Acquired distal renal tubular acidosis

Abstract

A 67-year-old black man was admitted to the West Side Veterans Administration Hospital in Chicago because of weakness and clinical signs of volume contraction. He gave no history of vomiting, diarrhea, diuretic use, or any other obvious cause of volume depletion. Physical examination revealed an afebrile thin man with decreased skin turgor. His blood pressure, 100/80 mm Hg in the supine position, fell to 90/70 mm Hg on standing. Ophthalmic examination revealed early cataracts. The remainder of the physical examination was unremarkable. The patient had a history of chronic congestive heart failure, sickle-cell trait, mild renal insufficiency, chronic normochromic normocytic anemia, and recurrent urinary tract infections. A plain chest x-ray film showed cardiomegaly. An electrocardiogram was consistent with an old myocardial infarction but was otherwise unremarkable. An intravenous pyelogram performed several months previously showed distortion of the calyceal system in the right kidney without evidence of hydronephrosis or papillary necrosis. On admission, the BUN was 76 mg/dl; it decreased to 33 mg/dl after 2 days of fluid replacement with normal saline. In response to this treatment, his plasma sodium and total protein levels also fell from 150 to 135 mEq/liter and from 7.9 to 6.0 g/dl, respectively. Plasma potassium, measured at 7.0 mEq/liter, fell to 4.8 mEq/liter after hydration and administration of sodium polystyrene sulfonate. After 2 weeks, the plasma potassium again rose to 7.0 mEq/liter, and a renal consultation was requested. At that time, the BUN was 56 mg/ dl; plasma creatinine, 2.5 mg/dl; plasma sodium, 140 mEq/liter; chloride, 112 mEq/liter; and total CO2, 17 mmol/liter; arterial blood pH was 7.32; PaCO2, 33 mm Hg; and Pa02, 82 mm Hg. Urine electrolytes were: sodium, 101 mEq/liter; potassium, 7 mEq/liter; and chloride, 66 mEq/ liter. Urinalysis showed 5 to 10 red blood cells per high-power field. A 24-hour urine collection contained no protein; the endogenous creatinine clearance was 35 mI/mm. After spontaneous voiding, the urine volume recovered by bladder catheterization was less than 20 ml. Following normal saline infusion for several days, plasma renin activity was 1.2 ng/ml/hr; plasma aldosterone, 0.9 ng/dl; and plasma potassium, 5.5 mEq/liter. After furosemide administration (40 mg orally at 6 P.M., 12 midnight, and 6 AM,), the plasma renin activity was 7.2 ng/ml/hr, plasma aldosterone was 3.8 ng/dl, and plasma potassium was 5.1 mEq/ liter. In the presence of spontaneous metabolic acidosis (venous blood pH, 7.28; PCO2, 43 mm Hg; and total C02, 19 mmol/liter), urine pH was 5.89. Ammonium excretion was 3.8 smol/min; titratable acid excretion, 8.5 mol/min; and net acid excretion, 12 jsmol/min. Intravenous administration of sodium sulfate had no effect on urine pH (from 5.92 to 5.93) or potassium excretion (from 43 to 42 mol/min), whereas sodium excretion increased from 25 to 110 smol/min. Administration of acetazolamide also had little effect on potassium excretion as shown by a subnormal increase in fractional potassium excretion (from 10% to 14.5%). Renal sodium handling was examined while the patient ingested a low-salt diet for 14 days. During this time, the patient was given 0.1 mg of fludrocortisone daily. On the 10th day of a diet containing 40 mEq of sodium and 60 mEq of potassium, sodium and potassium excretion exceeded and fell below intake by 52 and 19 mEq per 24 hours, respectively. After 4 additional days of a diet containing 10 mEq of sodium, the 24-hour sodium excretion fell to 23 mEq, a value still greater than the dietary intake. Plasma potassium ranged from 6.1 to 6.6 mEq/liter throughout the 14 days of observation. Dietary sodium restriction was terminated on the 14th day because the patient had lost 1.6 kg in weight and had developed a postural change in blood pressure and pulse.