Podocyte Infolding Glomerulopathy (PIG) in a Patient With Undifferentiated Connective Tissue Disease: A Case Report

Podocyte Infolding Glomerulopathy Masquerading as Membranous Nephropathy - A Shared Pathogenesis?

Podocyte infolding glomerulopathy (PIG) is a rare pathological entity, diagnosed by electron microscopic demonstration of diffuse infolding of the podocytes into the glomerular basement membranes. We report the first case from United Kingdom exhibiting typical ultrastructural features of PIG in a male with Type II diabetes mellitus, hypertension and common variable immune deficiency. Renal biopsy revealed phospholipase A2 receptor (PLA2R) immunostain positive membranous nephropathy (MN) but no serum PLA2R antibodies. Diffuse infolding of the podocytes into the glomerular basement membranes along with pathognomonic microspherular and microtubular intra basement membrane clusters distributed diffusely and globally were noted on electron microscopy, diagnostic of PIG. We postulate a shared pathomechanistic link between PIG and MN, highlighting the overlapping features of both conditions.

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.

Integrated Chinese and Western medicine in the treatment of a patient with podocyte infolding glomerulopathy: A case report

BACKGROUND

Podocyte infolding glomerulopathy (PIG) is a newly described and rare glomerular disease. To date, only approximately 40 cases have been reported globally.

CASE SUMMARY

A 26-year-old female patient presented to our hospital with a complaint of intermittent edema of both lower limbs over the past 2 years. The patient was diagnosed with PIG. She was prescribed corticosteroid therapy in other hospitals during the initial stage, to which she had responded poorly and had developed femoral head necrosis. Therefore, we administered immunosuppressants, renin-angiotensin system inhibitors, combined with traditional Chinese medicine. The patient was followed for 1 year, during which her clinical condition improved.

CONCLUSION

Integrated Chinese and Western medicine may be effective for PIG treatment, which requires active intervention to improve prognosis.

Podocyte Infolding Glomerulopathy: A Case Series Report and Literature Review

BACKGROUND

Podocyte infolding glomerulopathy (PIG) is a peculiar and very rare manifestation in renal pathology. Its underlying pathogenesis mechanism and clinical characteristics remain unclear due to sparse reports.

OBJECTIVE

To further elucidate the clinical profile of PIG by carefully reporting our four cases and a comprehensive review of cases in the literature.

METHODS

This study retrospectively reviewed four cases of PIG from 2010 to 2022 in our centre. Clinical and pathological profiles were reported. PIG cases in the literature were searched in the MEDLINE database and analysed together with our cases.

RESULTS

Four cases of PIG identified from our centre and 40 cases from the current literature were reported. The pooled analysis of these 44 cases indicated 79.5% (35/44) were females, 93.2% (41/44) were East Asians, and 63.6% (28/44) were reported in Japan. The average age was 42.0 ± 12.5 years old. The average amount of proteinuria at the time of renal biopsy was 3.06 ± 3.2 g/day. The most reported comorbidities were connective tissue diseases, mainly systemic lupus erythematosus, and 20.5% (9/44) of the cases did not have any contaminant disease. Most of the cases (81.8%, 36/44) had been treated with immunosuppressants, of which a combination of corticosteroids and one other type of immunosuppressant was most commonly reported. In addition, 45.4% (20/44) and 34.1% (15/44) of the cases had achieved complete response and partial response, respectively, after treatment. Whole exosome sequencing indicated mutations in the INF2 gene.

CONCLUSIONS

PIG is a rare condition and seen in relatively younger populations, often associated with connective tissue diseases clinically and one or two other glomerulopathies histologically. The outcomes following immunosuppressive treatment are relatively good. Mutations in INF2 might be involved in the development of PIG; however, the implications of these results need to be investigated.

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.

Podocytic Infolding Glomerulopathy in a Patient with Phospholipase A2 Receptor-Positive Membranous Nephropathy and Review of the Literature

Podocytic infolding glomerulopathy (PIG) is a rare diagnosis based on characteristic histopathologic findings on renal biopsy and was proposed as a new entity about a decade ago. It is a type of podocytic injury, characterized by invagination of the podocyte cell membrane (cytoplasmic projections from podocytes) into the glomerular basement membrane. The presence of microspheres and/or microtubules on electron microscopy is the characteristic finding. PIG is most often associated with autoimmune conditions like systemic lupus erythematosus. We report pathologic findings typical of PIG in a patient with phospholipase A2 receptor antibody-positive membranous nephropathy. She was treated with rituximab and responded well with decrease in proteinuria to the sub-nephrotic range.

Podocytic infolding in Schimke immuno-osseous dysplasia with novel SMARCAL1 mutations: a case report

Background

Schimke immuno-osseous dysplasia (SIOD) is a rare autosomal recessive disorder characterized by spondyloepiphyseal dysplasia, progressive renal insufficiency and defective cellular immunity. Podocytic infolding glomerulopathy (PIG) is a newly proposed disease entity characterized by microspheres or microtubular structures associated with podocytes infolding into the glomerular basement membrane (GBM) on electron microscopy (EM).

