18F-FDG PET in neurodegenerative Langerhans cell histiocytosis : results and potential interest for an early diagnosis of the disease.

INTRODUCTION: The so called "neurodegenerative Langerhans cell histiocytosis" (ND-LCH) is a rare and severe complication of LCH presenting as a progressive cerebellar ataxia associated with pyramidal tract signs, and cognitive impairment. MRI is the gold standard to investigate CNS lesions of ND-LCH but little is known about functional changes observed in this disease.

OBJECTIVES: To search for CNS metabolic changes in NDLCH.

METHODS: Seven patients suffering from ND-LCH were investigated by 18F-FDG PET in this prospective study and compared with 21 healthy controls.

RESULTS: ND-LCH patients demonstrated recurrent abnormalities including bilateral hypometabolism in the cerebellum, the basal ganglia (caudate nuclei), frontal cortex and, bilateral, a relatively increased metabolism in the amygdalae (p < 0.001). Functional changes in these anatomical regions may be detected in the absence of any apparent lesion on MRI.

CONCLUSIONS: ND-LCH demonstrates a recurrent 18F-FDG PET metabolic signature. Our results suggest that 18F-FDG PET might be a useful tool for an early diagnosis of ND-LCH before neuroradiologic abnormalities appear.