| Abstract|| |
We report a rare case of two young male siblings with sickle cell anemia who presented with bilateral lower limb deformities, failure to thrive, polyuria, and polydipsia. On investigations, they were found to have normal anion gap metabolic acidosis, hypokalemia, and nephrocalcinosis were seen on ultrasonography of the kidneys. These reports were suggestive of distal renal tubular acidosis (dRTA). They were started on oral alkali replacement and potassium therapy with which clinical improvement was seen. Conventionally, renal tubular dysfunction is thought to occur infrequently in patients with sickle cell anemia. Hence, we report this rare association between sickle cell anemia and dRTA.
|How to cite this article:|
Bharani A, Manchanda R, Singh RK, Prashant S. Distal renal tubular acidosis in sickle cell anemia. Saudi J Kidney Dis Transpl 2018;29:1000-4
|How to cite this URL:|
Bharani A, Manchanda R, Singh RK, Prashant S. Distal renal tubular acidosis in sickle cell anemia. Saudi J Kidney Dis Transpl [serial online] 2018 [cited 2019 Nov 21];29:1000-4. Available from: http://www.sjkdt.org/text.asp?2018/29/4/1000/239637
| Introduction|| |
Sickle cell disease (SCD) is a multisystem disorder. Sickle cell nephropathy is a well-known entity and may comprise hyposthenuria, urinary acidification defects, and glomerular dysfunction., Renal tubular dysfunction should be considered in the evaluation of all children presenting with failure to thrive, polyuria, bony deformities, refractory rickets, hypokalemia, and metabolic acidosis. The exact prevalence of acid-base disorders in patients with SCD is unknown and presumably low. The largest study done reported metabolic acidosis in 42% of cases of SCD. We report a rare case of distal renal tubular acidosis (dRTA) in two male siblings with sickle cell anemia presenting with failure to thrive, polyuria, polydipsia, and bony deformities.
| Case Report|| |
A 10-year-old male child presented to us with a complaint of gradually progressive deformities in both lower limbs since the age of three years. He also had a history of polydipsia, polyuria, and failure to gain weight and height since the same age. There was a history of admission for jaundice at four years of age; the evaluation showed hemolytic anemia which required one blood transfusion. There was a history of fracture of the femur shaft at the age of seven years. The index case was third of the four siblings born out of a non-consanguineous marriage. The eldest sibling was a 13-year-old asymptomatic female; the second sibling was a female child who succumbed to diarrheal illness at one year of age and his 2-year-old younger male brother is also similarly affected with bilateral lower limb deformities, failure to thrive, polyuria, and polydipsia [Figure 1]. On examination, index case had a height of 97 cm (for expected of 136.5 cm; 71%) and weight of 15 kg (for expected of 28 kg; 53%), with a reversed upper segment to lower segment ratio. On examination, he had pallor, icterus and enlarged spleen 2 cm below the costal margin, signs of rickets in the form of frontal bossing, wrist widening, and genu valgus at the right knee and genu varum at the left knee (windswept deformity) [Figure 1] and [Figure 2]. Investigations done in the index case and siblings are summarized in [Table 1]. The investigations were done in both of them showed normal anion gap metabolic acidosis on arterial blood gas analysis. Serum electrolytes showed hypokalemia with hyperchloremia. Urine examination showed elevated calcium/creatinine ratio suggestive of hypercalciuria and urinary pH was acidic (pH: 6) despite metabolic acidosis; and other investigations were normal as shown in [Table 1]. Hemoglobin electrophoresis revealed sickle cell anemia. Ultrasonography of the abdomen showed medullary nephrocalcinosis in the index case and renal calculi in the sibling [Figure 3]. Reports were confirmatory of dRTA with sickle cell anemia. Both the children were started on oral sodium bicarbonate and oral potassium supplements along with folic acid supplements with which they showed considerable improvement in their symptoms.
