Cushing’s syndrome (CS) prevalence is variable in type 2 diabetes (T2DM). Subclinical CS is associated with increased morbidity and mortality.1 We aimed to identify the prevalence of undiagnosed CS in an unselected population of patients with T2DM; and evaluate the utility of the late night salivary cortisol (LNSC) in screening.
Outpatients with T2DM from St Vincent’s public and private hospitals were recruited to undergo a LNSC test and an overnight 1mg dexamethasone suppression test (DST). If either test was positive, patients proceeded to a 24-hour urine free cortisol (UFC); if two tests were positive, a 48-hour low dose dexamethasone test (LDDST) was recommended.
242 patients were recruited over 36 months, of which 107 completed LNSC and DST. Thirty-three (30.8%) patients tested positive on either or both tests: 13 (12%) were positive on both, 10 (9.3%) were positive on ODT only and 10 (9.3%) were positive on LNSC only. Concordance between ODT and LNSC was 81%. UFC was measured in 21/33 patients and positive in 1 patient who had negative repeat testing. Of 13 patients with two positive tests, three proceeded to the LDDST, which were negative in all cases. No clinical diagnoses of CS were made by treating clinicians following positive screening results. Patients with positive results (ODT and/or LNSC) were older (mean age 71.1±2.1 vs 59.3±1.4 years, p<0.0005), had longer duration of diabetes (14±1.5 vs 10±0.95 years,p<0.05) and poorer renal function (mean eGFR 64±3.7 vs 82±1.6, p<0.0005).
Screening an unselected T2DM population did not yield any cases of CS, but it revealed considerable cortisol dysregulation evidenced by abnormal DST or LNSC. Whether this reflects subclinical CS or influences morbidity and mortality remains uncertain. Further, the validity of these screening tools is not well established in older patients or those with renal impairment.