IgA nephritis
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IgA nephritis (also known as Berger's disease and synpharyngitic glomerulonephritis) is a form of glomerulonephritis (inflammation of the glomeruli of the kidney). It presents with hematuria and generally resolves spontaneously, but a proportion of patients develops chronic renal failure. IgA is the antibody which accumulates in the kidney and probably plays a central role in the disease.
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Signs and symptoms
The classic presentation (in 40-50% of the cases) is frank hematuria which starts one or more days after an upper respiratory tract infection (sore throat). Flank pain can occur. The hematuria resolves after a few days. These episodes occur on an irregular basis, and in most patients, this eventually stops (although it can take many years).
A smaller proportion (20-30%) has microscopic hematuria and proteinuria (less than 2 gram of protein per 24 hours). These patients can have mild symptoms and are only picked up if a doctor decides to take a urine sample.
Very rarely (5% each), the presenting history is:
- Nephrotic syndrome (excessive protein loss in the urine)
- Acute renal failure (generally a complication of the hematuria)
- Chronic renal failure (no previous symptoms, presents with anemia, hypertension and other symptoms of renal failure)
IgA-nephritis can occur in the context of liver failure, coeliac disease, rheumatoid arthritis, Reiter's disease, ankylosing spondylitis and HIV. Occasionally, there are simultaneous symptoms of Henoch-Schönlein purpura; see below for more details on the association.
Diagnosis
The history and association with respiratory infection can raise the suspicion IgAN. A urinary specimen can confirm the suspicion (red blood cells, sometimes in cylinders), but in order to completely determine the cause, a kidney biopsy is necessary (generally performed under local anaesthetic). The biopsy specimen shows proliferation of the mesangium and occasional crescentic changes (see below).
Blood tests that are generally performed before the biopsy are: full blood count, coagulation (APTT, PT), CRP or ESR, electrolytes, renal function (creatinine, urea), total protein, albumin, LDH. Protein electrophoresis and immunoglobulin levels can show increased IgA1 in up to 30% of all patients. Complement levels can be decreased.
Ultrasound of the kidney is generally performed at some stage in the diagnostic tract.
Differential diagnosis: other diseases that cause episodic hematuria are kidney stones, bladder cancer and Alport's disease. Post-streptococcal glomerulonephritis occurs longer after the throat infection and presents differently (see there).
Pathophysiology
The disease derives its name from deposits of Immunoglobulin A (IgA) in a blotchy pattern in the mesangium (on immunofluorescence), the heart of the renal glomerulus. As a rule, this affects the whole kidney. The tissue changes gradually from being hypercellular to depositing extracellular matrix proteins, and finally fibrosis.
There is no clear known explanation for the accumulation of the IgA. Exogenous antigens for IgA have not been identified in the kidney, but it is possible that this antigen has been cleared before the disease manifests itself.
A recently advanced theory focuses on abnormalities of the IgA1 molecule. IgA1 is one of the two immunoglobulin subclasses (the other is IgD) that is O-glycosylated on a number of serine and threonine residues in a special proline-rich hinge region. Deficiency of these sugars appears to lead to polymerisation of the IgA molecule in tissues, especially the glomerular mesangium. A similar mechanism has been claimed to underly Henoch-Schönlein purpura (HSP), a vasculitis that mainly affects children and can feature renal involvement that is almost indistinguishable from IgA nephritis.
From the fact that IgAN can recur after renal transplant it can be postulated that the disease is caused by a problem in the immune system rather than the kidney itself. Remarkably, the IgA1 that accumulates in the kidney does not appear to originate from the mucosa-associated lymphoid tissue (MALT), which is the site of most upper respiratory tract infections, but from the bone marrow. This, too, suggests an immune pathology rather than direct interference by outside agents.
Therapy
There is no curative therapy for IgAN. People with a known propensity often have their renal function monitored once every few months, to identify chronic renal failure if this occurs. Tonsillectomy (to decrease the amount of infections) is not effective in slowing down any long-term kidney damage, although attack frequency decreases.
Proteinuria responds to ACE inhibitor therapy, and some studies indicate favorable response to prednisolone.
Genetics
Virtually all cases are sporadic, although a family in Kentucky has been described where IgAN occurs in a familial pattern (Template:OMIM).
Prognosis
Episodes of hematuria recur with variable frequency in most patients, but this generally resolves over a number of years. This can take a long time: after 10 years, 30% has ceased having attacks. Strangely, the classic form (episodic hematuria) has a good prognosis.
Up to 25% develops chronic renal failure within 20 years of diagnosis. Unfortunately, the disease can recur after renal transplant, potentially damaging the graft.
Epidemiology
Males are affected three times as often as women. For an unknown reason, it occurs more often in Meditteranian and Pacific countries than in Northern Europe and America. Kaukasians are most often affected, while Afro-Caribbeans and Polynesians rarely are, even when they live in Westernised countries. This argues in favour of a genetic cause.
History
The disease was first described in French in 1968: Berger J, Hinglais N. Les depots intercapillaires d'IgA-IgG. J Urol Nephrol 1968;74:694-5.
Sources
- Oxford Textbook of Medicine