Everyone has a certain diagnosis in Nephrology that is just hard to understand. For me, it has been the diagnosis of MPGN (membranoproliferative glomerulonephritis). After extensive reading, I have developed a couple of pearls and interesting points that I would like to share with you.
First: you can add MPGN to any differential diagnosis of kidney disease you have, since the presentation can range from nephritic syndrome, isolated proteinuria, isolated hematuria to nephrotic syndrome.
Second: In order to develop MPGN, you have to have damage to the endothelium of the glomeruli in one of the following ways:
– Chronic subendothelial immunecomplex deposition from persistent antigenemia, like in HCV, HBC or bacterial endocarditis. Or persistent deposition of immunecomplexes in autoimmune diseases like SLE;
– Chronic thrombotic microangiopathy like in TTP/HUS or antiphospholipid syndrome
– Monoclonal immunoglobulin deposition disease like in multiple myeloma.
Third: there is usually consumption of complements (low C4 and C3)
Fourth: the term MPGN is only helpful in defining the pattern of injury characterized by the thickened GBM and the hypercellularity. Think about potential causes of damage to the endothelium when approaching your differential.
Fifth: it has been recently demonstrated that the mesangial cells are not responsible for the ‘tram-track’ appearance as you may find in numerous books. The additional basement membrane is formed by the endothelium, displaced by the presence of subendothelial immune deposits and cell projections derived from endothelium cells and infiltrating macrophages.
Lastly, nephrologists decided to name a completely different disease type II MPGN – also called dense deposit disease. Different because its etiology involves abnormal activation of the alternative complement pathway usually in kids, C3 is low while C4 is normal (postStrep GN also) and diagnosis requires EM (electro-dense material).