FDG PET‐CT in pediatric Langerhans cell histiocytosis

Objective Langerhans cell histiocytosis (LCH) in pediatric patients presents with single‐system or multisystem disease. Accurate staging is essential for selecting the most appropriate therapy ranging from local surgery to chemotherapy. Methods A retrospective review was undertaken of reported fludeoxyglucose (FDG) positron emission tomography ‐ computed tomography (PET‐CT) scans performed in children with LCH from June 2006 to February 2017. Findings were compared with a reference standard of biopsy or informed clinical follow‐up. Results One hundred nine scans were performed in 33 patients (age 7 weeks to 18 years). Nineteen patients had single‐system, bone unifocal disease; seven patients had single‐system, bone multifocal disease; four patients had single‐system, skin unifocal disease; two patients had multisystem disease; and one patient had single‐system, lymph node disease. Twenty‐six scans were performed to stage biopsy‐proven LCH, and 83 scans were performed during follow‐up to assess treatment response or recurrence after therapy completion. At staging, FDG PET‐CT detected all sites of biopsy‐proven LCH (except where bone unifocal disease had been resected). There was one false‐positive thymic finding that resolved without therapy. The per‐patient false‐positive rate of FDG PET‐CT at staging was 4% (1/26). During follow‐up, five LCH recurrences and one case of progressive disease on therapy occurred, all positive on FDG PET‐CT. During follow‐up two patients had FDG PET‐CT scans with false‐positive findings and one patient with a magnetic resonance imaging false‐positive finding. The per‐scan false‐positive rate of FDG PET‐CT during follow‐up was 2% (2/83). Conclusions FDG PET‐CT is highly sensitive for the staging and follow‐up of pediatric patients with LCH, and has a very low false‐positive rate.