The pathologic finding of MPGN is an uncommon finding in chronic nephropathy affecting children and adults. Patients with MPGN present with hematuria, dysmorphic red blood cells or red blood cell casts, varying degrees of proteinuria, and elevation in serum creatinine. Overall, it is more common in children and in underdeveloped nations.
The characteristic renal biopsy findings on light microscopy are mesangial hypercellularity, endocapillary proliferation, and double-contour formation along the glomerular capillary walls. Two primary classifications are seen based on the pattern of staining on light microscopy: immune complex mediated and complement mediated.
Immune complex-mediated MPGN is either primary (idiopathic) or secondary to an underlying chronic infection, autoimmune disease, or monoclonal gammopathy that leads to antigenemia and/or circulating immune complexes that deposit in the mesangium. Immune complex deposition in the mesangium results in both complement and inflammatory cell activation. As a result of this inflammation, the glomerulus responds by proliferating and attempting to create a new basement membrane; hence the "double contour" or "tram tracking" classically seen on light microscopy. Mesangial thickening arises from monocyte infiltration and responding increase in both mesangial cells and mesangial thickening.
Idiopathic etiology is the most common cause of immune complex-mediated MPGN. Common infectious causes of secondary immune complex-mediated MPGN include hepatitis B and hepatitis C, bacterial endocarditis, and parasitic infections. Common autoimmune causes include systemic lupus erythematosus, Sjögren syndrome, scleroderma, rheumatoid arthritis, and mixed cryoglobulinemia. Patients with monoclonal gammopathy, such as monoclonal gammopathy of undetermined significance (MGUS) or multiple myeloma, may present with proteinuria and worsening renal function. Other myeloproliferative disorders implicated in immune complex-mediated MPGN include chronic lymphocytic leukemia and low-grade B-cell lymphoma (see non-Hodgkin lymphoma).
Complement-mediated MPGN is less common than immune complex-mediated MPGN. Complement-mediated MPGN is often caused by dysregulation and persistent activation of the alternative complement pathway, leading to deposition of complement products along the capillary walls and in the mesangium that results in bright C3 staining in these locations. It is commonly associated with a circulating autoantibody known as C3 nephritic factor, which binds to the C3 convertase, which stabilizes it and leads to its persistent activation.
Diseases include dense deposit disease (DDD), in which damage results from antibodies that bind to C3 convertase; it is seen in both adults and children. Patients with C3 glomerulonephritis (C3GN) present with proteinuria, hematuria, and hypertension from overactivation of the complement cascade.
N05.5 – Unspecified nephritic syndrome with diffuse mesangiocapillary glomerulonephritis
80321008 – Membranoproliferative glomerulonephritis