Chapter 17:RENAL DISORDERS

Student Authors: Gauta Kgomo, Ismatou Balde and Neo Mahlatsi

Specialist Advisor: Dr Ashton Coetzee

Cover Image

This chapter covers the following topics:

RENAL ANATOMY AND PHYSIOLOGY

The kidneys are paired organs located between the T12 and L3 vertebrae. They are both retroperitoneal with the left kidney situated more superiorly than the right.

Gross Anatomy of the Kidney

The functional unit of the kidney is the nephron. The nephron is comprised of:

The functions of the kidney are to maintain homeostasis, which includes:

Pathology

Renal pathology can either be primary or secondary. Primary disease refers to an intrinsic structural or functional kidney abnormality that is symptomatic e.g. minimal change nephrotic syndrome, polycystic kidney disease, renal tumour. Secondary disease refers to a systemic condition that affects the kidney function e.g. HPT, post-infectious glomerulonephritis, Wegener’s granulomatosis, use of nephrotoxic drugs.

URINARY TRACT INFECTIONS (UTIs)

UTIs are quite common in children and occur more in females (30% of girls) than in boys (1%), except in the <1 year age group. They range from lower urinary tract disease (e.g. urethritis, cystitis) to more severe and complicated upper UTIs (e.g. pyelonephritis, renal abscesses). The UTI may be uncomplicated (lower UTI in a generally well child) or complicated (upper UTI or a systemically unwell child).

Aetiology

Urine is normally sterile but there is sometimes colonisation of urine and proliferation of disease-causing organisms. 90% of the bacteria which cause UTI form normal flora of the GIT. Common causative organisms include:

Risk Factors

Children at greater risk of developing a UTI are:

Clinical Features

They include:

Investigations

The following investigations should be done:

Management

It includes:

For the child with an uncomplicated UTI:

For the child with a complicated UTI:

NEPHRITIC SYNDROME

It is caused by glomerular damage and is characterised by a triad of symptoms – macro-/microscopic haematuria, oligo-/anuric renal failure and HPT.

Pathophysiology and Aetiology

Nephritic syndrome is caused by damage to the glomerulus of any cause:

Nephritic syndrome is most commonly due to post-streptococcal glomerulonephritis i.e. there is a group A streptococcus throat infection 5-21 days prior to the nephritis (more common than after impetigo). Glomerular damage is due to deposition of circulating immune complexes or as a result of bacterial protein deposition within the basement membrane, leading to in-situ immune activation.

Clinical Features

The child may present with:

Complications

Nephritic syndrome may be complicated by:

Investigations

They should include:

Management

One must:

Table 17.1: Approach to Coloured Urine

Approach to Coloured Urine

Urine may be coloured because of:

  • Haematuria:
    • Patients with glomerular haematuria will have positive dipsticks and abnormal RBCs or RBC casts on urinalysis. Causes include:
      • Post strep GN
      • IgA nephropathy
      • Infections
      • Toxins
      • Trauma
    • Patients with non-glomerular haematuria will have positive dipsticks and normal RBC on urinalysis. Causes include:
      • Urolithiasis
      • Pyelonephritis
      • Obstruction
      • Cystitis
      • Menstruation
      • Strenuous exercise
      • Tumours
      • Iatrogenic
  • Haemoglobinuria; causes include:
    • DIC
    • Intravascular haemolysis (e.g. sickle cell)
  • Myoglobinuria; causes include:
    • Rhabdomyolysis
    • Trauma
    • Burns
    • Myositis
  • Pigmenturia; causes include:
    • Porphyria
    • Urate
    • Beets
    • Drugs e.g. rifampicin

NEPHROTIC SYNDROME

It is characterised by proteinuria, oedema, hypoalbuminaemia and hypercholesterolaemia.

Pathophysiology

Nephrotic syndrome is due to glomerular or tubular disruption which impairs the basement membrane proteins and effects of their negative charge, making the basement membrane more permeable to serum proteins. This leads to a decrease in serum protein, decreased oncotic pressure and the shift of fluid into the interstitium. The effective decrease in plasma volume results in the activation of RAAS, which retains more fluid and leads to the shifting of even more fluid into the interstitium. Lastly, hepatic lipoprotein synthesis is activated and there is a resultant increase in triglycerides and cholesterol.

Aetiology

Nephrotic syndrome may be:

Clinical Features

The child may present with:

Investigations

The following investigations should be performed:

Other tests which may be performed to diagnose a secondary cause:

Management

General Measures

The child should be put on a diet with restricted sodium and saturated fat restriction. However, fluids should not be restricted. The diet must maintain nutrition and contain sufficient multivitamins, calcium and folic acid. Daily weights, BP, dipsticks and UPCRs should be done.

Prophylaxis against secondary infections should be given. If the child has anasarca, phenoxymethylpenicillin should be administered, as these patients are at risk of pneumococcal peritonitis. The child should also be given the routine vaccinations against pneumococcus, VZV and HBV according to the EPI, once s/he is in remission and not on steroids or immunosuppressive therapy.

Specific Management

The child with idiopathic nephrotic syndrome should be started on empiric steroid therapy (prednisone 2 mg/kg up to maximum of 60 mg) for a minimum of 4-6 weeks. In secondary nephrotic syndrome, the underlying illness needs to be treated.

