Endocrine Abstracts

When investigating patients for possible Cushing’s, repeat testing should be considered despite initial negative results if there is a high index of suspicion. We report a case of a patient whose initial tests for Cushing’s yielded conflicting results; cyclical Cushing’s Disease was diagnosed following persistent testing. A 40 year-old lady (BMI 38.0 kg/m²) was seen in the obesity clinic with a 12-month history of weight gain. She had clinical features of Cushing’s including dorso-cervical fat pad, plethoric facial appearance, striae, easy bruising and proximal myopathy. There were no visual field defects. Because the results from an initial low dose dexamethasone suppression test (LDDST) were lost by the laboratory, the LDDST was repeated; this suppressed (cortisol<28 nmol/l). Subsequently, the initial LDDST result was found by the laboratory; this did not suppress (cortisol=114 nmol/l). Repeated 24-hour urinary free cortisols (UFCs) at weekly intervals demonstrated three peaks and two troughs in UFC concentrations [480, <30, 415, 149, 617 (NR 0–165 nmol/24 hr)]. Midnight cortisol concentrations were raised (359 & 311 nmol/l). ACTH concentrations were 71 nmol/l (0–46 ng/l). Her CRH test showed a marked rise in ACTH (>50%) and cortisol (>20%). High dose dexamethasone suppression test was consistent with pituitary Cushing’s (cortisol=181 nmol/l). MRI revealed a 5 mm pituitary microadenoma. FT4, prolactin, gonadotrophin and serum potassium concentrations were normal. Our patient underwent transphenoidal adenectomy; histology confirmed a corticotroph adenoma. In the presence of Declaration of interesting results for Cushing’s with a suspicious clinical picture, diagnostic suspicion remained high. Further investigation demonstrated 3 peaks (above normal range) and 2 troughs (within normal range) of cortisol secretion. In cases of suspected Cushing’s with normal or discrepant biochemical findings, measurements of cortisol secretion should be repeated at intervals to demonstrate 3 peaks and 2 troughs. A combined dexamethasone-CRH test should also be considered. The importance of perseverance when investigating possible Cushing’s is exemplified by this case.

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.