Renal diseases with organized deposits: an algorithmic approach to classification and clinicopathologic diagnosis.

CONTEXT: Most renal diseases with organized deposits are relatively uncommon conditions, and proper pathologic characterization determines the specific diagnosis. Different entities with specific clinical correlates have been recognized, and their correct diagnosis has an impact on patient management, treatment options, and determination of prognosis.

OBJECTIVE: The diagnosis of these conditions depends on careful evaluation of the findings by light microscopy together with immunofluorescence and electron microscopy. The objective of this manuscript is to delineate an algorithmic approach helpful in the pathologic assessment of these conditions at the light microscopic level. In some diseases, the immunomorphologic parameters short of electron microscopy provide solid information to suggest or make a definitive diagnosis. Nevertheless, electron microscopy plays a crucial role, because the criteria to separate these entities often are heavily influenced by the electron microscopic findings. Accepted diagnostic criteria for each of these conditions are discussed.

DESIGN: Information used for this manuscript is gathered from published data and the authors' experience.

RESULTS: The most common of these conditions is amyloidosis, which may account for as many as 5% to 8% of all renal biopsies in some renal pathology practices. Fibrillary, immunotactoid, and cryoglobulinemic glomerulopathies together represent, at most, 1% of all renal biopsies performed for medical renal diseases. Diabetic fibrillosis also is uncommon. Glomerulopathies associated with fibronectin deposits and collagenofibrotic glomerulopathy are extremely rare.

CONCLUSIONS: A systematic, algorithmic approach to the evaluation of the renal biopsies from patients with these disorders is very helpful to rule out certain conditions in the early stages of the evaluation of the biopsies. However, it is not uncommon for the final definitive diagnosis to be reached only after electron microscopic evaluation.