Q J Med 2003; 96: 531-540
© 2003 Association of Physicians
Masterclasses in medicine |
An integrative physiological approach to polyuria and hyponatraemia: a ‘double-take’ on the diagnosis and therapy in a patient with schizophrenia
From the 1Department of Internal Medicine C, Rambam Medical Center, Faculty of Medicine, Technion Israel Institute of Technology, Haifa, Israel, 2Nephrology Unit and Department of Internal Medicine, University of Stellenbosch, Cape Town, South Africa, 3Division of Nephrology, University of Alberta Hospital, Edmonton, Canada, and 4Division of Nephrology, St. Michael’s Hospital, University of Toronto, Toronto, Canada
A patient with a history of schizophrenia was brought to the emergency department with extensive self-inflicted soft tissue injuries. Primary polydipsia was evident on admission, because he had a maximally dilute urine, a urine flow rate of 10 ml/min, and hyponatraemia (100 mmol/l). During an imaginary consultation with Professor McCance in which he applied basic principles of integrative physiology and a deductive analysis in quantitative terms, other reasons for the polyuric state were considered. Moreover, based on the very low value for the concentration of urea in plasma (< 0.7 mmol/l, BUN 1 mg /dl), the goals of therapy to prevent osmotic demyelination became evident. Applying this simple approach, a more comprehensive and accurate differential diagnosis, and a plan for therapy to avoid serious complications was compiled.
Address correspondence to Professor M.L. Halperin, Professor of Medicine, University of Toronto, St. Michael’s Hospital Annex, Lab #1, Research Wing, 38 Shuter Street, Toronto, Ontario, M5B 1A6, Canada. e-mail: mitchell.halperin{at}utoronto.ca