• Julie Obert, Laetitia Vercellino, Axel Van Der Gucht, Constance de Margerie-Mellon, Emmanuelle Bugnet, Sylvie Chevret, Gwenaël Lorillon, and Abdellatif Tazi.
• Université Paris Diderot, Sorbonne Paris Cité, Paris, France.
• Eur. J. Nucl. Med. Mol. Imaging. 2017 Apr 1; 44 (4): 598-610.

PurposeThe standard evaluation of multisystem Langerhans cell histiocytosis (LCH) includes a clinical evaluation, laboratory tests and a skeleton/skull X-ray survey, with chest high-resolution computed tomography (HRCT) in the case of pulmonary involvement. Preliminary reports suggest that 18F-fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) may be useful for evaluating patients with LCH.MethodsFourteen consecutive adult patients with multisystem LCH were included in this retrospective study, and were evaluated using standard procedures and 18F-FDG PET-CT. The two sets of findings were compared both at baseline and during follow-up. Serial HRCT and pulmonary function tests were used to evaluate outcome in patients with lung involvement.ResultsAt the baseline evaluation, PET-CT identified every LCH localization found with the standard evaluation (except a mild cecum infiltration). PET-CT showed additional lesions in seven patients, mostly involving bones, and differentiated inactive from active lesions. Thyroid 18F-FDG uptake was identified in three cases. No pituitary stalk 18F-FDG uptake was observed in patients with pituitary LCH. Only 3/12 (25 %) patients with pulmonary LCH displayed moderate pulmonary 18F-FDG uptake. During follow-up, variations (≥50 % of maximum standardized uptake) in bone 18F-FDG uptake intensity were correlated with disease state and response to treatment. The absence of lung 18F-FDG uptake did not preclude lung function improvement after treatment.ConclusionsExcept for cases with pulmonary and pituitary involvement, 18F-FDG PET-CT could replace the standard evaluation for staging of adult patients with multisystem LCH. Serial PET-CT scans are useful for evaluating treatment responses, particularly in cases with bone LCH involvement.

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