Endocrine Abstracts

A 47-year-old female presented with facial swelling, easy bruising, and concern regarding possible Cushing’s syndrome. She had developed secondary amenorrhoea 3 years previously; biochemistry suggested hypogonadotrophic hypogonadism, felt to be hypothalamic secondary to low BMI and intense exercise. She was normotensive, and BMI was 17.4. There was no evidence of abdominal striae, proximal myopathy or hirsutism, but her face appeared rounder and plethoric compared with a previous photograph. Investigations revealed significantly elevated urinary free cortisol (UFC) excretion at 441 and 564 nmol/24hr (normal<162). However, urine volumes were 4.3 and 6.7 litres respectively, indicative of polyuria, a lesser-known cause of false positive UFC. Early morning cortisol was 610 nmol/l following an overnight dexamethasone suppression test (DST), and 513 nmol/l following a 48-hour low-dose DST. ACTH was 27 ng/l. Contrast-enhanced pituitary MRI showed a 3 mm pituitary fossa lesion consistent with a microadenoma. However, subsequent investigations ultimately suggested a diagnosis of pseudo-Cushing’s. Firstly, salivary cortisol measurement demonstrated intact diurnal rhythm, with appropriately low late-night concentrations. Secondly, due to the degree of non-suppression of cortisol post-dexamethasone, serum dexamethasone was quantified by liquid chromatography-mass spectrometry following a repeat ODST. Dexamethasone concentration was 1.7 nmol/l, with values >3 nmol/l considered necessary to suppress cortisol. Finally, a dynamic contrast-enhanced pituitary MRI suggested the previously identified pituitary mass most likely represented a Rathke’s cleft cyst. Furthermore, from a clinical perspective her facial swelling, plethora, and easy bruising all resolved after she was encouraged to drink to thirst only. An association between pseudo-Cushing’s and false positive UFC and ODST is well established. However, where results of these investigations are significantly elevated, and above levels expected with pseudo-Cushing’s, additional factors should be considered such as the impact of high fluid intake and serum dexamethasone concentration, as exemplified within this case.