8411 Ectopic ACTH-dependent Cyclical Cushing’s Syndrome- the Art of Hide-and-seek

Abstract Disclosure: H. Mon: None. A. Kapoor: None. S. Qureshi: None. M. Martineau: None. K. Meeran: None. Case report: A 72-years-old lady was admitted with hypokalaemia, hyperglycaemia with metabolic alkalosis with background hypertension, type2 diabetes, osteoporosis and right-sided breast cancer treated with chemotherapy and radiotherapy 3years ago. She was previously seen in Endocrinology Clinic for similar episode and deemed not having Cushing’s or Conn’s syndrome on workup. During this admission, although there was no obvious Cushingoid appearance, there was refractory hypokalaemia. On further exploration, there were previous admissions with similar episodes in UK and in her home country, within the same year, a few months apart. Therefore, endocrinology workup was conducted for suspected cyclical Cushing’s syndrome. It demonstrated raised 24-hour urinary free cortisol of 5643 nmol/24hour (reference range 0-164 nmol/24hours), unsuppressed low dose dexamethasone suppression test with cortisol level of 800 nmol/L and increased ACTH level of 429 ng/L. MRI (pituitary) showed no pituitary lesion with probable empty sella and CSF filled. However, CT (thorax) showed enlarging lesion (previously from 1cm to 1.6cm) in the left lower lobe, concerning lung metastasis or primary lung malignancy. PET scan showed left lower lobe nodule having low-grade activity with likelihood of indolent malignancy and appearances of physiologic adrenal hyperplasia. Management: Given persistently high cortisol levels during admission with ongoing hyperglycaemia and refractory hypokalaemia, metyrapone was started and titrated accordingly. Her clinical condition including potassium and cortisol levels effectively responded to metyrapone. Gallium scan was booked for detail localization with ongoing lung MDT (multidisciplinary team meeting) and neuroendocrine tumour MDT.However, after starting metyrapone, she had type 1 respiratory failure, not responding to initial antibiotics. After excluding other possible respiratory aetiologies, empirical treatment for Pneumocystosis pneumonia (PCP) was initiated, after which blood test for Beta-D-glucan was found out to be significantly raised, supporting the presumptive diagnosis. Conclusion: Our case highlighted the following interesting points 1. diagnostic challenges, due to the fluctuating nature of cyclical Cushing’s syndrome, presenting with recurrent hypokalaemia. 2. the interesting nature of likely ACTH-dependent cyclical Cushing’s syndrome, progressing into florid Cushing’s syndrome, with efficacy to metyrapone 3. rare and compelling combination of 3 conditions of Cyclical Cushing’s syndrome, being ectopic ACTH-dependent and complicated by Pneumocystosis pneumonia (PCP). Presentation: 6/1/2024