Diagnosis and treatment of renal tubular disorders in children

Type 3 renal tubular acidosis associated with growth hormone deficiency

BACKGROUND

We identified two boys with type 3 renal tubular acidosis (RTA) and growth hormone deficiency and we sought to differentiate them from children with classic type 1 distal RTA.

METHODS

We reviewed all children <6 years of age with RTA referred over a 13-year period and compared the growth response to alkali therapy in these two boys and in 28 children with only type 1 distal RTA.

RESULTS

All children with type 1 RTA reached the 5th percentile or higher on CDC growth charts within 2 years of alkali therapy. Their mean height standard deviation score (SDS) improved from -1.4 to -0.6 SDS and their mean mid-parental height (MPH) SDS improved from -0.6 to 0 SDS after 2 years. In contrast, the boys with growth hormone deficiency had a height SDS of -1.4 and -2.4 SDS after 2 years of alkali and the MPH SDS were both -2.6 SDS after 2 years of alkali therapy. Growth hormone therapy accelerated their growth to normal levels and led to long-term correction of RTA.

CONCLUSIONS

A child with type 1 RTA whose height response after 2 years of alkali therapy is inadequate should undergo provocative growth hormone testing.

Anaesthetic implications of cystinosis

The author presents and discusses the anaesthetic care of a 12-yr-old boy with cystinosis. Cystinosis is a recessively inherited disorder of amino acid metabolism resulting in the abnormal intracellular accumulation of cystine. Anaesthetic care may be affected by variable end-organ involvement, most notably progressive renal deterioration beginning with the development of Fanconi syndrome and progressing to overt renal failure during the first decade of life. Additional organ system involvement may lead to cirrhosis with portal hypertension, diabetes mellitus, and hypothyroidism. Identification of the extent of end-organ involvement during the preoperative evaluation will help in the provision of safe anaesthetic care for such patients.

Primary distal tubular acidosis in childhood: clinical study and long-term follow-up of 28 patients

The long-term follow-up of 28 patients with congenital primary tubular acidosis is described. Ten patients had affected siblings but no history of similar symptoms in the preceding generation. Deafness was associated in 14 patients and developed before 12 years of age. Deafness was present in all familial cases, and patients without deafness showed no familial incidence, suggesting the existence of two different entities. All patients had growth retardation, which was more severe in the older patients and was always markedly improved by alkaline therapy. Rickets was found in some patients but seemed related to vitamin D deficiency. Catch-up growth was limited to the first 2 years of therapy in patients treated before 2 years of age, but sometimes lasted longer in older patients. Of the 12 patients who reached adulthood, those without rickets achieved a normal height but the others did not. We believe that therapy should be continued throughout life because of the risk of nephrocalcinosis.

Distal renal tubular acidosis as the initial manifestation of systemic lupus erythematosus in an adolescent

Distal renal tubular acidosis (dRTA) as the initial manifestation of systemic lupus erythematosus (SLE) has not been described previously. We report a 14-year-old female adolescent, first presenting with findings consistent with dRTA, whose renal biopsy demonstrated immune mesangial deposits consistent with lupus nephritis. Seven months later, she developed classic extrarenal manifestations of SLE. We recommend that adolescents with dRTA be evaluated and followed closely for the possibility of SLE.

Hypocitraturic and hypercalciuric renal tubular acidosis with nephrocalcinosis in a 4-year-old boy

A 4-year-old boy suffering from hypocitraturic and hypercalciuric renal tubular acidosis with nephrolithiasis and nephrocalcinosis is reported. Renal function tests indicated that the patient had type 1 renal tubular acidosis. Potassium citrate rather than potassium bicarbonate, sodium citrate or bicarbonate is the preferred treatment for stones in RTA-I.

Type 4 renal tubular acidosis (sub-type 2) associated with idiopathic interstitial nephritis

An 18-month-old girl presenting with anorexia and failure to thrive, was referred for adenoidectomy. Arterial hypertension was discovered on physical examination. Laboratory results revealed hyperkalaemic, hyperchloraemic, metabolic acidosis, with slight azotemia. Urinary aldosterone excretion and plasma renin were decreased. Renal biopsy showed idiopathic interstitial nephritis. The diagnosis of type 4 renal tubular acidosis, sub-type 2, i.e. primary hyporeninaemic secondary hypoaldosteronism was proposed. According to our knowledge, this disease has not previously been reported in young children, but is well known in azotaemic adults. We therefore propose the inclusion of this uncommon renal disease in the differential diagnosis of failure to thrive in childhood.

Alterations of urinary carbon dioxide tension, electrolyte handling and low molecular weight protein excretion in acute pyelonephritis

Renal tubular function tests were performed in 45 children suffering from upper and lower urinary tract infections. Determinations were made of the urinary carbon dioxide tension in maximally alkaline urine as an index of distal tubular H+-ion secretion, of urinary protein excretion, and of urinary sodium and phosphate handling. Urinary PCO2 was low (2.7 +/- 13.9 mmHg) in acute pyelonephritis compared to values in healthy children (52 +/- 32 mmHg) or those with cystitis (48 +/- 34 mmHg). At the onset of pyelonephritis an elevated fractional excretion of sodium (1.38 +/- 0.38 vs. 0.50 +/- 0.20%) and decreased phosphate reabsorption (69.2 +/- 7.1 vs. 90.4 +/- 4.9%) were also observed. Significantly elevated urinary low molecular weight protein excretion was also found in pyelonephritis. These data indicate the existence of proximal and distal tubular dysfunction at the onset of acute bacterial pyelonephritis.

Renal tubular acidosis type 4 in neonatal unilateral kidney diseases

Three neonates, two with unilateral renal vein thrombosis and one with unilateral dysplastic kidney, developed type 4 renal tubular acidosis, manifested by nonazotemic hyperkalemic metabolic acidosis with alkaline urine pH and reduced potassium excretion. Normal plasma concentrations of sodium, aldosterone, and renin activity, together with normal renal fractional excretion of sodium, supported the diagnosis of renal tubular acidosis type 4, subtype 5. Arginine HCl loading studies showed that despite their ability to bring the urine pH to less than 5.8, net acid excretion was inadequate relative to the corresponding plasma bicarbonate concentration. Treatment with oral bicarbonate resulted in sustained normalization of blood acid-base status and accelerated linear growth in the first two infants, in whom spontaneous recovery occurred by ages 8 and 15 months, respectively. At that time, the affected kidneys were extremely small with distorted collecting systems; the contralateral kidneys showed compensatory hypertrophy. In the third infant, persistent acidosis and growth failure resulted from medical noncompliance; the removal of the dysplastic kidney at 7 months of age was followed by the return to normal blood acid-base status and normalized tubular hydrogen and potassium excretion. We conclude that neonatal unilateral kidney disease can result in renal tubular subtype 5. Spontaneous recovery can be expected, presumably because of " autonephrectomy " of the affected kidney plus the compensatory hypertrophy of the contralateral kidney.