Microscopic polyangiitis: Atypical presentation with extensive small bowel necrosis, diffuse alveolar hemorrhage, and renal failure

Area of Science:

• Rheumatology
• Gastroenterology
• Nephrology

Background:

• Microscopic polyangiitis (MPA) is a rare systemic vasculitis often associated with myeloperoxidase (MPO) and perinuclear antineutrophil cytoplasmic (p-ANCA) antibodies.
• Typically, MPA affects the lungs and kidneys, leading to conditions like diffuse alveolar hemorrhage and acute kidney injury.

Observation:

• This report details an unusual MPA case presenting with severe mesenteric ischemia, alongside diffuse alveolar hemorrhage and acute renal failure.
• The patient's initial symptoms of severe abdominal pain and elevated pancreatic enzymes led to a misdiagnosis of acute pancreatitis.

Findings:

• Diagnostic investigations confirmed a severe exacerbation of previously diagnosed microscopic polyangiitis as the underlying cause.
• The patient developed acute kidney injury requiring dialysis and diffuse alveolar hemorrhage necessitating intubation.
• Mesenteric ischemia and bowel necrosis ensued, requiring emergent laparotomy and extensive small bowel resection.

Implications:

• Physicians must consider microscopic polyangiitis in the differential diagnosis for severe abdominal symptoms, even when pancreatitis is suspected.
• Rarely, MPA can manifest with significant gastrointestinal and mesenteric vascular involvement.
• Aggressive treatment for severe MPA exacerbations includes high-dose corticosteroids, immunosuppressants (rituximab or cyclophosphamide), and plasma exchange.