Purpose or Case Report: Background: Langerhans cell histiocytosis (LCH) is common in adult smokers but exceedingly rare in children with very few cases reported in the literature of children <12 years who had been reported as having isolated pulmonary LCH.

Case Report: 4-year-old unvaccinated Amish boy, otherwise healthy with no significant past medical history who presented with acute respiratory distress, found to have recurrent bilateral pneumothoraces status post bilateral chest tubes placement.
Methods & Materials:
Results: Imaging findings:
CT chest demonstrated diffuse cystic changes throughout both lungs with replacement of much of lung parenchyma. All lungsegments are affected with cysts varying in size from 3-4 cm to sub-centimeter. Given the appearance, end stage hypersensitivity pneumonitis/usual interstitial pneumonia was suggested as the most likely diagnosis. Post infectious fibrosis, LCH and pneumocystis pneumonia were included in the differential diagnosis.

Pathology: Patient underwent bronchoscopy with bronchoalveolar lavage. The cytology showed no evidence of viral inclusions or fungal forms. No definitive evidence of LCHwas found with negative iron stain. Patient eventually underwent right upper lobe wedge lung biopsy which showed fibrosis and an infiltrate composed of histiocytes with clefted nuclei, admixed with eosinophils and neutrophils. Histiocytes stain was positive for CD1a, langerin and S100 and negative for ALK and BRAF V600E consistent with LCH.

Follow up:
Patient underwent treatment with Vinblastine and prednisone for 6 weeks as per LCH III protocol, however due to recurrent pneumothoraces, treatment with Cladribine as per LCH 98S protocol treatment regimen was initiated. Patient currently undergoing evaluation with Pediatric surgery and cardiothoracicsurgery for possible pleurodesis and lung transplant.
Conclusions: LCH is common in adult smokers but very rare in children with very few cases reported in the literature. In young children with characteristics clinical features and imaging findings, LCH should be part of differential diagnosis.