A rare case of PLA2R- and THSD7A-positive idiopathic membranous nephropathy

Clinicopathological and prognostic characteristics of idiopathic membranous nephropathy with dual antigen positivity

Background

Idiopathic membranous nephropathy (IMN) is the most common pathological type in adults with nephrotic syndrome. Many target antigens have been discovered. However, dual antigen-positive IMN patients are very rare, with only a few such cases being briefly described in various studies. There is no specific study on the clinicopathological and prognostic characteristics of dual antigen-positive IMN patients, and the disease characteristics of such patients remain unclear.

Methods

Immunohistochemical staining of PLA2R, THSD7A, and NELL-1 was conducted on kidney tissue samples obtained from patients diagnosed with IMN. Simultaneously, the presence of corresponding serum antibodies was determined. Patients exhibiting positivity for dual antigens were included in the study, identified either through tissue staining or serum antibody detection. We retrospectively collected their clinical, pathological, and follow-up data and measured their serum antibody levels at multiple time points. Additionally, the same type of dual antigen-positive IMN cases reported in the literature were reviewed to extract clinical, pathological, and prognostic information. We compared the data for all of the above dual antigen-positive and PLA2R single-positive IMN cases at our center.

Results

We identified 6 IMN patients with dual antigen positivity at our center, approximately 0.7% of whole MN series; the previous literature reports 43 IMN patients with dual antigen positivity, the proportion ranged from 0.2% to 2.8%. The IgG1 positivity rate in the renal tissue of the dual antigen-positive patients at our center was significantly lower than that of dual antigen-positive patients previously reported (16.7% vs. 100.0%, p=0.015), but there was no significant difference in clinical or prognostic aspects. Patients with dual antigen positivity reported at our center and in the literature were combined and compared with PLA2R single-positive IMN reported at our center. Compared with PLA2R single-positive IMN patients, dual antigen-positive IMN patients had a higher renal tissue IgG1 positivity rate (58.3% vs. 22.3%, p=0.016), and the time required to achieve remission was longer [13.5 (3.3,35.0) vs. 3.0 (1.0,8.0), p=0.052]. Overall, The changes in urine protein were consistent with the changes in serum PLA2R antibody levels in dual antigen-positive IMN patients.

Conclusions

For patients with primary membranous nephropathy who did not attain remission following prolonged treatment, multiple target antigen staining should still be actively performed, even with positivity for the PLA2R target antigen.

THSD7A as a Promising Biomarker for Membranous Nephrosis

Membranous nephropathy (MN) is an autoimmune disease of the kidney glomerulus and one of the leading causes of nephrotic syndrome. The disease exhibits heterogeneous outcomes with approximately 30% of cases progressing to end-stage renal disease. Traditionally, the standard approach of diagnosing MN involves performing a kidney biopsy. Nevertheless, kidney biopsy is an invasive procedure that poses risks for the patient including bleeding and pain, and bears greater costs for the health system. The clinical management of MN has steadily advanced owing to the identification of autoantibodies to the phospholipase A2 receptor (PLA2R) in 2009 and thrombospondin domain-containing 7A (THSD7A) in 2014 on the podocyte surface. At present, serum anti-PLA2R antibody detection and glomerular PLA2R antigen staining have been used for clinical diagnosis and prognosis, but the related detection of THSD7A has not been widely used in clinical practice. Here, we summarized the emerging knowledge regarding the roles THSD7A plays in MN and its clinical implications as diagnostic, prognostic, and therapeutic response as well as Methods for detecting serum THSD7A antibodies.

Characteristics of Anti-Contactin1 Antibody-Associated Autoimmune Nodopathies With Concomitant Membranous Nephropathy

Background

The concurrence of anti-contactin 1 (CNTN1) antibody-associated chronic inflammatory demyelinating polyneuropathy (CIDP) and membranous nephropathy (MN) has previously been reported in the literature. CIDP with autoantibodies against paranodal proteins are defined as autoimmune nodopathies (AN) in the latest research. In view of the unclear relationship between CIDP and MN, we performed a case study and literature review to investigate the clinical characteristics of anti-CNTN antibody-associated AN with MN.

Methods

We detected antibodies against NF155, NF186, CNTN1, CNTN2, CASPR1 and PLA2R in blood samples of a patient with clinically manifested MN and concomitant peripheral neuropathy via double immunofluorescence staining and conducted a quantitative measurement of anti-PLA2R IgG antibodies via enzyme-linked immunosorbent assay (ELISA). Case reports of anti-CNTN1 antibody-associated AN, anti-CNTN1 antibody-associated AN with MN, and CIDP with MN were retrieved through a literature search for a comparative analysis of clinical characteristics. The cases were grouped according to the chronological order of CIDP and MN onset for the comparison of clinical characteristics.

Results

A 57-year-old man with anti-PLA2R positive MN was admitted to the hospital due to limb numbness, weakness, and proprioceptive sensory disorder. He was diagnosed with anti-CNTN1 antibody-associated AN and recovered well after immunotherapy. Our literature search returned 22 cases of CIDP with MN that occurred before, after, or concurrently with CIDP. Good responses were achieved with early single-agent or combination immunotherapy, but eight out of the 22 patients with CIDP and concomitant MN ultimately developed different motor sequelae. Five patients had anti-CNTN1 antibody-associated AN with MN. Among these patients, males accounted for the majority of cases (male:female=4:1), the mean age at onset was late (60.2 ± 15.7 years, range 43–78 years), and 40% had acute to subacute onset. Clinical manifestations included sensory-motor neuropathy, sensory ataxia caused by proprioceptive impairment, and elevated cerebrospinal fluid protein levels.

Conclusion

The age at onset of CIDP with MN was earlier than that of anti-CNTN1 antibody-associated AN. MN may occur before, after or concurrently with CIDP. The early detection and isotyping of anti-CNTN1 and anti-PLA2R antibodies and the monitoring of isotype switching may be essential for suspected CIDP patients.

Primary Membranous Nephropathy With Enhanced Staining of Exostosin 1/Exostosin 2 in the Glomeruli: A Report of 2 Cases

Technological advances have allowed the discovery of 6 subtypes of membranous nephropathy based on target antigens: M-type phospholipase A₂ receptor (PLA₂R), thrombospondin type 1 domain-containing 7A (THSD7A), neural epidermal growth factor-like 1 protein, semaphorin 3B, exostosin 1 (EXT1), and EXT2. EXT1/EXT2 are thought to be associated with secondary (autoimmune) membranous nephropathy. Although it has been reported that PLA₂R- and THSD7A-associated membranous nephropathy have rarely been detected concomitantly, there have been no previous reports demonstrating PLA₂R- or THSD7A-associated membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. We describe 2 cases of primary membranous nephropathy with enhanced glomerular staining of EXT1/EXT2. Patient 1 was diagnosed with PLA₂R-associated primary membranous nephropathy, and patient 2 was diagnosed with THSD7A-associated primary membranous nephropathy. Both patients achieved clinical remission in response to immunosuppressive therapy. Neither patient demonstrated signs of autoimmune diseases, and antinuclear antibodies were absent in their sera. Based on these 2 cases, enhanced staining of EXT1/EXT2 in glomeruli, although rare, can be detected in primary membranous nephropathy without autoimmune diseases.