|Figure 1: Clinical Photograph showing genu valgus at the right knee and genu varum at the left knee in lower limbs of index case (left) and younger sibling (right).|
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|Figure 2: (a) X-ray anteroposterior view of lower limbs (index case) showing genu valgus at right knee and genu varum at left knee; (b) X-ray lateral view of lower limbs (index case) showing osteopenia and anterior bowing.|
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|Figure 3: Ultrasonography image showing nephrocalcinosis in the index case.|
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| Discussion|| |
Although reliable epidemiological data are not available with a population of 1.25 billion individuals, India is estimated to be home to over 50% of the global SCD patient population. The sickle cell gene is mainly concentrated in scheduled tribal, scheduled caste, and other backward caste populations of Madhya Pradesh, Orissa, Chhattisgarh, Jharkhand, Gujarat, Andhra Pradesh, and Kerala states of India where carrier frequencies range between 5% and 40% or more. Common complications include acute painful episodes, stroke, dactylitis, leg ulceration, pulmonary hypertension, acute chest syndrome, priapism, and nephropathy.
Many renal structural and functional abnormalities have been associated with SCD. The rate of oxygen consumption by the kidney is very high, and it is especially sensitive to the vaso-occlusion-induced hypoxia that can result from red cell sickling. Sickled RBCs cause hypoxia and microinfarctions of the vasa recta that supply the distal tubules, impairing their function, and resulting in acidification defects. Acidification defect is also thought to be related to the inability to maintain the hydrogen ion gradient. Sickle cell nephropathy encompasses a large spectrum of renal abnormalities such as hyposthenuria, defects of urinary acidification and potassium excretion, glomerular abnormalities, hematuria, papillary necrosis, and at times, renal medullary carcinoma. If not adequately controlled, it may even progress to end-stage renal disease. Conventionally, metabolic acidosis and hyperkalemia were thought to occur infrequently. However, recent studies have shown that the metabolic acidosis in SCD may be underestimated and could be related to impaired ammonium availability possibly due to an altered corticopapillary gradient. This report describes the finding of hypokalemic hyperchloremic metabolic acidosis in patient with sickle cell anemia.
Renal tubular acidosis (RTA) and diarrhea are important causes of normal anion gap metabolic acidosis in children. Considering the spectrum of tubular functions, disorders involving the tubules result in varied manifestations emphasizing the need for their consideration in many clinical conditions. Nonspecific features such as failure to thrive, polyuria, and polydipsia mandate the need for high index of suspicion for these disorders. Workup to rule out secondary causes of RTA (e.g., obstructive uropathy, reflux nephropathy, and chronic tubulointerstitial nephritis) should also be done. Patients with distal RTA are known to have normocalcemia with hypercalciuria. Calcium excretion may also be determined on spot urine samples; ratio of calcium to creatinine >0.2 mg/mg beyond infancy is significant.
The management of RTA includes the correction of metabolic acidosis with bicarbonate supplements [sodium bicarbonate 7.5% (1 mEq/Ml); Shohl solution (1 mEq/mL); and Polycitra solution (2 mEq/mL)]. Bicarbonate requirement is more in patients with proximal RTA (5-6 mEq/kg/day) compared to distal RTA (1-2 mEq/kg/day). Alkali therapy is usually combined with potassium replacement to avoid severe hypokalemia. Potassium supplements in patients with acidosis are usually administered as citrate salts. Long-term potassium replacement is however not required in patients with distal RTA.
Although bony pains, dactylitis and osteomyelitis, are far more common in the clinical course of sickle cell anemia, the presence of bony deformities along with metabolic acidosis should hint at presence renal tubular dysfunction and sickle cell nephropathy in such patients.
Conflict of Interest: None declared.
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Dr. Anjali Bharani
Department of Pediatrics, Index Medical College, Hospital and Research Center, Indore, Madhya Pradesh
[Figure 1], [Figure 2], [Figure 3]