Mild oedema will improve with conservative management and steroids (if the nephrosis is steroid-responsive). Resistant oedema may be cautiously treated with diuretics and severe anasarca may require an albumin infusion. Enalapril, chronic diuretics and statin therapy are only indicated in steroid-resistant cases and should be given under specialist supervision.

ACUTE KIDNEY INJURY (AKI)

Pathophysiology

AKI is characterised by an abrupt decline in the glomerular filtration rate (GFR) and tubular function, resulting in decreased excretion of creatinine, urea, nitrogen, phosphate and fluid. This child will, therefore, be azotaemic and fluid overloaded with normal, decreased or increased urine output.

Aetiology

AKI may have a pre-, intra- or post-renal cause.

Table 17.2: Pre-, Intra- and Postrenal Causes of AKI

Pre-Renal AKI Intrarenal AKI Post-Renal AKI
  • Dehydration
  • Septic shock
  • Heart failure
  • Haemorrhage
  • Burns
  • Renal artery or vein issues
  • Acute tubular necrosis
  • Nephrotoxins
  • Glomerulonephritis
  • Acute cortical necrosis
  • Interstitial nephritis
  • Infection
    		•
    • Urethral obstruction
    • Ureteral obstruction
    • Extrinsic compression of outlet e.g. tumour
    • Neurogenic bladder

    Clinical Features

    The child may present with:

    One must examine the child for features of genetic syndromes associated with renal disease e.g. Down syndrome, FASD

    Investigations

    They should include:

    Management

    General Measures

    One must identify and manage the cause(s) e.g. relieve obstruction in post-renal AKI, treat active infection. Adequate perfusion and fluid balance must be maintained (replace fluid losses and restrict fluid intake as needed). Feeding must be maintained and the child placed on sodium-, potassium- and phosphate-restricted, high-protein diet. Daily weights, BP and dipstick checks should be done.

    Specific Management

    One must manage:

    Dialysis (peritoneal dialysis or haemodialysis) is indicated when the above-mentioned issues become refractory or the child has been poisoned with a dialysable agent.

    HAEMOLYTIC URAEMIC SYNDROME (HUS)

    Pathophysiology and Aetiology

    There are many types of HUS but the most common type is associated with a prodromal diarrhoeal phase. HUS typically occurs 7-10 days after a diarrhoeal illness caused by bacteria which secrete Shiga or verotoxins e.g. Shigella sp. or E. coli, respectively. The toxin binds to and damages glomerular endothelial cells, resulting in coagulation.

    If severe, glomerular and interstitial thrombosis and haemolysis result (RBCs are squeezed through the narrowed vessel lumens). Thus, HUS presents with the triad of microangiopathic haemolytic anaemia, thrombocytopenia and acute renal injury (haematuria or renal failure).

    Clinical Features

    The child may present with:

    Investigations

    They should include:

    Management

    It is supportive and includes:

    URINARY TRACT OBSTRUCTION

    It is a common condition which can occur at any anatomical level of the genitourinary tract.

    Aetiology and Pathophysiology

    Common congenital causes of urinary tract obstruction are:

    The obstruction may be:

    Clinical Features

    The child may present with:

    Investigations

    They should include:

    Management

    The obstruction must be relieved as soon as possible with a catheter. One must exclude or manage dysfunctional voiding or a neurogenic bladder. Current infections should also be treated. Prophylactic antibiotics may be indicated in patients with recurrent infections and/or abnormal anatomy. Regular dipsticks and RFTs should be done. Surgery may be required to correct any anatomical anomalies.

    NEPHROLITHIASIS (RENAL STONES)

    Nephrolithiasis is the formation of a precipitate in the genitourinary system.

    Pathophysiology

    It may be due to:

    Clinical Features

    The child may present with:

    Investigations

    They should include:

    Management

    General management includes:

    HYPOSPADIAS

    It forms part of a triad of congenital anomalies:

    It is associated with genital ambiguity rather than urinary anomalies.

    Clinical Features

    The child may have:

    Investigations

    The diagnosis is clinical and investigations are usually unnecessary.

    Management

    Surgical intervention before 18 months of age is best.

    CHRONIC KIDNEY DISEASE (CKD)

    It refers to continuous injury to the kidneys that results in progressive decline in kidney function until end stage renal failure develops.

    Aetiology

    Causes include congenital and obstructive diseases. After puberty, acquired conditions and the inability to support the growing body become more common causes of chronic renal failure.

    Clinical Features

    They may include:

    Investigations

    They should include:

    Management

    A multidisciplinary approach should be used. Treatment should include:

    The child must be assessed for the need for chronic dialysis or renal transplantation.

    PAEDIATRIC HYPERTENSION (HPT)

    This is defined as systolic or diastolic BP >95th percentile for age, sex and height. There is an increased risk of sequelae with severe or chronic hypertension. The HPT may be due to:

    Clinical Features

    Children are usually asymptomatic but can present with target organ damage. The child may have:

    Investigations

    One should perform investigations which help one assess target organ damage, assess cardiovascular risk factors and identify causes. Further focused investigation should be done based on initial findings.

    Management

    It includes: