salivary cortisol: this is the time of the usual cortisol nadir. Test must be run at NIH approved lab. Accuracy is as good as low-dose Dexamethasone suppression test

Serum cortisol levels after low (1 mg) and high (8 mg) dexamethasone

The dexamethasone suppression test (DST) is used to assess adrenal gland function by measuring how cortisol levels change in response to an injection of dexamethasone. It is typically used to diagnose Cushing's syndrome.

Plasma ACTH and serum cortisol levels after Desmopressin stimulation test 1).

Magnetic resonance imaging (MRI)

Anatomical localization of source of excess ACTH Cushing's disease can be quite challenging. Sometimes, it becomes very difficult to differentiate ectopic ACTH source from Cushing's disease 2) 3).

Subsequent to the diagnosis of ACTH-dependent Cushing's syndrome, the next step involves anatomical localization of the source of the ACTH secretion. Various biochemical and radiological techniques have been established to help in localization of the neoplastic lesion. Radiological techniques including computed tomography (CT)/magnetic resonance imaging (MRI) have poor sensitivity (around 60%) 4).

Salivary cortisol test

see Salivary cortisol test

References

1)
Leal-Cerro A, Martín-Rodríguez JF, Ibáñez-Costa A, Madrazo-Atutxa A, Venegas-Moreno E, León-Justel A, García-Hernández N, Luque RM, Castaño JP, Cano DA, Soto-Moreno A. Desmopressin test in the diagnosis and follow-up of cyclical Cushing's disease. Endocrinol Nutr. 2014 Feb;61(2):69-76. doi: 10.1016/j.endonu.2013.04.017. Epub 2013 Oct 30. English, Spanish. PubMed PMID: 24183946.
2)
Ezzat S, Asa SL, Couldwell WT, Barr CE, Dodge WE, Vance ML, et al. The prevalence of pituitary neuroendocrine tumors: A systematic review. Cancer. 2004;101:613–9.
3)
Utz A, Biller BM. The role of bilateral inferior petrosal sinus sampling in the diagnosis of Cushing's syndrome. Arq Bras Endocrinol Metabol. 2007;51:1329–38.
4)
Aron DC, Raff H, Findling JW. Effectiveness versus efficacy: The limited value in clinical practice of high dose dexamethasone suppression testing in the differential diagnosis of adrenocorticotropin-dependent Cushing's syndrome. J Clin Endocrinol Metab. 1997;82:1780–5.