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 Table of Contents  
CASE REPORT
Year : 2021  |  Volume : 9  |  Issue : 1  |  Page : 120-122

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


Department of Pediatrics, GMCH, Chandigarh, India

Date of Submission03-Jun-2020
Date of Decision15-Oct-2020
Date of Acceptance16-Oct-2020
Date of Web Publication26-Jun-2021

Correspondence Address:
Dr. Pankaj Kumar
Department of Pediatrics, Government Medical College Hospital, Chandigarh
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/amhs.amhs_121_20

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  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 Sep 18];9:120-2. Available from: https://www.amhsjournal.org/text.asp?2021/9/1/120/319375




  Introduction Top


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 Top


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 3rd 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 Top


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 Top


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.



 
  References Top

1.
Bagga A, Sinha A. Evaluation of renal tubular acidosis. Indian J Pediatr 2007;74:679-86.  Back to cited text no. 1
    
2.
Drueke TB, Lacour B. Disorders of calcium, phosphate and magnesium metabolism. In: Johnson RJ, Feehally J, editors. Comprehensive Clinical Nephrology. London: Harcourt Publishers; 2000. p. 1-11.  Back to cited text no. 2
    
3.
Walton RJ, Bijvoet OL. Nomogram for the derivation of renal tubular threshold concentration. Lancet 1975;2:309-10.  Back to cited text no. 3
    
4.
Rodriguez SJ. Renal tubular acidosis: The clinical entity. J Am Soc Nephrol 2002;13:2160-70.  Back to cited text no. 4
    
5.
Batlle D, Haque SK. Genetic causes and mechanisms of distal renal tubular acidosis. Nephrol Dial Transplant 2012;27:3691-704.  Back to cited text no. 5
    
6.
Herrin TJ. Renal tubular acidosis. In: Avner ED, Harmon WE, Niaudet P, editors. Pediatric Nephrology. 5th ed. Baltimore: Lippincot Williams and Wilkins; 2004. p. 757-76.  Back to cited text no. 6
    
7.
Jha R, Muthukrishnan J, Shiradhonkar S, Patro K, Harikumar K, Modi KD. Clinical profile of distal renal tubular acidosis. Saudi J Kidney Dis Transpl 2011;22:261-7.  Back to cited text no. 7
[PUBMED]  [Full text]  
8.
Zhang C, Ren H, Shen P, Xu Y, Zhang W, Wang W, et al. Clinical evaluation of chinese patients with primary renal tubular acidosis. Intern Med 2015;54:725-30.  Back to cited text no. 8
    


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