Epidemiology and follow-up of Cushing's disease.

Little is known on the epidemiology of Cushing's disease (CD) as relevant data on such a rare disease can only be obtained from large-scale studies. We addressed this topic analyzing the data obtained in the Italian multicenter study which comprised nearly 300 patients with CD. The number of newly diagnosed patients with CD increased markedly in the second decade of the study (from 7.4 +/- 0.71 pts/year prior to 1987 to 26.4 +/- 4.12 after 1987) probably reflecting the heightened awareness of the disease and the increased availability of diagnostic tools. Urinary free cortisol (UFC) levels were significantly higher in men than in women and were inversely correlated with the time interval between appearance of symptoms and diagnosis. Recognition of CD among patients presenting with common diseases such as obesity, diabetes and hypertension requires highly sensitive screening tests (e.g. UFC, midnight cortisol in saliva, overnight dexamethasone suppression test) which however may yield false positive results. In doubt, second line testing using dex-CRH or desmopressin may distinguish between CD and pseudo Cushing. The different prevalence of CD and ectopic ACTH secretion (ES) undermines the diagnostic accuracy of tests used for the differential diagnosis of ACTH-dependent Cushing's syndrome (i.e. CRH, high dose dexamethasone, IPSS). Tests aimed at identifying ES rather than CD are needed to overcome this bias. Transsphenoidal surgery was the preferred choice of treatment for patients with CD, resulting in remission in 70% operated patients with a 15% relapse rate over 10 years follow-up. Definition of remission after surgery and parametres predictive of relapse, however, vary according to studies and long-term follow-up is required to establish their validity. Most clinical manifestations of hypercortisolism disappeared after remission although some long-lasting effects on the cardiovascular system had been observed. Finally, according to recent reports, mortality rates for patients cured of CD appear comparable to those of the general population.