Endocrine Abstracts

Section 1: Case history: This 41 year old lady was seen in the Endocrine clinic with an 8 year history of worsening hypertension, obesity and Type 2 diabetes. She had no conditions known to cause physiological hypercortisolism, no exogenous steroid use and had clear physical features of Cushing’s syndrome.

Section 2: Investigations: Investigations confirmed Cushing’s syndrome with two elevated urinary free cortisol assessments (UFC) (934 and 906 nmol/24hr) and failure of cortisol suppression after 1mg overnight dexamethasone suppression (221 nmol/l). An ACTH of 39.1 ng/l confirmed this was ACTH dependent and secondary hypothyroidism (TSH 1.68 mIU/l, free T4 8.2pmol/l) suggested a pituitary origin. The rest of the pituitary panel was normal.MRI pituitary showed no lesion. A CRH test was indeterminate with basal to peak increases of >50% for ACTH (24.1 to 86.5 ng/l) but <20% for cortisol (783 to 806 nmol/l). She was therefore referred to the regional pituitary MDT who recommended contrast pituitary MRI and Inferior Petrosal Sinus Sampling (IPSS).

Section 3: Results and treatment: She was commenced on dose titrated metyrapone and prophylactic low molecular weight heparin to reduce her thrombotic risk. The contrast MRI pituitary showed a small non-enhancing area on the right side which might represent a microadenoma. IPSS assessment (off metyrapone with UFC confirmation of elevated cortisol) however was more suggestive of an ectopic than pituitary origin. The central to peripheral ACTH ratio of <2 prior to corticotrophin releasing hormone (CRH) and <3 post CRH didn’t support a pituitary source. A prolactin-normalised central to peripheral ACTH ratio of 0.4, was also suggestive of ectopic ACTH syndrome rather than Cushing’s disease.

Section 4: Conclusions and points for discussion: Localisation of ACTH-secreting adenomas is commonly challenging due to their small size. It is however essential to increase the likelihood of successful surgical remission from Cushing’s syndrome. This patient has gone on to have a full body contrast CT scan and spoiled gradient echo MRI of the pituitary gland. The latter has recently been described as superior for detecting small microadenomas over contrast MRI. Normalising the central to peripheral ACTH ratio with prolactin also helps to reduce the false negative rate of the procedure. We describe the use of these novel techniques and their benefit in clinical practice in cases where adenoma detection is challenging.