To describe an atypical initial presentation of childhood-onset granulomatosis with polyangiitis (GPA) involving suspected necrotizing myositis.
Approach:
Case: A previously healthy 16-year-old girl developed progressive calf and hip pain, severe anemia, inflammation, hemoptysis, and respiratory failure. MRI showed rim-enhancing intramuscular collections.
Diagnostic evaluation: Cultures and testing for multiple infectious, autoimmune, toxic, and other causes were negative. c-ANCA was positive at 1:160 and PR3 antibody was 4.4 (reference <0.9). Muscle biopsy confirmation was unavailable.
Treatment and follow-up: Treatment included pulse intravenous methylprednisolone, rituximab, and seven plasma-exchange sessions, followed by a steroid taper and avacopan. Rituximab maintenance was continued.
Key Findings:
The authors attributed the intramuscular collections and hip pain to GPA-associated necrotizing myositis.
The patient’s lung function stabilized after pulse methylprednisolone; she was extubated after 16 days.
Clinical remission was attained. At six months, chest CT showed largely resolved lung disease with minimal residual scarring.
The patient later returned to school, work, and sports.
Interpretation:
The report describes a 16-year-old girl diagnosed with GPA after presenting with progressive leg pain, intramuscular collections, and severe pulmonary disease. Her hip pain was attributed to GPA-associated necrotizing myositis, although muscle biopsy confirmation was unavailable.
Limitations:
Muscle biopsy confirmation of necrotizing myositis was unavailable.
This is a single case report and cannot establish prevalence or treatment effectiveness.
Conclusion:
The authors report a case of childhood-onset GPA presenting with intramuscular collections and hip pain attributed to suspected necrotizing myositis. The patient improved after immunomodulatory treatment and attained clinical remission.
