Unique microstructures and podocytic infolding in glomerular basement membrane associated with collagen diseases: a report of three cases

Podocyte Infolding Glomerulopathy: A Special Morphology of Podocyte Injury Caused by Heterogeneous Diseases

Introduction

Podocyte infolding glomerulopathy (PIG) is a newly recognized rare glomerular injury. The clinical significance and mechanism of this injury pattern remains unclear.

Methods

We conducted a retrospective study of renal biopsies from January 2018 to December 2020 in Kingmed Diagnostics. The renal biopsy features and clinical data were reviewed. Laser scanning microdissection and mass spectrometry (LMD/MS) was conducted to analyze the potential mechanism.

Results

A total of 116 (0.092%) out of 126,086 biopsies were diagnosed as PIG during the period. Of these, 89 (76.7%) cases were found to have PIG coexisting with immune-complex associated glomerulonephritis (IC-PIG) whereas 27 (23.3%) were identified as isolated PIG without immunoglobulin or complement deposition. Systemic lupus erythematosus (SLE), especially with membranous lupus nephritis (LN), was diagnosed in most (70.8%) IC-PIG cases. Of the isolated PIG cases, 51.9% had no known underlying conditions; however, a relatively high positive rate (42.1%) of antinuclear antibody (ANA) was detected. Nearly half (47.5%) of the patients presented with nephrotic syndrome (NS). PIG grade was associated with proteinuria in isolated PIG (P = 0.035). LMD/MS revealed dysregulated cytoskeletal protein α-actinin4 (ACTN4) and tubulin beta-4 chain in PIG compared with normal donor kidney and minimal change disease (MCD). The displacement of ACTN4 into the glomerular basement membrane (GBM) was confirmed by the confocal microscope.

Conclusion

PIG is a rare podocyte injury that can exist alone without underlying disease or be concurrent with various diseases, especially SLE. Podocyte cytoskeletal protein ACTN4 and tubulin beta-4 chain were dysregulated, which may be involved in the mechanism of PIG.

Podocyte infolding glomerulopathy after 25 years of clinical remission of lupus nephritis in a patient with systemic lupus erythematosus: A case report and review of literature

Podocyte infolding glomerulopathy (PIG) is a rare pathological finding that has gained more recognition recently. Most of the reported cases have been associated with connective tissue diseases especially systemic lupus erythematosus (SLE). Here we report the first case of Infolding Glomerulopathy associated with SLE in the Middle East.

Subepithelial deposits with microspherular structures in membranous glomerulonephritis

Rare cases of membranous glomerulopathy (MGN) with subepithelial deposits consisting of microspherular structures identified by electron microscopy have been described in the literature as either MGN with spherules or podocyte infolding glomerulopathy (PIG). The paucity of available studies shows a strong association with underlying autoimmune disease. To further understand the significance of subepithelial microspherular deposits, we retrospectively identified native kidney biopsies from 10 patients diagnosed as MGN with subepithelial microspherular structures identified by ultrastructural examination at the University of Rochester Medical Center (URMC) during an 11-year period. The majority were Caucasian (80%) with a mean age of 51.3 (±12.9) years. 50% had an autoimmune disorder, of which 80% were SLE. Two SLE cases had concomitant rheumatoid arthritis and Sjogren's syndrome. One additional case had antiphospholipid syndrome and showed lupus-like features on biopsy. 40% were idiopathic and negative for PLA2R, NELL1, and THSD7A. MGN with subepithelial microspherular structures is frequently associated with an underlying autoimmune disease. The majority are negative for markers of primary MGN (PLA2R, THSD7A, and NELL1) and show features suggestive of secondary MGN.

Podocyte Infolding Glomerulopathy, First Case Report From North America

Rationale

Podocyte infolding glomerulopathy (PIG) is a newly described condition with only 37 cases reported worldwide. Due to its rarity, the pathogenesis and evolution of this disease is unclear. This case report contributes to our collective knowledge about the clinical and histological progression of this disease.

Presenting concerns of the patient

Over the course of a year, a 52-year-old Malaysian woman with no known prior medical history developed progressively worsening edema and other findings consistent with nephrotic syndrome.

Diagnosis

Unlike most patients with PIG, this patient did not have any autoimmune disease. She was Hepatitis B core antibody positive with a Hepatitis B surface antibody >1000, suggesting prior Hepatitis B infection with immunity. A renal biopsy was performed which was consistent with PIG. A second renal biopsy was done 2 years later which again showed characteristic findings of PIG with worsened podocyte effacement but no interval change in chronicity.

