Screening of Cushing's syndrome in adult patients with newly diagnosed diabetes mellitus

Approach to the patient with possible Cushing's syndrome

Clinical decision making for patients with suspect hypercortisolism involves a complex diagnostic assessment. Cushing's syndrome remains one of the most challenging endocrine pathologies. Most clinical features overlap with those of common diseases found in the general population, and some patients have an atypical clinical presentation with only isolated symptoms. Recently, several studies have suggested that the prevalence of Cushing's syndrome is higher than previously thought. Therefore, efficient screening tests are needed to identify the few uncovered patients also among unselected high-risk ambulatory patients with disorders potentially related to cortisol excess. The recommended diagnostic tests are 24-h urinary free cortisol, 1-mg overnight dexamethasone suppression test, and late-night salivary cortisol. Once the diagnosis of Cushing's syndrome is established, the next step is the measurement of plasma ACTH. Then, dynamic test and appropriate imaging procedures are the most useful noninvasive investigations for the differential diagnosis. Patients with Cushing's disease are generally responsive to the CRH test and to high-dose glucocorticoid feedback. Bilateral inferior petrosal sinus sampling is considered the gold standard for establishing the origin of ACTH secretion, and it is recommended in patients with ACTH-dependent Cushing's syndrome whose clinical, biochemical, or radiological studies are discordant or equivocal. The present clinical case shows that even if rare, the ectopic ACTH secretion should be considered also in those cases where the pretest probability is low. The management of Cushing's syndrome depends on the exact knowledge of its various causes, paying attention to the many potential diagnostic pitfalls. The choice of test, the modality of specimen collection (blood, urine, and saliva), the quality of measurement (assay methodology and standardization), and close dialogue among endocrinologists, chemical pathologists, and neuroradiologists are key factors for optimal care of patients.

The diagnosis of Cushing's syndrome: an Endocrine Society Clinical Practice Guideline

OBJECTIVE

The objective of the study was to develop clinical practice guidelines for the diagnosis of Cushing's syndrome.

PARTICIPANTS

The Task Force included a chair, selected by the Clinical Guidelines Subcommittee (CGS) of The Endocrine Society, five additional experts, a methodologist, and a medical writer. The Task Force received no corporate funding or remuneration.

CONSENSUS PROCESS

Consensus was guided by systematic reviews of evidence and discussions. The guidelines were reviewed and approved sequentially by The Endocrine Society's CGS and Clinical Affairs Core Committee, members responding to a web posting, and The Endocrine Society Council. At each stage the Task Force incorporated needed changes in response to written comments.

CONCLUSIONS

After excluding exogenous glucocorticoid use, we recommend testing for Cushing's syndrome in patients with multiple and progressive features compatible with the syndrome, particularly those with a high discriminatory value, and patients with adrenal incidentaloma. We recommend initial use of one test with high diagnostic accuracy (urine cortisol, late night salivary cortisol, 1 mg overnight or 2 mg 48-h dexamethasone suppression test). We recommend that patients with an abnormal result see an endocrinologist and undergo a second test, either one of the above or, in some cases, a serum midnight cortisol or dexamethasone-CRH test. Patients with concordant abnormal results should undergo testing for the cause of Cushing's syndrome. Patients with concordant normal results should not undergo further evaluation. We recommend additional testing in patients with discordant results, normal responses suspected of cyclic hypercortisolism, or initially normal responses who accumulate additional features over time.

Accuracy of diagnostic tests for Cushing's syndrome: a systematic review and metaanalyses

CONTEXT

The diagnosis of Cushing's syndrome (CS) requires the use of tests of unregulated hypercortisolism that have unclear accuracy.

OBJECTIVE

Our objective was to summarize evidence on the accuracy of common tests for diagnosing CS.

DATA SOURCES

We searched electronic databases (MEDLINE, EMBASE, Web of Science, Scopus, and citation search for key articles) from 1975 through September 2007 and sought additional references from experts.

STUDY SELECTION

Eligible studies reported on the accuracy of urinary free cortisol (UFC), dexamethasone suppression test (DST), and midnight cortisol assays vs. reference standard in patients suspected of CS.

DATA EXTRACTION

Reviewers working in duplicate and independently extracted study characteristics and quality and data to estimate the likelihood ratio (LR) and the 95% confidence interval (CI) for each result.

DATA SYNTHESIS

We found 27 eligible studies, with a high prevalence [794 (9.2%) of 8631 patients had CS] and severity of CS. The tests had similar accuracy: UFC (n = 14 studies; LR+ 10.6, CI 5.5-20.5; LR- 0.16, CI 0.08-0.33), salivary midnight cortisol (n = 4; LR+ 8.8, CI 3.5-21.8; LR- 0.07, CI 0-1.2), and the 1-mg overnight DST (n = 14; LR+ 16.4, CI 9.3-28.8; LR- 0.06, CI 0.03-0.14). Combined testing strategies (e.g. a positive result in both UFC and 1-mg overnight DST) had similar diagnostic accuracy (n = 3; LR+ 15.4, CI 0.7-358; LR- 0.11, CI 0.007-1.57).

CONCLUSIONS

Commonly used tests to diagnose CS appear highly accurate in referral practices with samples enriched with patients with CS. Their performance in usual clinical practice remains unclear.