A Case of Idiopathic Multicentric Castleman Disease Developing in a Patient with a History of Biopsy Proven Membranous Nephropathy

Abstract Introduction/Objective Idiopathic multicentric Castleman disease (iMCD) is a lymphoproliferative disorder involving two or more lymph node sites. It is usually associated with systemic inflammatory symptoms and organ dysfunction related to hypercytokinemia. Renal involvement in iMCD has only been described in a limited number of studies and case reports. Of note, only one previous case report has described results from renal biopsies taken prior to the development of iMCD. Methods/Case Report Our patient is a 43 year old female who was first diagnosed with membranous nephropathy in early 2020. She had PLA2 R negative and Exostosin-2 positive disease. Age appropriate screening for malignancy was unremarkable. She had positive ANA titres and normal complement levels but did not meet criteria for SLE per rheumatology. Her proteinuria was improved and maintained on Lisinopril for 3 years. In October 2023, her proteinuria suddenly increased. Repeat renal biopsy was unchanged from the initial biopsy. This time, she also noticed acute swelling over her subpectoral region. PET-CT scan revealed multiple areas of avid lymphadenopathy on either sides of the diaphragm but the highest yield PET- avidity was in the subpectoral region. Biopsy of the right subpectoral lymph node was performed. According to the WHO Classification, 5th edition, diagnostic criteria for iMCD-NOS was met with the histological features displaying grade 3 plasmacytosis, grade 2 regressed germinal centers, follicular dendritic cell prominence, increased hyperplastic follicles and increased vascularity. Immunohistochemical staining for CD138 highlighted abundant plasma cells, CD21 highlighted follicular dendritic cell prominence. Vascular proliferation was seen by CD34 staining. Kappa and Lambda- ISH demonstrated polytypic staining pattern and HHV-8 was negative. Results (if a Case Study enter NA) NA Conclusion There is a significant clinical, histologic and immunologic overlap between iMCD, autoimmune or infectious disorders and malignancy. HHV-8 negative/iMCD is less well understood and has no specific biomarkers. It is important to follow the available clinicopathologic diagnostic criteria for early diagnosis, follow up and treatment. Timely recognition can help prevent multiple organ system dysfunction, systemic inflammatory symptoms, cytopenias and polyclonal lymphoproliferation. Although the pathophysiology maybe unclear, this case may also suggest that in patients with a previously diagnosed membranous nephropathy, iMCD may play a role in recurrence and worsening of the disease.