Long standing paraparesis: A rare presentation of distal renal tubular acidosis

Pankaj Kumar; Prabhjot Dhillon; Geetanjali Jindal; Shivani Randev; Vishal Guglani

doi:10.4103/amhs.amhs_121_20

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CASE REPORT

Year : 2021 | Volume : 9 | Issue : 1 | Page : 120-122

Long standing paraparesis: A rare presentation of distal renal tubular acidosis

Pankaj Kumar, Prabhjot Dhillon, Geetanjali Jindal, Shivani Randev, Vishal Guglani
Department of Pediatrics, GMCH, Chandigarh, India

Date of Submission	03-Jun-2020
Date of Decision	15-Oct-2020
Date of Acceptance	16-Oct-2020
Date of Web Publication	26-Jun-2021

Correspondence Address:
Dr. Pankaj Kumar
Department of Pediatrics, Government Medical College Hospital, Chandigarh
India

Source of Support: None, Conflict of Interest: None

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DOI: 10.4103/amhs.amhs_121_20

Abstract

Neurologic manifestations can accompany systemic diseases, and primary disease can be identified with a careful history, physical examination, and laboratory investigations. Renal tubular acidosis (RTA) is an important differential diagnosis in any child presenting with failure to thrive. Hypokalemic distal RTA, also known as classic RTA or type 1 RTA, may present, though not so frequently , with weakness consequent upon hypokalemic paralysis, compounded by rickets.

Keywords: Acidosis, failure to thrive, hypokalemia, renal

How to cite this article:
Kumar P, Dhillon P, Jindal G, Randev S, Guglani V. Long standing paraparesis: A rare presentation of distal renal tubular acidosis. Arch Med Health Sci 2021;9:120-2

How to cite this URL:
Kumar P, Dhillon P, Jindal G, Randev S, Guglani V. Long standing paraparesis: A rare presentation of distal renal tubular acidosis. Arch Med Health Sci [serial online] 2021 [cited 2021 Aug 1];9:120-2. Available from: https://www.amhsjournal.org/text.asp?2021/9/1/120/319375

Introduction

Renal tubular acidosis (RTA) is a group of transport defects secondary to reduced proximal tubular reabsorption of bicarbonate (HCO₃₋), the distal secretion of protons (hydrogen ion, H⁺), or both, resulting in impaired capacity for net acid excretion and persistent hyperchloremic metabolic acidosis. In hypokalemic distal RTA, also known as classic RTA or type 1 RTA, the deficiency is secondary to either a secretory (rate) defect or a gradient (permeability) defect. However, symptoms related to hypokalemia including weakness and paralysis are uncommon.^[1] We report a case who presented for evaluation of paraparesis, and on workup, she was found to have distal RTA with hypokalemia and rickets and responded dramatically to treatment. Early recognition and adequate treatment is the key to successful outcome.

Case Report

A 6-year-old girl after having a normal vaginal birth delivery with an uneventful antenatal period presented with complaints of not growing well since birth and weakness of bilateral lower limbs for 4 years of age. Weakness started following some febrile illness requiring admission with mild pain and reluctance to bear weight and gradually progressed over the next 2 months to an extent that she was not able to stand, even with support. Developmental milestones were normal in other sectors. Family history was not contributory. Examination revealed weight (8 kg) and length (80 cm), well below 3^rd centile, pallor, features suggestive of rickets, and an old malunited fracture in the right forearm. Central nervous system examination was normal apart from weakness in bilateral lower limbs with a power of 3/8, normally elicited Deep tendon reflexes (DTRs), and downgoing planters. Initial possibilities kept were of some metabolic myopathy or muscular dystrophy, but a review of history in detail revealed the presence of polyurea and polydipsia, which gave hint toward some renal tubular disorder. Investigations revealed normal anion gap metabolic acidosis with hypokalemia, with a positive urinary anion gap, so RTA was considered. Urine pH of 6.5 and FEHCO₃ <5 after correcting acidosis with sodium bicarbonate and a corresponding serum bicarbonate of 22.3 confirmed the type of RTA to be distal, type 1. Diagnosis of distal RTA was further supported by the presence of hypercalciuria and nephrocalcinosis and biochemical and radiological evidence of rickets [Table 1] and [Figure 1]. However, a diligent workup for the types RTA including genetic analysis was not possible due to financial constraints. The child also had hypophosphatemia, workup for which revealed normal parathyroid hormone and decreased TmP/glomerular filtration rate or Bijovet Index^[2] when calculated as per the normogram.^[3] There was no sensorineural hearing loss. She was started on alkali therapy in the form of sodium bicarbonate tablets, potassium and phosphate supplements, low sodium diet, and liberal fluid intake, to which she responded dramatically in the next 4 months to an extent of running unsupported, along with normalization of metabolic acidosis, hypokalemia, and hypophosphatemia.

