Abstract
BACKGROUND: Immunoglobulin G4 (IgG4)-related disease (IgG4-RD) is a systemic fibroinflammatory disorder defined by elevated serum IgG4, tissue IgG4+ plasma cell infiltration, and multi-organ involvement. Paradoxically, helminth infections may also trigger IgG4 elevation through Th2-polarized immune responses, creating diagnostic ambiguity when overlapping features occur. Critically, no studies have addressed whether IgG4-RD with helminthiasis can coexist in children or how to differentiate them when histopathology is unavailable. CASE DESCRIPTION: A 10-year-old boy with confirmed pulmonary paragonimiasis developed refractory pericardial effusion and markedly elevated IgG4 [11 g/L, 8.1× upper limit of normal (ULN)]. Despite five courses of praziquantel (75 mg/kg/day), effusions persisted for 8 weeks. Subsequent glucocorticoids (methylprednisolone 2 mg/kg/day) achieved rapid clinical resolution, though lacked histopathology IgG4-RD hallmarks. Longitudinal monitoring revealed a dynamic IgG4 decline (from 11 to 5.25 g/L) post-methylprednisolone therapy. However, residual IgG4 elevation (5.25 g/L, >3× ULN) and absent histopathological features of IgG4-RD left the diagnosis unresolved. Therapeutic monitoring revealed normalized eosinophils and imaging improvement, yet persistent IgG4 suggested potential immune dysregulation beyond parasitic clearance. CONCLUSIONS: This case highlights a critical diagnostic dilemma: IgG4 elevation in parasitic infections may mimic or coexist with IgG4-RD. The rapid glucocorticoid response argues against simple parasitic infections, yet incomplete IgG4 normalization post-treatment leaves coexistence unresolved. Clinicians must weigh these possibilities when anti-helminthic therapy fails, particularly when histopathology is absent. Prospective studies should define pediatric-specific IgG4 thresholds to disentangle infection from autoimmunity.