A 37-year-old Hispanic man presented to the emergency department with three days of progressive dyspnea and fatigue. He had history of kidney disease since he was very young, including hypokalemia, nephrolithiasis and osteomalacia. His medications included potassium citrate, which he neglected to take for the past week.
He has four siblings, one of whom has a similar condition. Physical examination reveals a thin male in moderate respiratory distress. His BP was 128/72 mm Hg and his respiratory rate was 28 per minute. Lungs were clear and there was mild right-sided flank pain on palpation. A chest radiograph showed no acute cardiopulmonary disease. A computed tomography urogram was performed (see image).
Labs show a potassium level of 2.7 mEq/L, chloride level of 128 mEq/L, sodium level of 141 mmol/L, bicarbonate level of 8 mEq/L, and a creatinine level of 1.5 mg/dL. Toxicology screening is negative. Arterial blood gas reveals a pH of 7.25 and a pCO2 of 11. Urinalysis shows a pH of 7, small blood, and 40 white cells.
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This patient had a diagnosis of type 1 renal tubular acidosis as evidenced by severe hyperchloremic non-anion gap metabolic acidosis with hypokalemia. His urine pH was over 5.5 and previous urine studies had demonstrated hypercalciuria. He received intravenous fluids, including sodium bicarbonate, and potassium was repleted. He felt much better within 24 hours. He was counseled on the importance of compliance to his potassium citrate supplements.
Type 1 RTA is known to be associated with a number of autoimmune diseases such as Sjogrens and rheumatoid arthritis. Certain drugs such as ifosfamide and amphotericin can also cause type 1 RTA. Less commonly, type 1 RTA can be an inheritable disorder.
Autosomal dominant and autosomal recessive variants have been described with abnormalities localized to proteins in the alpha-intercalated cells on the collecting tubules. Specifically, mutations in the chloride-bicarbonate exchanger and the H+ ATPase of the alpha intercalated cells have been implicated in some familial cases.
Patients with inheritable type 1 RTA, in addition to hypokalemic, hyperchloremic metabolic acidosis, generally have hypercalciuria with nephrocalcinosis very early in life. Some families may also have associated sensorineural hearing loss.
Answer: Alpha-intercalated cells of the collecting tubules
This clinical case was prepared by Kevin T. Harley, MD, Assistant Clinical Professor of Medicine, and Oliver Ross, MD, resident in internal medicine, at the University of California, Irvine.
- Karet, F. Inherited distal renal tubular acidosis. J Am Soc Nephrol 2002;13:2178-2184.