Which type of Anti-Neutrophil Cytoplasmic Antibodies (ANCA) vasculitis, P-ANCA (Perinuclear-ANCA) or C-ANCA (Cytoplasmic-ANCA), is more common in children?

P-ANCA (MPO-ANCA) Vasculitis is More Common in Children

In pediatric ANCA-associated vasculitis, P-ANCA (perinuclear ANCA) associated with microscopic polyangiitis (MPA) is significantly more common than C-ANCA (cytoplasmic ANCA) associated with granulomatosis with polyangiitis (GPA).

Epidemiology of Pediatric ANCA Vasculitis

Recent evidence demonstrates a clear predominance of P-ANCA/MPO-ANCA vasculitis in the pediatric population:

• A 2023 study from Central California found that among pediatric ANCA vasculitis cases, MPA (typically associated with P-ANCA/MPO-ANCA) was more common than GPA (typically associated with C-ANCA/PR3-ANCA), with 12 MPA cases versus 9 GPA cases 1

• A 2019 Japanese multicenter study of childhood-onset AAV showed an even stronger predominance, with 78% of cases being MPA (predominantly P-ANCA/MPO-ANCA) compared to only 18% GPA (predominantly C-ANCA/PR3-ANCA) 2

• The 2021 study on pulmonary manifestations in pediatric ANCA vasculitis also confirmed this pattern, with MPA being more common than GPA 3

ANCA Patterns and Disease Associations

Understanding the antibody patterns helps in diagnosis and management:

• P-ANCA typically targets myeloperoxidase (MPO-ANCA) and is most commonly associated with microscopic polyangiitis (MPA) 4

• C-ANCA typically targets proteinase 3 (PR3-ANCA) and is most commonly associated with granulomatosis with polyangiitis (GPA) 4

• In adults, GPA is more common than MPA in European populations, but in children, this pattern is reversed 4, 1, 2

Clinical Implications of ANCA Pattern in Children

The predominance of P-ANCA/MPO-ANCA in pediatric vasculitis has important clinical implications:

• Children with MPA (P-ANCA/MPO-ANCA) tend to have more severe renal disease, with higher rates of ICU admission and dialysis requirement 1

• MPA patients show more frequent pulmonary hemorrhage, which can be life-threatening 3, 1

• GPA patients (C-ANCA/PR3-ANCA) more frequently present with ENT involvement (89%) 1

Demographic and Ethnic Considerations

Interesting demographic patterns have been observed:

• MPA (P-ANCA/MPO-ANCA) shows female predominance in pediatric populations 1, 2

• Ethnic variations exist: Hispanic children demonstrate frequent MPO-ANCA positivity, while white patients more commonly have PR3-ANCA positivity 1

Diagnostic Approach

When evaluating a child with suspected ANCA vasculitis:

1. Test for both P-ANCA/MPO-ANCA and C-ANCA/PR3-ANCA
2. Recognize that P-ANCA/MPO-ANCA is more likely in pediatric patients
3. Look for renal involvement (present in nearly all MPA cases)
4. Assess for pulmonary manifestations, which are common in both types but more severe in MPA
5. Evaluate for ENT involvement, which is more characteristic of GPA

Treatment Considerations

While treatment approaches are similar for both types of ANCA vasculitis, some differences exist:

• MPA patients may require more aggressive initial management due to higher rates of severe disease 1
• Rituximab is used more frequently in pediatric MPA cases 1
• GPA patients more commonly receive cyclophosphamide with steroids 1

Prognosis and Monitoring

Long-term outcomes differ between the two types:

• Recurrence rates are higher in GPA (C-ANCA) patients 2
• End-stage renal disease is more common in MPA (P-ANCA) patients 2
• Regular monitoring for disease activity is essential, particularly in GPA patients who have higher relapse rates 5

In summary, while both P-ANCA and C-ANCA associated vasculitides occur in children, P-ANCA (MPO-ANCA) associated microscopic polyangiitis is clearly more common in the pediatric population, with distinct clinical features and treatment considerations compared to adult populations.