History A 50 y/o was referred for evaluation of azotemia. 10 yrs ago, he experienced sudden onset of pain on his right big toe. His serum uric acid was elevated. He was diagnosed to have gout and was prescribed medication but he was poorly compliant. The gouty attacks recurred lately hence, he decided to undergo thorough check- up. He denies dysuria, flank pain or hesitancy. He has nocturia. Physical Exam BP is 120/70 Obese numerous tophi in his metacarpo-phalangea l elbow joint no edema Salient Features A 50 y/o obese male diagnosed 10 years ago to have gout with gouty attacks recurring lately and was referred for evaluation of azotemia Patient experiences nocturia but there is no dysuria, flank pain or hesitancy, and edema BP is 120/70 Numerous tophi in his metacarpo-phalangeal elbow joint

Clinical Impression Gouty nephropathy – Patients with prolonged forms of hyperuricemia are predisposed to a more chronic tubulointerstitial disorder, often referred to as gouty nephropathy – Distinctive feature: presence of crystalline deposits of uric acid and monosodium urate salts in kidney parenchyma – Clinically, gouty nephropathy is an insidious cause of renal insufficiency. – Early in its course GFR may be near normal despite focal morphologic changes in medullary and cortical interstitium, proteinuria and diminished urinary concentrating ability

Algorithm/Sequence of Events Renal Deposition of Urates Pelvic Calculi Parenchymal Urate (microtophi) Tubular Uric Acid (obstruction) Gout Renal Insufficiency

Differential Diagnosis Diabetic Nephropathy – Kimmelstiel-Wilson syndrome – a progressive kidney disease caused by angiopathy of capillaries in the kidney glomeruli – characterized by nephrotic syndrome and diffuse glomerulosclerosis.

Spectrum of Disease Diagram Lower testing threshold Upper testing threshold Pretest probability Do nothing. Rule out the disease Treat the patient without waiting for more information Do additional diagnostic exams to confirm diagnosis (testing zone) 20 % 70% % 60%