ANCA-negative microscopic polyangiitis with neuromuscular involvement: When pathology could make the difference

Area of Science:

• Nephrology
• Rheumatology
• Neurology

Background:

• Microscopic polyangiitis (MPA) is a pauci-immune small vessel vasculitis often associated with antineutrophil cytoplasmic autoantibodies (ANCA).
• MPA typically presents with diverse organ manifestations, including renal and pulmonary involvement.

Observation:

• A 74-year-old Asian man presented with rapid onset lower limb weakness, renal, and pulmonary dysfunction.
• Antineutrophil cytoplasmic autoantibody (ANCA) levels were borderline throughout the disease course.
• Electrophysiological studies indicated neuromuscular involvement, and biopsies confirmed small vessel vasculitis.

Findings:

• The patient's condition improved significantly after initiating targeted immunosuppressive combination therapy.
• This case highlights a presentation of MPA with neuromuscular symptoms and borderline ANCA levels.

Implications:

• Microscopic polyangiitis should be considered in the differential diagnosis of acute/subacute muscle weakness, particularly when accompanied by organ dysfunction.
• The absence of definitive ANCA detection should not exclude MPA in patients with suggestive clinical and pathological findings.
• This underscores the importance of a comprehensive diagnostic approach for multi-organ diseases like MPA.