A Child with Distal (Type 1) Renal Tubular Acidosis Presenting with Progressive Gross Motor Developmental Regression, Medullary Nephrocalcinosis, and Acute Renal Failure - A Case Report

Abstract

Background: Distal renal tubular acidosis (dRTA) is a condition characterized by the impaired ability to secrete hydrogen ions from the distal tubule. In pediatric patients, common clinical features of dRTA include excessive urine production (polyuria), frequent nighttime urination (nocturia), poor growth and weight gain (failure to thrive), difficulty with bowel movements (constipation), abnormal breathing, and the presence of kidney stones (nephrolithiasis). While urinary tract infections (UTIs) are frequently associated with dRTA, renal failure is uncommon and seldom reported in children. Case Presentation: A 10-year-old girl was referred for the evaluation due to a progressive loss of gross motor milestones over a period of 3 years. She also experienced an acute episode of paralysis and was found to have bilateral medullary nephrocalcinosis (right staghorn calculus) accompanied by moderate renal failure and a UTI. Her development in other areas was appropriate for her age. Importantly, there was a history suggestive of excessive urine production (polyuria), increased thirst (polydipsia), and frequent nighttime urination (nocturia). Physical examination revealed proximal myopathy, characterized by a waddling gait and a positive Gower’s sign, as well as diminished reflexes and muscle tone in the lower limbs. Laboratory tests indicated the presence of sepsis (total leukocyte count – 26,660, CRP-174.29) and elevated renal parameters (serum creatinine – 4.27) along with active urinary abnormalities. Urine culture and sensitivity testing showed significant growth of Escherichia coli (>100,000 CFU). A computed tomography scan of the kidneys, ureters, and bladder revealed a staghorn calculus on the right side, as well as bilateral medullary nephrocalcinosis and swollen kidneys. The patient was diagnosed with dRTA based on several factors, including hypokalemic hyperchloremic metabolic acidosis with a normal anion gap, high urine pH, borderline hypercalciuria, presence of medullary nephrocalcinosis, and after ruling out other potential differential diagnoses. Following treatment for the UTI and sepsis, as well as standard treatment for dRTA, the child exhibited symptomatic improvement. Her creatinine levels returned to 0.8 mg/dL, and the septic markers declined to normal levels. To further investigate the cause of the initial decline in renal function in addition to the UTI, a renal biopsy was performed. Conclusion: This case report emphasizes the significance of including medullary nephrocalcinosis and renal tubular acidosis in the list of potential diagnoses for patients presenting with progressive gross motor developmental regression, acute flaccid paralysis, and proximal myopathy. Timely identification of these conditions can help avoid unnecessary and expensive investigations, while also facilitating prompt clinical recovery in affected children. Early diagnosis plays a crucial role in guiding appropriate management strategies and improving patient outcomes.