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.