In search of a disease.

A 10-year-old child presented with right eyelid swelling and a palpable orbital mass. Diagnostic evaluation with the aid of excisional biopsy revealed a pseudoencapsulated mass associated with high levels of serum perinuclear antineutrophil cytoplasmic antibodies. Family history of rheumatic diseases, response to treatment with corticosteroids and immunosuppressant drugs, and clinical and histopathologic features suggested an orbital autoimmune response in which perinuclear antineutrophil cytoplasmic antibodies were detected, and a diagnosis of probable IgG4-related disease was made.