Decoding the Renal Puzzle: Idiopathic Distal Renal Tubular Acidosis in a 23-Year-Old Woman with Nephrocalcinosis and Metabolic Acidosis

Introduction: Distal Renal Tubular Acidosis (dRTA) is a cause of normal anion gap metabolic acidosis. Its etiology encompasses various factors, including autoimmune diseases, genetic mutations affecting chloride-bicarbonate exchanger genes, and drug-induced occurrences, such as with lithium, amphotericin B and Toluene inhalation due to glue sniffing. dRTA can also manifest as an idiopathic disorder. Case Description: A 23-year-old female with an unremarkable medical history presented to the emergency department with nausea, vomiting, bilateral flank pain and fever. Prior to seeking emergency care, the patient had visited an urgent care facility where she was provisionally diagnosed with a urinary tract infection and treated with Bactrim. Upon admission, her creatinine level was 1.14 mg/dL, serum potassium was 2.9 mmol/L), serum bicarbonate 10 mmol/L, and an anion gap of 12. Urine pH was 6.0. CT abdomen/pelvis disclosed severe bilateral nephrocalcinosis in the renal pyramids and the presence of calculi. Urine anion gap was positive. Subsequent investigations ruled out rheumatoid arthritis, Sjogren's disease, lupus and multiple myeloma. Patient was discharged on PO sodium bicarbonate and potassium chloride which was switched as an outpatient to potassium citrate. 24 hour urine collection recommended as an outpatient prior to starting potassium citrate to evaluate for hypocitraturia could not be done due to financial constraints. Discussion: Distal RTA is an uncommon disorder. Pathophysiology of distal RTA involves damage to alpha-intercalated cells in the distal tubule, impairing the secretion on hydrogen ions, consequently raising the urine pH and causing metabolic acidosis. Hypokalemia occurs due to the failure of H/K ATPase. This case highlights the importance of checking a urine anion gap in patients with normal anion gap metabolic acidosis and the need to consider distal RTA in patients who have nephrocalcinosis. Timely diagnosis of distal RTA is crucial to preventing long-term complications such as nephrocalcinosis and nephrolithiasis, allowing early initiation of alkali and potassium supplementation. Furthermore, distal RTA can sometimes be the first manifestation of an underlying autoimmune condition and once it is diagnosed, attempts should be made to identify the cause of the distal RTA.