A weight-related intravenous dexamethasone suppression test distinguishes obese controls from patients with Cushing's syndrome

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Abstract
To establish a rapid test for Cushing''s syndrome we measured serum cortisol during and following iv dexamethasone infusions (5 .mu.g .cntdot. kg-1 .cntdot. h-1 for 5 h from 10.00 h) in simple obesity (N = 19) and in Cushing''s syndrome (N = 12). We had first established that 5 .mu.g .cntdot. kg-1 .cntdot. h-1 was the lowest dose which consistently lowered serum cortisol in simple obesity. In obesity, serum cortisols ranged from undetectable (<30) to 48 nmol/l at 17.00, <30 to 37 at 19.00 and < 30 to 38 at 08.00 h the following day. Serum cortisol at these three times did not show any overlap between simple obesity and Cushing''s syndrome. Having established these findings we proceeded to study a group of patients with polycystic ovarian disease. These patients behaved differently. Their values at 17.00 and 19.00 h did not overlap those of Cushing''s syndrome. However, at 08.00 h, 5 of the 7 had values within the range seen in Cushing''s syndrome with a mean of 290 .+-. 99 nmol/l. In conclusion, 17.00 and 19.00 h serum cortisol levels distinguish between Cushing''s syndrome and both simple obesity and polycystic ovarian disease. However, in the latter, cortisol suppression is less prolonged than in simple obesity. This finding may be important for our understanding of the pathogenesis of the disease.