Introduction

The nephritic syndrome is the name given to a cluster of symptoms and signs. It can be caused by a number underlying pathologies affecting the kidneys, but in itself is not a diagnosis. These diseases lead to inflammation in the glomeruli (glomerulonephritis), the kidneys filtering units. Patients tend to present acutely, and can be very unwell requiring rapid intervention.

It is a separate entity from nephrotic syndrome, in which dysfunction of the basement leads to the leakage of protein into the urine resulting in proteinuria, hypoalbuminaemia, and oedema.

    Signs and Symptoms

    • Haematuria (this can be 'visible' to the naked eye, or 'not visible' when it is detected on urine dipstick)
    • Proteinuria (this is typically less than is seen in nephrotic syndrome)
    • Hypertension
    • Oedema (often periorbital, as well as dependent e.g. ankle and sacral)
    • Uraemia (symptoms of this include lethargy, pruiritis, nausea and vomiting)
    • Oliguria

    Pathophysiology

    Damage to the glomerulus occurs by an immune-mediated injury. This inflammatory reaction is started either by an antibody targeted at a component of the glomerulus, such as in anti-GBM disease when the target is the basement membrane. Or because immune complexes generated elsewhere in the body are trapped by glomerular filtration, as occurs in post-streptococcal glomerulonephritis (PSGN). These antibodies/immune complexes in turn lead to the activation of the complement cascade and infiltration of inflammatory cells. The exact mechanism of injury depends on the underlying disease process but the following histologic features are common:

     

    1. Proliferation of cells within glomerulus; mesangial cells (macrophages of the kidney), endothelial cells reducing capillary lumen diameter, and epithelial cells with Bowman's space given rise to crescent formation.
    2. Infiltration of inflammatory cells; neutrophils, macrophages etc.
    3. Basement membrane thickening; caused by deposition of antibodies, immune complexes and complement.

     

    These changes can affect some (segmental) or all (global) of the glomerulus, and can affect some (focal) or all (diffuse) of the glomeruli within the kidneys.

     

    As a result the filtration capabilities of the glomerulus are affected. The glomerular basement membrane is damaged and it thus allows protein and red blood cells to leak through. As these transit through the nephron casts can be formed. Light microscopy of the patients urine may be used to detect these, and they are pathognomic of glomerular disease. Glomerular filtration rate is reduced stimulating the retention of salt and water culminating in hypertension and oedema. As there is decreased filtering of the blood, levels of waste products rise resulting in azotemia, and the production of urine falls (oliguria).

    Focal Segmental GN seen in ANCA positive disease



    In this disease, not all glomeruli are affected (focal), and of those that are affected not all of the glomerulus is involved (segmental). There has been a proliferation of cells within Bowman's space taking the form of a crescent, this is the reason for the alternative name of crescenteric glomerulonephritis.

    (adapted from J.Charles Jennette, www.unckidneycenter.org)

     

    Diseases causing nephritic syndrome

    As stated a number of diseases can cause the nephritic syndrome:

     

    Post-Streptococcal Glomerulonephritis (PSGN):

    • Typically affects children in the developing world, now rare in developed countries.
    • Infection with Lancefield group A Beta-haemolytic streptoccocus presenting as sore throat, otitis media, cellulitis etc. responsible.
    • Renal disease has latent interval of 2-4 weeks reflecting the time taken for immune complex formation and deposition in the glomerulus.

     

      Non-Streptococcal post-infectious GN:

      • Seen after multitude of infections including mumps, measles, infectious mononucleosis, malaria, schistosomiasis.

       

          Rapidly Progressive Glomerulonephritis (RPGN):

           In itself caused by different underlying pathologies;

          • ANCA +ve vasculitis e.g. Wegener's granulomatosis, Microscopic polyangiitis
          • Immune complex deposition disease secondary to SLE, IgA nephropathy, Henoch-Schonlein Purpura (a common cause in children)
          • Anti-GBM disease (Goodpasture's syndrome)

           

          IgA nephropathy:

          • Deserves mention on its own as it is the commonest cause of the nephritic syndrome in adults.
          • Tends to occur acutely (24-48h) after respiratory tract or GI tract infection.

           

          Haemolytic Uraemic Syndrome:

          • Most commonly seen in children after E.Coli 0157 infection.

           

          Membranoproliferative GN:

            • Another umbrella term like RPGN.
            • Can be autoimmune in origin secondary to SLE, scleroderma, Sjogren's syndrome
            • Occur secondary to malignancies such as leukaemias and lymphomas

             

            Infective Endocarditis

            Abdominal abscess

               

              For more information of the various glomerulonephritidies, please consult the article on glomerulonephritis.

                Management

                The goal of treatment is two-fold.

                1. Manage acute derangements in electrolytes, blood pressure etc.
                2. Reduce underlying inflammation in the kidney.

                 

                  Treatment targeted at addressing glomerular inflammation will vary depending on the underlying disease etiology, and is not within the scope of this article.

                   

                  Acute phase management will depend on the patient's parameters, but is likely to include:

                  • Fluid restriction +/- diuretics to manage oedema
                  • Control of BP with antihypertensives
                  • Restriction of sodium +/- potassium
                  • Dialysis if indicated, such as refractory hyperkalemia, symptomatic uraemia, acidosis.

                   

                  Once the patient is stable, it is reasonable to undertake investigations in order to identify the underlying cause and manage it appropriately. This is likely to include:

                  • Urinanalysis
                  • Immunological tests; ANA, ANCA, C3/4, anti-GBM Ab
                  • Blood cultures/throat swabs if infectious cause suspected
                  • Renal biopsy

                   

                    Prognosis

                    This is related to the underlying pathology of the nephritic syndrome, and varies widely. As stated, nephritc syndrome is not a diagnosis.

                    References

                     

                    http://www.unckidneycenter.org/index.html.

                    http://emedicine.medscape.com/article/239278-overview.

                    Kumar, P. & Clark, M. Clinical medicine. 8th ed; Edinburgh: Elsevier Saunders.

                     

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