(See also Overview of Nephritic Syndrome.)
IgA nephropathy is a nephritic syndrome, a form of chronic glomerulonephritis characterized by the deposition of IgA immune complexes in glomeruli. It is the most common form of glomerulonephritis worldwide. It occurs at all ages, with a peak onset in the teens and 20s; affects men 2 to 6 times more frequently than women; and is more common in whites and Asians than in blacks. Prevalence estimates for IgA kidney deposits are 5% in the US, 10 to 20% in southern Europe and Australia, and 30 to 40% in Asia. However, some people with IgA deposits do not develop clinical disease.
Cause is unknown, but evidence suggests that there may be several mechanisms, including
Familial clustering has also been observed, suggesting genetic factors at least in some cases.
The most common manifestations are persistent or recurrent macroscopic hematuria or asymptomatic microscopic hematuria with mild proteinuria. Flank pain and low-grade fever may accompany acute episodes. Other symptoms are usually not prominent.
Gross hematuria usually begins 1 or 2 days after a febrile mucosal (upper respiratory, sinus, enteral) illness, thus mimicking acute postinfectious glomerulonephritis, except the onset of hematuria is earlier (coinciding with or immediately after the febrile illness). When this occurs with an upper respiratory illness, it is sometimes referred to as synpharyngitic hematuria.
Rapidly progressive glomerulonephritis is the initial manifestation in < 10% of patients.
Diagnosis is suggested by any of the following:
Gross hematuria, particularly within 2 days of a febrile mucosal illness or with flank pain
Incidentally noted findings on urinalysis
Occasionally, rapidly progressive glomerulonephritis
When manifestations are moderate or severe, diagnosis is confirmed by biopsy.
Urinalysis demonstrates microscopic hematuria, usually with dysmorphic red blood cells (RBCs) and occasionally RBC casts. Mild proteinuria (< 1 g/day) is typical and may occur without hematuria; nephrotic syndrome develops in ≤ 20%. Serum creatinine level is usually normal.
Renal biopsy shows granular deposition of IgA and complement (C3) on immunofluorescent staining in an expanded mesangium with foci of segmental proliferative or necrotizing lesions. Importantly, mesangial IgA deposits are nonspecific and also occur in many other disorders, including immunoglobulin A–associated vasculitis, cirrhosis, inflammatory bowel disease, celiac disease, psoriasis, HIV infection, lung cancer, and several connective tissue disorders.
Glomerular IgA deposition is a primary feature of immunoglobulin A–associated vasculitis, and it may be indistinguishable from IgA nephropathy based on biopsy specimens, leading to speculation that immunoglobulin A–associated vasculitis may be a systemic form of IgA nephropathy. However, immunoglobulin A–associated vasculitis is clinically distinct from IgA nephropathy, usually manifesting as hematuria, purpuric rash, arthralgias, and abdominal pain.
Other serum immunologic tests are usually unnecessary. Complement concentrations are usually normal. Plasma IgA concentration may be elevated, and circulating IgA-fibronectin complexes are present; however, these findings are not helpful diagnostically.
IgA nephropathy usually progresses slowly; renal insufficiency and hypertension develop within 10 years in 15 to 20% of patients. Progression to end-stage renal disease occurs in 25% of patients after 20 years. When IgA nephropathy is diagnosed in childhood, prognosis is usually good. However, persistent hematuria invariably leads to hypertension, proteinuria, and renal insufficiency. Risk factors for progressive deterioration in renal function include the following:
Often angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) for hypertension, serum creatinine > 1.2 mg/dL (106.08 micromol/L), or macroalbuminuria (urinary protein > 300 mg/day) and with a target urinary protein of < 500 mg/day
Corticosteroids for progressive disease, including increasing proteinuria especially into the nephrotic range, or increasing serum creatinine level
Corticosteroids and cyclophosphamide for proliferative injury or rapidly progressive glomerulonephritis
Transplantation in advanced disease
Normotensive patients with intact renal function (serum creatinine < 1.2 mg/dL [106.08 micromol/L]) and only mild proteinuria (< 0.5 g/day) usually are not treated beyond angiotensin inhibition (with an ACE inhibitor or ARB) and omega-3 fatty acids (fish oil). Patients with renal insufficiency or more severe proteinuria and hematuria are usually offered treatment, which ideally should be started before significant renal insufficiency develops.
ACE inhibitors or ARBs are used on the premise that they reduce blood pressure, proteinuria, and glomerular fibrosis. Patients with the DD genotype for the ACE gene may be at greater risk of disease progression but may also be more likely to respond to ACE inhibitors or ARBs. For patients with hypertension, ACE inhibitors or ARBs are the antihypertensives of choice even for relatively mild chronic kidney disease.
Corticosteroids have been used for many years, but benefit is not well documented. One protocol uses methylprednisolone 1 g IV once a day for 3 days at the beginning of months 1, 3, and 5 plus prednisone 0.5 mg/kg orally every other day for 6 months. Another regimen uses prednisone beginning 1 mg/kg orally once a day with dose gradually tapered over 6 months.
Because of the risk of adverse effects, corticosteroids should probably be reserved for patients with any of the following:
Combinations of IV corticosteroids and cyclophosphamide plus oral prednisone are used for severe disease, such as proliferative or crescentic (rapidly progressive) nephropathy. Evidence for mycophenolate mofetil is conflicting; it should not be used as first-line treatment. None of these drugs, however, prevents recurrence in transplant patients. Immunosuppressive therapy should also be avoided in patients with advanced fibrotic kidney disease, which is not reversible.
Omega-3 polyunsaturated fatty acids (eg, 4 to 12 g/day), available in fish oil supplements, have been used to treat IgA nephropathy, but data on efficacy are contradictory. Mechanism of effect may include alterations in inflammatory cytokines.
Other interventions have been tried to lower IgA overproduction and to inhibit mesangial proliferation. Elimination of gluten, dairy products, eggs, and meat from the diet; tonsillectomy; and immune globulin 1 g/kg IV 2 days a month for 3 months followed by immune globulin 0.35 mL/kg of 16.5% solution IM every 2 weeks for 6 months all theoretically reduce IgA production. Heparin, dipyridamole, and statins are just a few examples of in vitro mesangial cell inhibitors. Data supporting any of these interventions are limited or absent, and none can be recommended for routine treatment.
Kidney transplantation is better than dialysis because of excellent long-term disease-free survival. The condition recurs in ≤ 15% of graft recipients.
IgA nephropathy is the most common cause of glomerulonephritis worldwide and is common among young adults, whites, and Asians.
Consider the diagnosis in patients with unexplained signs of glomerulonephritis, particularly when it occurs within 2 days of a febrile mucosal illness or with flank pain.
Treat patients who have creatinine > 1.2 mg/dL (106.08 micromol/L) or proteinuria > 300 mg/day with ACE inhibitors or ARBs.
Reserve corticosteroids for patients with worsening renal function or proteinuria (> 1 g/day) despite maximal ACE inhibitor or ARB treatment.
Treat patients who have proliferative injury or rapidly progressive glomerulonephritis with corticosteroids and cyclophosphamide.