Subacute parkinsonism associated with proteinuria, hematuria, and PR3-ANCA positivity: a diagnostic challenge

BACKGROUND: Secondary causes of parkinsonism, such as tumors and autoimmune conditions, are rare. Cases of parkinsonism owing to antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis of the central nervous system (CNS) or lymphoma are scarce and often difficult to differentiate using neuroimaging. Herein, we present a rare and challenging case of secondary parkinsonism that showed subacute progression with ANCA positivity. CASE PRESENTATION: A 69-year-old healthy woman presented with subacute progressive parkinsonism. The patient showed proteinuria, hematuria, and positive proteinase 3-specific ANCA (46.0 U/mL; normal range < 2 U/mL). Brain MRI revealed cerebral ischemic lesion and extensive white matter hyperintensities on T2-FLAIR indicative of CNS-ANCA vasculitis of the CNS. Although methylprednisolone pulse therapy improved her condition temporarily, it deteriorated 2 weeks later. Renal biopsy confirmed IgA nephropathy, and subsequent brain biopsy revealed diffuse large B-cell lymphoma (DLBCL). Despite the initiation of chemotherapy, her condition deteriorated further, and the patient died 1 month later. CONCLUSION: We present a case of lymphoma with proteinuria, hematuria, positive ANCA, and brain MRI findings mimicking ANCA-associated vasculitis. DLBCL and IgA nephropathy can coexist, and differentiating between DLBCL and ANCA-associated vasculitis from MRI images can be challenging in some rare cases. This study highlights the importance of tissue diagnosis even when CNS vasculitis is suspected.