Case presentation

A 4-year-old boy was admitted to our ward due to proteinuria and edema lasting 1 month. He had a short trunk and demonstrated subtle dysmorphology, with a triangular shape, a broad nasal bridge and a bulbous nasal tip. The laboratory findings were as follows: lymphocytes, 0.5 × 10⁹/L; urine protein, 3.67 g/d; albumin, 9.8 g/L; and cholesterol, 11.72 mmol/L. Skeletal X rays showed small iliac wings, small ossification centers of the capital femoral epiphyses, shallow dysplastic acetabular fossae and mildly flattened vertebrae. The specimen for light microscopy (LM) suggested focal segmental glomerulosclerosis (FSGS). EM revealed a focal thickness of the GBM with some cytoplasmic processes of podocyte infolding into the GBM. Gene sequencing showed novel compound heterozygous mutations in the SMARCAL1 gene (c.2141 + 5G > A; c.2528 + 1G > A) that were inherited from his parents. Finally, we established the diagnosis of SIOD and treated him with diuretics and angiotensin-converting enzyme inhibitors (ACEIs).

Conclusion

The pathogenic mechanism of PIG has not been clarified. Further studies are required to understand whether gene mutations, especially those related to podocytes, contribute to the pathogenesis of podocytic infolding.

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.

Case report: a peculiar glomerulopathy in a patient suffering from nephrotic syndrome

Background

Podocyte infolding glomerulopathy (PIG) is a rare histopathologic finding with global infolding of the podocytes into the glomerular basement membrane (GBM), accompanied by microstructures underneath. Described in 2002 for the first time, PIG was proposed as a new pathological entity in 2008 based on the largest case series so far. Yet all of the described cases derive from Asian countries. We report a case from Germany fulfilling the diagnostic criteria of PIG. Considering the scarcity of data on this entity especially in Western countries, collecting cases like ours and multicentric meta-analyses will be crucial to obtain a better understanding of PIG, its causes, clinical course and potential treatment options.

Case presentation

A 56-year-old Caucasian woman with a history of rheumatoid arthritis (RA), no other comorbidities and no known renal disease was admitted to the hospital with acute kidney injury (AKI) and nephrotic syndrome. Physical examination was unremarkable except for anasarca. Renal ultrasound revealed no abnormalities. Laboratory and urine analyses were consistent with the nephrotic syndrome and renal failure. Serological studies regarding ANA, ANCA, anti-PLA2R autoantibodies, complement, virus infections, immunofixation and quantitative light chain analysis were unremarkable. A renal biopsy was performed. Light microscopic examination showed flattened tubular epithelium consistent with acute tubular damage, no infiltrates and unremarkable glomeruli except diffuse and global holes in the GBM (Fig. 1a) and negative staining for immunoglobulin heavy-chains, light-chains and complement split products. Electron microscopy revealed a rare correlate for these holes: global peculiar infolding of podocyte cytoplasm into the GBM. Most of these infoldings were accompanied by condensation of the GBM underneath. No such condensation or electron dense deposits were found without these infoldings or outside the GBM.

Conclusion

Here we report the first case of PIG outside of Asia. Since there are only few reports about this specific finding, we feel there is a need to share information in an attempt to accumulate knowledge about this possible new entity and potential treatment options.

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.

Acquired renal glucosuria in an undifferentiated connective tissue disease patient with a SLC5A2 heterozygous mutation: A case report

INTRODUCTION

Renal glucosuria is a renal tubular disorder caused by genetic conditions, drugs, and poisons. Mutations in the SLC5A2 gene are recently found to be responsible for the inherited renal glucosuria, while undifferentiated connective tissue disease (UCTD) was not considered pathogenic for renal glucosuria. Here, we present a case of acquired renal glucosuria in a UCTD patient.

PATIENT CONCERNS

A 30-year-old woman was seen in the outpatient clinic for complaints of frequent urination and dysuria. Laboratory tests showed a urinary tract infection (UTI) and persistent renal glucosuria. After antibiotic treatment, the UTI symptoms were relieved, but the renal glucosuria remained.

DIAGNOSIS

Laboratory tests ruled out renal tubular acidosis and diabetes mellitus. Genetic analysis showed a heterozygous mutations in the SLC5A2 gene. Meanwhile, immunological tests showed a high antinuclear antibody titer (1:160) and an elevated anti-Rho/SSA antibody level. Schirmer test, tear breakup time, and lip biopsy results were all negative. The patient did not meet the criteria for any known connective diseases. Therefore, she was diagnosed with UCTD.

INTERVENTIONS

The patient was started with the treatment of Hydroxychloroquine.

OUTCOMES

Hydroxychloroquine treatment resolved the renal glucosuria. The patient's follow- up urinalysis showed no glucosuria at all.

LESSONS

This is the first case report to demonstrate that UCTD may induce renal glucosuria in a patient with a heterozygous mutation in SLC5A2. This case suggests that during the process of diagnosing renal glucosuria, in addition to familial renal glucosuria (FRG), autoimmune diseases, though rare, should also be taken into consideration.