Cushing’s syndrome is considered to be a rare disorder that results from prolonged exposure to glucocorticoids. However, there are few epidemiological studies to provide adequate data to describe the incidence and prevalence of the condition accurately. Most cases are diagnosed between the ages of 20 and 50, although any individual may be affected at any age.
The presentation of the symptoms of Cushing’s syndrome can vary greatly. In addition, many of the symptoms overlap with those caused by other health conditions, such as metabolic syndrome and polycystic ovary syndrome. This can make the diagnosis of the condition difficult. It is also difficult to establish epidemiological trends in Cushing’s syndrome, because not all cases of the disease are diagnosed. However, it is important that diagnosis is made as soon as possible, because early diagnosis and treatment of the condition are associated with improved morbidity and mortality rates.
There are several population-based studies that have reported the incidence and mortality rates of Cushing’s syndrome in certain populations over a discrete period of time.
A study in Denmark followed 166 patients with Cushing’s syndrome for 11 years, finding an incidence of 2 cases per million population per year. Of the 166 patients, 139 had benign disease. There was a mortality rate of 16.5% in the follow-up period of 8 years, with most deaths occurring in the year after the initial diagnosis, often before the initiation of treatment. The causes of death of patients with Cushing’s syndrome in the study included severe infections, cardiac rupture, stroke and suicide.
A study in Spain found 49 cases of Cushing’s syndrome over a period of 18 years, with an incidence of 2.4 cases per million inhabitants per year and a prevalence of 39.1 cases per million. The standard mortality ratio in this study was 3.8, in addition to an increase in morbidity rates.
A low incidence of endogenous Cushing’s syndrome was established by the population-based studies outlined above, corresponding to approximately 2 cases per million. Some studies have an estimated incidence as low as 0.7 people per million.
However, the incidence of subclinical Cushing’s syndrome may be underestimated in certain population groups, such as those with osteoporosis, uncontrolled diabetes mellitus or hypertension. For example, of 90 obese patients with uncontrolled diabetes mellitus in one study, three had Cushing’s syndrome. This yielded a prevalence of 3.3%, which is considerably higher than the incidence reported in the population-based studies. However, these findings should be supported by larger studies.
Females are more likely to be affected by Cushing’s syndrome than males, with a risk ratio of approximately 3:1. There does not appear to be a genetic link that involves an ethnic susceptibility to the condition.
Surgery is the first-line treatment option for most cases of overt disease and remission is achieved in the majority of patients, approximately 65-85%. However, for up to 1 in 5 patients the condition recurs, and the risk does not appear to level off, even after 20 years of follow-up.
The risk of mortality for individuals with Cushing’s syndrome is estimated to be 2-3 times higher than that of the general population, based on epidemiological studies.