A Rare Entity in Cushing’s Disease: Severe Hypokalemia and Metabolic Alkalosis Seda Turgut 1 *, Muzaffer Ilhan 2 , Rabia Soytas 3 , Murat Alay 4 , Rumeyza Kazancioglu 4 1 Department of Endocrinology and Metabolism, University of Health Science Bakırköy Dr. Sadi Konuk Training and Research Hospital, Istanbul, TR 2 Department of Endocrinology and Metabolism, Bezmialem Vakif University, Istanbul, TR 3 Department of Internal Medicine, Bezmialem Vakif University, Istanbul, TR 4 Department of Nephrology, Bezmialem Vakif University, Istanbul, TR * Corresponding Author: Seda Turgut E-mail: seda.dr@gmail.com ABSTRACT Objective: This case report aimed to highlight the prominence of considering Cushing's disease (CD) in the differential diagnosis of severe hypokalemia and metabolic alkalosis. Case Report: A 63-year-old woman who was admitted to the emergency room with fatigue and severe weakness of extremities. Biochemistry results indicated severe hypokalemia (potassium = 1.2 mmol/L) and metabolic alkalosis (pH = 7.83) and based on further endocrinological investigations, the final diagnosis of CD was confirmed, and magnetic resonance imaging revealed a microadenoma in the right side of the pituitary gland. Transsphenoidal surgery was performed. After surgery, biochemical assessments showed normal potassium levels and corrected metabolic alkalosis without any further treatment. The hypothalamic–pituitary–adrenal axis recovered in nearly eight months and the patient was in remission. Conclusions: Although hypokalemia could be present in CD, none of the previous studies have reported hypokalemia as severe as in this case. This case report highlighted the prominence of considering CD in the differential diagnosis of severe hypokalemia and metabolic alkalosis that could be a crucial part of biochemical features in CD. Keywords: Cushing’s Disease, Hypokalemia, Metabolic Alkalosis Case Report Received 11-02-2020 Accepted 01-03-2021 Available Online: 28-03-2021 Published 30-032-2021 Distributed under Creative Commons CC-BY-NC 4.0 OPEN ACCESS INTRODUCTION Cushing’s syndrome (CS) is an endocrine disease characterized by chronic exposure to glucocorticoids and the most common reason for CS is therapeutic administration of exogenous glucocorticoids (1). ACTH-dependent CS (ADCS) is mostly caused by a pituitary corticotrope adenoma [Cushing’s disease (CD)] in approximately 80% of cases, and less frequently by an extra pituitary tumor (ectopic ACTH syndrome). In addition to that, CS may be ACTH independent (AICS) when it is caused by excess production of cortisol by unilateral adrenocortical tumors or by bilateral surrenal hyperplasia or dysplasia (2). CS can precipitate several biochemical alterations such as hypokalemia, metabolic alkalosis, and hypernatremia, this may be caused by mineralocorticoid effects of cortisol. However, these alterations caused nonspecific clinical findings and their role in CD is still matter of debate. Hypokalemia and metabolic alkalosis are found rarely in CD although it is present 57% in ectopic ACTH syndrome ( 3). Previous limited studies have suggested that many patients with AICS are associated with hypokalemia and metabolic alkalosis, there are a few numbers of cases reported with hypokalemia and metabolic alkalosis in CD (4-7). The patient presented here is an unusual case of CD in which severe hypokalemia and metabolic alkalosis were the presenting findings. CASE REPORT A 63-year-old woman was admitted to the emergency room with a two-week history of fatigue, severe weakness of the lower and upper extremities, mild hypertension, and confusion. MSD Medical Science and Discovery ISSN: 2148-6832