Incidentalomas are common affecting 1% and 7% of 40 and 70 year olds respectively. By contrast endogenous Cushings syndrome is excessively rare. 10% of cases of Cushings syndrome are caused by an autonomous adrenal tumour where, having confirmed the diagnosis (symptoms and signs, cortisol excess, suppressed ACTH, suppressed contralateral adrenal) the treatment of choice is indeed adrenalectomy. Complexities arise around the suggestion that 1015% of all incidentalomas have subclinical Cushings Syndrome (SCCS), but diagnostic criteria are variable and confusing. Biochemical diagnosis has relied upon demonstrating abnormalities in a combination of tests (UFF, dexa suppression (DST), diurnal cortisol rhythm, late night salivary cortisol, ACTH and DHEA). Even when investigators have made a diagnosis of SCCS, results of adrenalectomy have been variable with reversal of hypercortisolism and resolution of clinical features in some studies but not all. The issue is one of diagnosing mild Cushings syndrome set against the certainty of normality when faced with diagnostic tests of variable sensitivity and specificity. Specifically for the 1mg DST the trade off between sensitivity and specificity is dependent upon the cortisol cut-off points used to define pass or fail. Thus a cortisol value of <1.8 ug/dl (50 nmol/l) effectively excludes Cushings syndrome - sensitivity is high at over 95%, but specificity is low at only 7080%, effectively meaning that 1 in every 4 or 5 patients who do not suppress to this level will be normal. Specificity can be increased to over 95% if the cut off is raised to a cortisol of 5 ug/dl (140 nmol/l), but with a compromise in sensitivity. Current guidelines suggest the use of more than one high sensitive screening test and where uncertainty remains, use the diagnostic dimension of time. Adrenalectomy for all incidentalomas who fail to suppress at whatever cut off following DST is quite simply bad practice. DONT DO IT!
Declaration of interest: There is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported.
Funding: No specific grant from any funding agency in the public, commercial or not-for-profit sector.