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A 29-year-old female presented with progressive swelling over the body, weight gain, menstrual irregularity. On examination, her BP was 160/100 mm Hg, pulse rate 86/min, weight 88 kg, height 155 cm. Buffalo hump was present with broad purplish striae over the abdomen. Proximal muscle weakness was present. Her investigations revealed Hb 12.6 g%, fasting blood sugar (FBS) 170 mg%, creatinine 0.9, Na 140 mEq/L, K 3.4 mEq/L (Fig. 2.1).
How would you approach a case of suspected Cushing’s syndrome?
Medicine
Step 1—rule out exogenous Cushing’s by history of drug (steroid) intake
Step 2—rule out pseudo-Cushing’s by clinical evaluation and screening tests
Step 3—perform diagnostic tests for confirming endogenous Cushing’s syndrome
Step 4—perform tests for finding out possible cause of Cushing’s
Step 5—radiological investigations for localizing tumor (Flowchart 2.1). Table 2.1 listed the various tests for screening. Two screening tests are recommended for confirming hypercortisolism taking into consideration their sensitivity and specificity, and also the availability.
Dexamethasone is used for suppression testing because, unlike prednisolone, it does not cross-react in radioimmunoassay for cortisol.
The interpretation of the results depends upon the assay used and the local laboratory calibration.
• These assays differ widely in their accuracy and the values near the cut-off value close to the functional limit of detection should be interpreted carefully as precision deteriorates at the lower levels.
• There are many drugs and conditions which can interfere with the measurement of cortisol and while interpreting, the physician should be aware of these limitations. Drugs like estrogen containing pills, increase cortisol binding globulin and thereby cause false positive results.
• Sensitivity and specificity of the various tests depend upon the cut-off value that was taken.
• In the case of any equivocal results, rescreening may be required.
As exogenous Cushing’s syndrome is more common than the endogenous one, exclusion of this condition is very important. In iatrogenic Cushing’s syndrome, cortisol levels are low unless the patient is taking a corticosteroid (such as prednisolone), which may cross-react in radioimmunoassay of cortisol. Apart from the history, basal 8:00 AM cortisol value will differentiate the exogenous from the endogenous Cushing’s syndrome. A suppressed cortisol value with Cushingoid features suggests exogenous cause except for cyclical Cushing’s syndrome which can have low values sometimes.
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