Proximal renal tubular acidosis in children

Introduction of proximal renal tubular acidosis in children Proximal renal tubular acidosis (pRTA) is a proximal tubule that causes proximal tubule carbonation due to various secondary factors (drugs, toxicant damage, cystine storage disease, Wilson's disease) and/or congenital causes. Anhydrogenase dysfunction and H+ excretion disorder, HCO3-reduced absorption in the proximal tubules, and hyperchloremia metabolic acidosis and alkaline urine, can also cause hypokalemia. basic knowledge The proportion of illness: 0.003% Susceptible people: children Mode of infection: non-infectious Complications: metabolic acidosis hypokalemia

Causes of proximal renal tubular acidosis in children

(1) Causes of the disease

1. Primary: The cause is unknown, generally considered to be related to heredity, only manifested as HCO3-reabsorption disorder, without other renal tubular and glomerular dysfunction.

(1) Sporadic babies are temporary.

(2) Hereditary is persistent, showing autosomal dominant or autosomal recessive inheritance.

2. Secondary: often secondary to systemic disease, can be associated with a variety of renal tubular dysfunction, Fanconi (Fanconi) syndrome is the most common.

(1) with other genetic diseases: hereditary diseases with other proximal tubular dysfunction: such as idiopathic Fanconi syndrome, cystine disease, ocular-brain-renal syndrome (Lowe syndrome), Hereditary fructose intolerance, tyrosinemia, galactosemia, glycogen accumulation disease, mitochondrial myopathy, metachromatic leukodystrophy, etc.

(2) Drug and toxin kidney damage: such as carbonic anhydrase inhibitor, expired tetracycline, methyl 3-chromone, maleic acid poisoning, heavy metal (calcium, lead, copper, mercury) poisoning.

(3) Others: such as subacute necrotizing encephalomyelopathy (Leigh syndrome), tetralogy of Fallot, intestinal malabsorption, hyperparathyroidism, renal cyst disease, hereditary nephritis, chronic rejection of renal transplantation, multiple Sexual myeloma, Sjögren syndrome, amyloidosis, chronic active hepatitis, recurrent renal calculi, renal medullary cystic disease, Wilson's disease, etc.

(two) pathogenesis

Under normal conditions, glomerular filtration of HCO3-99% is reabsorbed, with proximal tubules reabsorbing 80% to 90%, the remaining 2% in the medullary ridge, and 8% in the distal tubule reabsorption, while HCO3- Reabsorption is closely related to the function of H+ secretion by tubular cells. In the small tube, H+-Na+ is exchanged, Na+ is reabsorbed into the cell and combined with HCO3- to form NaHCO3, and then enters the blood, which reserves the alkali reserve for the body, relying on Na+-K+ -ATPase, the proximal tubule reabsorbs most of the sodium in the glomerular filtrate, Cl- and water are passively reabsorbed with Na+, in addition, the proximal tubule actively reabsorbs all K+, 2/3 calcium and part of the phosphate, pRTA For the proximal renal tubular reabsorption of HCO3-deficiency, HCO-renal threshold decreased, normal human 25 ~ 26mmol / L, infants 22mmol / L, and pRTA 18 ~ 20mmol / L, when the patient's plasma HCO3- concentration is normal, That is, more than 15% of HCO3- is discharged into the urine (only 1% of normal people). Even in mild acidosis, if the patient's plasma HCO3- concentration is still higher than the renal threshold, HCO3- is still discharged into the urine. Only severe acidosis can cause the patient to discharge acidic urine. As the proximal renal tubules reduce HCO3-reabsorption, the Na+-H+ exchange is reduced, Na+ Loss from the urine, causing low sodium, dehydration, loss of Na+ leads to increased aldosterone, Na+, Cl- retention, and due to increased loss of HCO3-, in order to maintain anion balance, while retaining C1-, high chloride blood Symptoms, under the action of aldosterone, Na+-K+ exchange and retain Na+, can cause hypokalemia, long-term metabolic acidosis may cause growth and development disorders by blocking the secretion or response of growth hormone, leading to proximal tubular reabsorption The cause of HCO3-disorders is unclear, probably due to the immature development of renal tubular function. In secondary causes, most of them are caused by endogenous metabolites or foreign substances that damage the proximal tubule epithelium.

