Anti-Neutrophil Cytoplasmic Antibody (ANCA)-Associated Fasciitis Mimicking Pseudogout in an Older Patient: A Diagnostic Challenge and Treatment Approach.

ANCA-associated fasciitis is a rare manifestation of ANCA-associated vasculitis (AAV) that can mimic other conditions, such as pseudogout, especially in elderly patients. We present the case of a 93-year-old woman who initially developed polyarthralgia, muscle pain, and difficulty walking, symptoms suggestive of pseudogout. However, after further investigation, including elevated myeloperoxidase (MPO)-ANCA levels and MRI findings, she was diagnosed with ANCA-associated fasciitis. Treatment with high-dose prednisolone and rituximab led to significant clinical improvement. This case highlights the diagnostic challenges of ANCA-associated fasciitis and emphasizes the importance of a comprehensive approach for early diagnosis and management to prevent functional decline.