Dermatomyositis and microscopic polyangiitis overlap: a case-based review

Area of Science:

• Rheumatology
• Immunology
• Internal Medicine

Background:

• Idiopathic inflammatory myopathies (IIM) are rare autoimmune disorders affecting muscles, with potential for other organ involvement and increased malignancy risk.
• Antineutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV) involve small- to medium-sized vessels, commonly affecting kidneys and lungs.
• Overlap syndromes between IIM and AAV are uncommon but present a diagnostic and therapeutic challenge.

Purpose of the Study:

• To describe two novel cases of dermatomyositis (DM)-microscopic polyangiitis (MPA) overlap.
• To review the existing literature on IIM-AAV overlap syndromes.
• To characterize the clinical presentation, management, and outcomes of patients with IIM-AAV overlap.

Main Methods:

• Case report of two patients with DM-MPA overlap, detailing their clinical presentation, treatment, and follow-up.
• Systematic literature review of case reports and series involving IIM-AAV overlap.
• Analysis of aggregated data from identified studies, focusing on demographics, IIM and AAV subtypes, organ involvement, serological markers, treatment, and outcomes.

Main Results:

• The two reported patients with DM-MPA overlap showed significant improvement with corticosteroids and cyclophosphamide.
• Literature review identified 15 patients with IIM-AAV overlap, predominantly female, with dermatomyositis and microscopic polyangiitis being the most common subtypes.
• Renal involvement (pauci-immune crescentic glomerulonephritis) was frequent, followed by pulmonary involvement; MPO-ANCA positivity was common (12/15).

Conclusions:

• IIM-AAV overlap is a rare but potentially severe condition requiring early recognition and individualized immunosuppressive therapy.
• Treatment with corticosteroids and immunosuppressants can lead to favorable outcomes, including remission of organ dysfunction.
• Further multicenter studies are needed to elucidate the epidemiology, clinical spectrum, optimal management, and pathogenic mechanisms of IIM-AAV overlap.