Abnormal fluorodeoxyglucose PET in pulmonary Langerhans cell histiocytosis

Background: Pulmonary Langerhans cell histiocytosis (PLCH) is an inflammatory lung disease strongly associated with cigarette smoking and an increased risk of malignant neoplasms. Although the chest CT scan characteristics of PLCH are well recognized, the PET scan characteristics of adults with PLCH are unknown. Methods: We identified 11 patients with PLCH who underwent PET scanning over a 6-year period from July 2001 to June 2007. The presenting clinicoradiologic features including PET scan and chest CT scan findings were analyzed. Results: Five of 11 patients had positive PET scan findings. Of the five PET scan-positive patients, 4 (80%) were women, 4 (80%) were current smokers, and the median age was 45 years (age range, 31 to 52 years). PET scan-positive findings were more likely to be present if the scan was performed early in the clinical course. Three PET scan-positive patients (60%) had multiorgan involvement. PET scan-positive patients had predominantly nodular inflammatory lung disease (> 100 nodules) with most nodules measuring < 8 mm, whereas all PET scan-negative patients had predominantly cystic lung disease with fewer nodules (< 25 nodules). Notable abnormal PET scan findings included foci of increased uptake in nodular lung lesions, thick-walled cysts, bone, and liver lesions. The mean maximum standardized uptake value of the PET scan-positive lesions ranged from 2.0 to 18.2. Conclusions: PLCH may be associated with abnormal thoracic and extrathoracic PET scan results. Patients with nodular disease seen on chest CT scans appear more likely to have abnormal PET scan findings. Our results suggest that PET scan imaging cannot reliably distinguish between the benign inflammatory nodular lesions of PLCH and malignant lesions.