Distal renal tubular acidosis and amelogenesis imperfecta: A rare association
A 10-year-old female, resident of Tamil Nadu born of second degree consanguineous marriage was admitted with inability to move all 4 limbs since early morning. The weakness had evolved over a period of 20 days initially presenting as calf muscle pain, progressing to difficulty in getting up from bed, and eventually involving all four limbs.\nThere was no prior history of fever, loose stools, vomiting, trauma or drug intake. No significant past medical history could be elicited except for polyuria and polydipsia for last 1 month. Antenatal, perinatal, and development history was unremarkable. There was no family history of periodic paralysis, cardiac, thyroid, renal or auto immune disorders. On examination, child had flaccid areflexic quadriparesis with power 2/5 in all limbs and no muscle wasting. Her higher mental functions, cranial nerves, sensory system and autonomic system examination were normal. Systemic examination was unremarkable. Her vitals were within normal range. Serum level of potassium was 1.5 meq/l and electrocardiogram showed prolonged QT interval, ST depression, T wave flattening in V1-V4, and the presence of ‘U’ waves. Child was given potassium replacement therapy and recovered from paralysis.\nShe had severe growth retardation with a weight of 15 kg and height of 110 cm (both below 5th centile). Intraoral examination revealed poor oral hygiene; the dentition was consistent with the chronological age. Enamel was hypoplastic with brownish orange discoloration and irregular mottling of occlusal surface of molar teeth. Based on the history, clinical and radiographic presentation provisional diagnosis of AI, hypoplastic type was made []. Routine lab investigations including renal and liver function tests were within normal range. Serum electrolytes showed hypocalcemia (7.2 mg/dl), hypophosphatemia (2.8 mg/dl) with normal serum magnesium and sodium. Her arterial blood gas revealed normal anion gap metabolic acidosis with respiratory alkalosis []. Thyroid and lipid profile were normal. Urine culture and sensitivity showed no growth and urine metabolic screening were negative. There was no glycosuria or proteinuria. The urinary potassium level was 24 meq/l, which indicates renal potassium wasting (exceeding 20 meq/l).\nIn view of persisting metabolic acidosis with normal anion gap, hypokalemia, and polyuria (2.5 l/m2/24 h) a possibility of distal RTA was considered, which was confirmed by necessary investigations. Three consecutive early morning urine pH was 7.5 and the urine pH after frusemide challenge was 7.5. Urine anion gap was positive and urinary calcium/creatinine ratio was 2. 24 h urinary calcium was 280 mg (increased), fractional excretion of bicarbonate was 4.5% and urine blood pCO2 difference was 4 mmHg (decreased). The ultrasound scan of the abdomen revealed bilateral renomegaly with increased cortical echoes. There was no evidence of nephrocalcinosis. Skeletal survey did not show any evidence of rickets. She was investigated for secondary causes of RTA and all investigations including her antinuclear antibody and auto immune profile were negative.\nThe child was managed symptomatically with potassium replacement therapy initially intravenously followed by oral supplementation with correction of acidosis and electrolyte abnormalities during the ICU stay and upon the diagnosis of distal RTA was started on long- term oral potassium citrate supplementation. The patient is currently under follow-up and her weakness and polyuria have improved dramatically.