Pitfalls in the Pathological Diagnosis of Glomerular Diseases: Why Stop at One?

Background: Renal pathologists face a number of challenges in evaluating kidney biopsies: one that is sometimes overlooked is the presence of multiple pathological processes in a single biopsy. Figuring out the interrelatedness (or lack thereof) of more than one form of renal abnormality can difficult. Several pitfalls in biopsy evaluation also await the unprepared diagnostician. This communication will examine these problems with illustrations from a single nephropathology practice dating back more than 3 decades. Summary: Paired processes in a biopsy can be related in many ways, including 2 lesions with a single root cause, 1 lesion that is a direct consequence of another, 1 lesion that results from the treatment of another, 2 lesions for which circumstantial evidence suggests a connection, and finally, 2 lesions occurring together entirely by chance. Failure to recognize a second lesion after a first has been identified can result from overintense focus on the first lesion, subtlety of the second lesion, unusual situations where the second lesion involves the absence rather than presence of something, instances where the first lesion obscures the second, and disease pairs where the findings for the second are a subset of those for first. Key Messages: Detection and understanding of multiple pathological processes in a biopsy and avoiding pitfalls in their analysis requires the use of all available diagnostic modalities and thorough examination of all tissue received. Careful attention should be paid to the clinical record, but with the recognition that it may not always be entirely accurate or predictive of what will be found in the biopsy. Above all, pathologists must resist the temptation to think that their work is done when they find the first abnormality.