Table 1: Investigations

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Figure 1: X-ray wrist showing fraying and splaying of lower end of the metaphysic of radius and ulna

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Discussion

RTA is a clinical syndrome that causes hyperchloremic metabolic acidosis due to a disorder of urine acidification. The acidification of urine in the distal tubule primarily depends on acid–base exchange transporters in intercalated cells. There are three related processes: provision of H⁺ and HCO₃⁻⁻ ions from H₂O and CO₂ by cytosolic carbonic anhydrase II (CA II), excretion of H⁺ ions into the collecting tubule by vacuolar H⁺-ATPase, and excretion of HCO₃⁻⁻ ions into the blood by the HCO₃⁻⁻/Cl⁻⁻ anion exchanger (AE1).^[4] Impaired function of any of these components can cause a defect in urine acidification, and the severity of functional defect depends on the importance of the affected component.^[5] Based on the pathophysiology, RTA has been classified into three types: type 1 (distal) RTA; type 2 (proximal) RTA; and type 4 RTA secondary to true or apparent hypoaldosteronism.^[1] These disorders can be either secondary to other causes or primary, with or without known genetic defects. The presence of alkaline urine during metabolic acidosis suggests defective renal acidification, as in distal RTA.^[6]

Clinical features in distal RTA include impairment of growth, polyuria, polydipsia, nephrocalcinosis, nephrolithiasis, and symptoms due to hypokalemia.^[1]

In children, distal RTA is almost always observed as a primary entity. Rarely, it occurs as a complication of systemic lupus erythematosus or Sjogren's syndrome. A proportion of cases with sporadic or autosomal recessive distal RTA show sensorineural deafness, which may be present from birth or manifest in late childhood. Metabolic myopathy, paralysis, and metabolic bone disease are common in adults and children with dRTA.^[7],[8]

Any child presenting with failure to thrive should have a venous blood gas done. If this shows a nonanion gap type of metabolic acidosis, then the next step is to determine urinary anion gap; if it is positive, the cause is RTA; if negative, then it is due to some gastrointestinal losses. RTA is further classified on the basis of urine pH and fractional excretion of bicarbonates into type 1 and type 2. Type 1 (distal) RTA has urine pH more than 5.5 and fractional excretion of bicarbonate less than 5, whereas in type 2 (proximal) RTA, urine pH is <5.5 and fractional excretion of bicarbonate more than 15. Treatment of distal RTA consists of correction of hypokalemia by potassium supplements, followed by correction of acidosis by alkali administration (sodium bicarbonate 7.5% [1 mEq/ml OR tablet 1000 mg = 12 mEq]; Shohl solution [1 mEq/ml]; and polycitra solution [2 mEq/ml]). The utility of sodium bicarbonate replacement in conditions associated with loss of sodium bicarbonate is well established. The initial dose is 2–3 mEq/kg/day which can be increased until blood bicarbonate level becomes normal. The amount of bicarbonate required to maintain acid base balance might be as high as 5–10 mEq/kg/day, and alkali therapy is usually lifelong. Hypophosphatemia if present needs phosphate supplementation 30–50 mg/kg/day. If hypercalciuria persists despite the correction of acidosis, administeration of thiazides may be necessary.

Conclusion

RTA should always be kept as a differential diagnosis in children with failure to thrive, especially if associated with neurological motor manifestations or rickets refractory to usual treatment.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.

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