Interventions

The patient was treated with blood pressure control and renin-angiotensin-aldosterone system (RAAS) blockade with irbesartan and spironolactone. She was also treated with prednisone at 1 mg/kg for 2 months followed by a taper for a total of 7 months of prednisone treatment.

Outcomes

The patient had a partial response to a course of prednisone. However, since stopping steroids, her proteinuria and renal function has been gradually worsening.

Teaching points

PIG is mostly found in patients of East Asian descent. It presents as proteinuria and is often associated with autoimmune disease but can be idiopathic. It is characterized on renal biopsy by infolding or protrusion of podocyte cytoplasm into glomerular basement membrane, as well as intramembranous cytoplasmic microspherules or microtubules. Atypical membranous nephropathy should be ruled out prior to diagnosis. Unlike membranous nephropathy, PIG usually responds at least partially to steroid monotherapy. To our knowledge, this is the first reported case of PIG from North America. Furthermore, it is the first case of PIG with repeat biopsy showing interval worsening of PIG rather than either resolution of PIG or transformation of PIG to a different diagnosis.

Podocyte infolding glomerulopathy with undifferentiated connective tissue disease: a case report

Podocyte infolding glomerulopathy (PIG) is a special type of glomerular disease that has been proposed in recent years and has attracted considerable attention. PIG is characterized by the formation of microspheres and microtubules in thickened glomerular basement membrane (GBM) on electron microscopy (EM), which is recognized as podocyte cytoplasmic infolding to the GBM. However, to date, only a few cases of PIG have been reported. Herein, we report a case of a 33-year-old female with PIG with undifferentiated connective tissue disease (UCTD) in China and review the literature.

Podocyte infolding glomerulopathy; report of the first case in Latin America and review of the literature

BACKGROUND

Podocyte infolding glomerulopathy (PIG) is a condition of uncertain origin, frequently associated with autoimmune diseases. Its specific treatment and clinical course are unknown. It is characterised by thickening of the capillary walls due to the presence of non-argyrophilic intramembranous bubbles similar to those found in membranous glomerulopathy, but without electron-dense deposits of immune complexes in the ultrastructure, where translucent microspheres generated by invagination of the podocyte cytoplasm into the basement membranes are observed.

OBJECTIVES

Generally reported in young females patients. To date, few cases in Asian patients have been reported. Our case is the first to be reported in a Latin American Caucasian patient.

METHODS

A 38-year-old woman with SLE. In 2014 she presented with nephrotic syndrome empirically treated with corticosteroids (CO) and intravenous cyclophosphamide with good response. She had a relapse in April 2015 with normal renal function and no extrarenal lupus activity, so she was referred to our hospital to be biopsied.

RESULTS

The biopsy reported focal segmental glomerular sclerosis without deposits of immune complexes in the immunofluorescence. However, methenamine silver staining revealed clear spaces in the capillary walls accompanied by marked podocyte alterations. On electron microscope study, numerous aggregates of microvesicular and cylindrical ultrastructures bound to the membranes were observed, without evidence of dense deposits, and diffuse effacement of pedicel foot processes, confirming the suspected diagnosis.

CONCLUSIONS

This is the first reported case of what can be considered a new pathological glomerular entity in a Latin American Caucasian patient, whose clinical course and therapy are still unknown.

Podocytic infolding glomerulopathy: two new cases with connective tissue disease and literature review

Podocytic infolding glomerulopathy (PIG) is a newly proposed disease entity, and only 29 cases have been reported worldwide so far, characterized by microspheres or microtubular structures or both associated with podocytic infolding into the glomerular basement membrane (GBM) on electron microscopy. We present two new cases of PIG with connective tissue disease (CTD), one with primary Sjögren's syndrome and the other with systemic lupus erythematosus (SLE), and make a systemic review of the literature. In the entire 31 patients of PIG, 24 (77.42%) were women and seven (22.58%) were men, with an average age of 41.2 ± 15.2 (ranging from 14 to 79) years old. Almost two-thirds of patients (67.74%) were diagnosed with CTD, in which 76.19% were SLE. All patients presented with proteinuria and six (19.35%) patients were accompanied with hematuria. Serum creatinine was elevated in six (19.35%) patients. Pathological findings of all patients were consistent with PIG characteristics, and four patients with repeated renal biopsies further provided profound insights.