Lupus nephritis: nephritic, nephrotic or mixed
Lupus nephritis is the kidney disease of systemic lupus erythematosus (SLE), in which immune complexes (clumps of antibody and antigen) are deposited in the glomeruli, the tiny filters.
Remember
Lupus nephritis can be nephritic (inflamed filters, with blood in the urine), nephrotic (leaky filters, with heavy protein loss) or a mixture, so consider SLE in any unexplained nephritic or nephrotic syndrome.
Memory aid
think of lupus as a chameleon in the kidney: the same disease can look nephritic or nephrotic
A chameleon changes its appearance, just as lupus nephritis can look nephritic, nephrotic or a mixture.
In SLE the body makes autoantibodies (antibodies against its own tissues), mainly against nuclear material such as DNA. These bind their targets and form immune complexes, which circulate and become trapped in the glomeruli. There they activate complement (a chain of blood proteins that tags targets and draws in inflammatory cells), so the filter becomes inflamed and damaged. This is lupus nephritis.
Where the complexes land, and how severe the damage is, shape the picture. Deposits on the inner, blood side of the filter tend to cause a nephritic picture: haematuria (blood in the urine), hypertension and falling kidney function. Deposits on the outer side, beneath the podocytes (the cells that wrap around the capillaries), tend to cause protein leak and a nephrotic picture: heavy proteinuria (protein loss in the urine), low albumin and oedema (fluid swelling in the tissues). Some patients have both.
How the filters are injured varies between patients. Kidney disease can be the first sign of SLE, and it may even be the only manifestation, so lupus should be kept in mind in any patient with an unexplained nephritic or nephrotic syndrome. A renal biopsy classifies the disease and guides treatment.
Key facts
- Mechanism
- immune complexes deposit in the glomeruli and activate complement and cause inflammation.
- Patterns
- lupus nephritis can present as nephritic syndrome, nephrotic syndrome or a mixture.
- Nephritic features
- haematuria, hypertension and falling kidney function, from inflamed glomeruli.
- Nephrotic features
- heavy proteinuria, low albumin and oedema, from a leaky filter.
- Where deposits land
- whether the pattern is nephritic, nephrotic or mixed depends on the site of deposition and on how severe the damage is.
- Diagnosis
- renal biopsy classifies the disease and guides treatment.
Exam traps
- Nephritic syndrome with linear deposits of IgG (an antibody) in the glomeruli is characteristic of anti-glomerular basement membrane disease (the basement membrane is the supporting layer of the filter), whereas lupus nephritis instead has granular immune complex deposits (clumps of antibody and antigen).
- Minimal change disease is the classic cause of heavy protein loss with little inflammation, but lupus nephritis is not confined to a pure nephrotic picture, because its commonest forms usually add haematuria and often hypertension.
- Autoantibodies binding directly to type IV collagen in the glomerular basement membrane (the supporting layer of the filter) describe anti-GBM disease (Goodpasture's disease), whereas lupus damages the glomeruli through circulating immune complexes.
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