Immunotactoid (microtubular) glomerulopathy: an entity distinct from fibrillary glomerulonephritis?

Immunotactoid glomerulopathy (IT), or alternatively, microtubular glomerulopathy, is a term that has been used by some investigators to encompass those glomerulopathies characterized by the presence of fibrillar or microtubular deposits which are distinguished from amyloid principally by their larger size and lack of reactivity with the Congo red reagent. A case is presented here of IT as it was initially described. The present case, and a review of the literature, suggest that the diagnosis of IT be restricted to those glomerulopathies associated with large, at times organized, microtubular deposits. Terms such as fibrillary glomerulonephritis, or alternatively Congo red-negative amyloidosis-like glomerulopathy, could then be used to describe those patients with smaller, fibrillar glomerular deposits having an appearance closely resembling amyloid. We believe it is possible to separate the entities fibrillary glomerulonephritis and IT on morphological grounds. This is a potentially useful distinction that identifies patients who are likely to have or develop clinical evidence of a lymphoplasmacytic disorder or dysproteinemia, which are associated with deposits of IT, and distinguishes them from patients with fibrillary glomerulonephritis, of whom only a single case has been linked to such clinical findings.