Using light microscopy, the volume of the glomerulus was increased, and substantial amounts of PAS and fuchsinophilic
materials were present in the mesangial area.
Subepithelial deposits, when present in substantial amounts, appear by trichrome stain as fuchsinophilic
granules on the outer aspect of glomerular basement membrane.
Biopsy specimens, taken both from patients and inoculated guinea pigs, demonstrated "small intracellular fuchsinophilic
granules and rods, similar in morphology to Rickettsiae.
Five microscopic features are seen: (a) compressed remnants of lymphoid tissue at the periphery; (b) spindle cells with nuclear palisading; (c) intraparenchymal hemorrhage and erythrocyte extravasation; (d) so-called amianthoid fibers; and (e) intracellular and extracellular fuchsinophilic bodies that stain positive for smooth muscle actin.
The fifth histological feature of IPM is extracellular and intracellular fuchsinophilic bodies.