Prevention of proximal renal tubular acidosis in children

Primary pRTA is not known for its etiology, and there is no reliable preventive method; pRTA prevention secondary to systemic diseases is mainly for those secondary to drug and toxin kidney damage and other diseases such as intestinal malabsorption and hyperthyroidism. Active prevention and control.

Complications of proximal renal tubular acidosis in children Complications, metabolic acidosis, hypokalemia

Can be complicated by nutritional disorders, metabolic acidosis, hypokalemia, rickets, growth retardation and so on.

Symptoms of proximal renal tubular acidosis in children Common symptoms Hypokalemia fatigue, nausea, metabolic acidosis, inability, renal glucosuria, kidney stones, hyponatremia

1. Primary pRTA: mainly found in male infants, with other proximal renal tubular reabsorption defects such as diabetes, phosphorus, etc., spontaneously disappear in 1 to 2 years old.

2. Metabolic acidosis and low sodium, hypokalemia: may have growth retardation, nausea, vomiting and other acidic poisoning and weakness, fatigue, muscle weakness, constipation and other hyponatremia and hypokalemia, due to HCO3 - The renal threshold is reduced to 15-18 mmol/L at pRTA, and acidic urine (pH < 5.5) can be discharged below 15 mmol/L. Severe acidosis is rare.

3. Others: Because there is no serious acidosis, such as without the proximal tubule phosphorus absorption disorder, no hyperphosphatemia, rare metabolic bone disease, renal calcification, kidney stones.

4. Secondary pRTA: In addition to the above symptoms, there are primary symptoms, and it is easily covered by the symptoms of the primary disease. Some patients relieve themselves with age, and should be alert to secondary pRTA.

Examination of proximal renal tubular acidosis in children

The blood biochemical examination of pRTA has plasma HCO3- and pH lowering, hyperchloremia, sodium or potassium normal or decreased, urine pH can be alkaline or acidic according to blood HCO3-level, 24h urine HCO3-only titratable acid normal, urinary calcium Can be increased or normal, routine imaging studies, such as ECG and B-ultrasound.

Diagnosis and diagnosis of proximal renal tubular acidosis in children

diagnosis

When patients have high chloride acidosis and normal anion gap, especially with hypokalemia, renal glucosuria, high amino aciduria, hyperphosphatemia with hypophosphatemia and hyperuricuria, Consider pRTA, such as severe metabolic acidosis, plasma HCO3-<1518mmol/L, morning urine pH5.5, NH+4 displacement>40mol/(min·1.73m2), and exclude HCO3 from gastrointestinal tract loss -, can diagnose the disease, if there is a certain acidosis, but the urine pH is not low, should be done with ammonium chloride load test to exclude dRTA, sodium bicarbonate reabsorption test is helpful to confirm the diagnosis, the methods are:

1. Oral method: oral sodium bicarbonate 2 ~ 10mmol / (kg · d), increase the dose every 3 days until acidosis correction, determination of plasma and urine HCO3- and creatinine content, calculated by the following formula: urine HCO3- Excretion rate = (urine HCO3-x plasma creatinine) / (plasma HCO3-x urine creatinine) × 100% Normal human is 0, such as >15% can diagnose pRTA; <5% is dRTA; 5% to 10% is type III RTA The HCO3-renal threshold can also be measured, and the HCO3-renal threshold is lowered in this disease.

2. Intravenous method: intravenous infusion of 5% sodium bicarbonate 2.5ml / (kg · h), when the blood HCO3- returns to normal or above normal level is stable, 1 hour per hour, and in the middle of the urine , check HCO3- and creatinine, calculate the urine HC03-excretion rate according to the above formula.

Differential diagnosis

Hyperchloremia-induced metabolic acidosis is the main clinical manifestation of this disease. Many clinical diseases can cause dehydration and acidosis, such as diarrhea, ketoacidosis, etc. When it is difficult to correct dehydration and acidosis, it should be Be wary of this disease, check accordingly, growth retardation in young children may be the most important or even the only manifestation of this disease, so children with developmental delay should pay close attention to the presence or absence of pRTA, application of bicarbonate or bismuth. The amount of acid buffer must be 6mmol / (kg · d) to maintain plasma CO2 binding capacity of 22mmol / L, which can be distinguished from distal RTA, urine concentration dysfunction is lighter than distal RTA.

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