Immuotactoid Glomerulopathy (Fibrillary Glomerulonephritis)

Abstract

Immunotactoid glomerulopathy first was described in 1977, when Rosenmann and Eliakim (1) reported an unusual glomerular lesion in a 45-yr-old woman who presented with the nephrotic syndrome and renal insufficiency. The electron microscopy was remarkable for organized electron-dense deposits in the form of randomly arranged fibrils that measured 10 nM in diameter. The deposits were associated with mesangial expansion and immune deposits of IgG, IgM, and C3 in a mesangial pattern. Congo red stain of the deposits was negative, and there was no clinical or serologic evidence of a systemic disease. They interpreted the deposits to be “amyloid-like” and speculated that they might represent a “preamyloid” state. In 1980, Schwartz and Lewis (2) reported a case of a 49-yr-old man who presented with the nephrotic syndrome and no evidence of systemic disease and had a similar renal lesion: Immune aggregates were associated with highly organized electron-dense deposits that were composed of microtubules that were arranged in parallel bundles. During 7 yr of follow-up, the patient progressed to renal failure but never demonstrated any clinical or serologic evidence of a systemic disease. To distinguish this lesion from other disorders that have glomerular immune deposits associated with highly organized microtubular or fibrillary structures, such as amyloidosis, cryoglobulinemia, paraproteinemias, and systemic lupus erythematosus (SLE), the term immunotactoid glomerulopathy (ITG) was coined, reflecting the composition (immuno-) and polymeric morphology (tactoid) of the glomerular deposits. In the past 25 yr, >200 cases of ITG have been reported (3–5). Various synonyms have been used to refer to the lesion that is described in these reports, including fibrillary glomerulonephritis (FGN), nonamyloidotic fibrillary glomerulopathy, amyloid-like glomerulopathy, and amyloid stain–negative microfibrillary glomerulopathy, but we believe that they all represent the same or a similar disease process (6–8). The unifying feature in all of the cases …