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Morphologic variations of dense deposit disease: Light and electron microscopic, immunohistochemical and clinical findings in 10 patients

Twenty‐one renal biopsy specimens obtained from 10 patients with dense deposit disease (DDD) were investigated using light microscopy, electron microscopy and immunohistochemistry. The patients included four females and six males aged 6 to 35 years (mean 16.1 years). A morphological diagnosis of DDD was made following the ultrastructural detection of continuous intramembranous dense deposits (CIMDD) in some capillary loops of at least one of the series of the repeated biopsies from each patient. With light microscopy, six patients showed membranoproliferative glomerulonephritis (MPGN). The other four patients showed diffuse proliferative glomerulonephritis (DPGN) with acute lesions showing intraglomerular neutrophilic infiltration, hump formation and endothelial swelling in three and minor glomerular abnormalities in one. Follow‐up biopsies were obtained in six patients. Two patients progressed from DPGN to MPGN within 7 months, whereas three patients with MPGN showed morphologic improvement that featured increased capillary patency and regional disappearance of dense deposits along with the reduction of proteinuria. Dense deposit disease did not always feature typical amorphous and osmiophilic CIMDD spreading across the whole width of the lamina densa. This classical ultrastructural manifestation was mainly found in the patients with histologic non‐MPGN and a linear peripheral pattern of complement component (C3) deposition. The MPGN patients with a granular peripheral pattern of C3 deposition also had CIMDD, but also additionally featured less dense subepithelial deposits superimposed on the CIMDD to produce an appearance simulating membranous transformation. Humplike epimembranous massive dense deposits were also identified in connection with the deposition of immunoglobulin G (IgG), suggesting that immune complex deposition at the glomerular basement membrane occurs in some cases of DDD. Immunoglobulin M (IgM) or complement component 1q (C1q) deposition was often associated with intraglomerular neutrophilic infiltration and endothelial swelling as well as with ultrastructural subendothelial edema. Continuous dense deposits were found not only in the lamina densa but also just beneath the subendothelium in four patients. Thus, the present investigation demonstrated the morphologic variety of DDD in a correlative study of light microscopy, electron microscopy and immunohlstochemistry.