Coexistence of Microscopic Polyangiitis, Systemic Lupus Erythematosus, and Transthyretin Amyloidosis in an Elderly Japanese Patient With Splenic Marginal Zone Lymphoma: An Autopsy Case Report.

Marginal zone lymphoma (MZL) is a rare low-grade B-cell lymphoma characterized by its heterogeneous nature and association with chronic antigenic stimulation from infectious agents or autoimmune diseases. Both anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis and systemic lupus erythematosus (SLE) are rarely associated with hematologic malignancies, including non-Hodgkin lymphoma. We herein report an 86-year-old man with splenic MZL (SMZL) in whom autopsy revealed the coexistence of microscopic polyangiitis (MPA), SLE, and transthyretin amyloidosis (ATTR). The patient was admitted for rapidly progressive renal dysfunction (serum creatinine (Cr) from 2.04 to 6.77 mg/dL over two months) with general fatigue and loss of appetite. One year previously, SMZL had been diagnosed based on bone marrow biopsy and clinical features. At that time, the patient had renal dysfunction (Cr, 1.77 mg/dL) due to nephrosclerosis. The treatment for SMZL was postponed due to the advanced age and stable condition. On admission, MPA was suspected based on rapidly progressive glomerulonephritis, mononeuritis multiplex, and myeloperoxidase (MPO)-ANCA positivity. Hemodialysis and glucocorticoids improved serum C-reactive protein and MPO-ANCA levels after three weeks, but anuria persisted, and the patient remained dialysis-dependent. Aspiration pneumonia temporarily improved with ceftriaxone sodium hydrate; however, the patient died of sudden deterioration of oxygenation on the 49th hospital day. An autopsy revealed crescentic nephritis complicated by lupus nephritis and ATTR in the lungs and heart. The direct cause of death was cardiac and respiratory failure due to ATTR. This case highlights the potential pathophysiological interplay of multiple immune-mediated and neoplastic conditions in elderly patients, underscoring the importance for clinicians to recognize that patients with SMZL may have coexisting autoimmune diseases such as MPA and SLE. In particular, in elderly patients, the possibility of occult ATTR should also be considered.