The clinicopathological implications of endothelial tubuloreticular inclusions found in glomeruli having histopathology of idiopathic membranous nephropathy

Abstract

The pathological recognition of secondary membranous nephropathy (MN) is sometimes difficult, especially in those showing primary idiopathic MN-like histomorphology. The ultrastructural finding of tubuloreticular inclusions (TRIs) in MN always evokes suspicion of their association with underlying diseases such as viral infections and autoimmune diseases. However, it is not clear whether some other underlying diseases are associated with TRI expression in MN. Since treatment of the underlying diseases is the primary consideration for the management of secondary MN, it is important to make out the clinical significance of TRI expression in MN. Excluding the patients fully qualified for systemic lupus erythematosus (SLE) diagnostic criteria, we recruited 36 cases having a renal biopsy featured with histopathology of primary idiopathic MN but ultrastructural appearance of TRIs in glomerular endothelial cells (GECs). We investigated their clinical and pathological profiles and focused on the potential connections with the underlying diseases and treatment outcomes. One-third of our cases showed no identifiable underlying aetiology. Other underlying disease groups included autoimmune disease (25%), hepatitis (14.7%), potential Helicobacter pylori infection (13%), diabetes (5.6%) and lymphoma (5.6%). Pathologically, patients in the autoimmune group tended to have more heterogeneous membranous deposits with frequent mesangial and subendothelial deposits. While all patients of the autoimmune group presented complement C1q in glomeruli, more than two-thirds of the patients in others groups were negative for C1q. Clinically, the patients in autoimmune and hepatitis groups were younger in age and had less remission of proteinuria following treatment, while the other groups of patients achieved partial or complete remission more frequently. The underlying diseases of our patients were consistent with the major disease categories that have been frequently linked to secondary MN. The HP group was more akin to undefined groups regarding their pathological and clinical profiles. Since the MN in the undefined group might be the only renal manifestation antedating other clinical presentations of the corresponding underlying disease, a long-term follow-up and meticulous search for aetiological factors are required to validate this assumption.