Our centre monitors 23 patients with Langerhans cell histiocytosis (LCH) and 2 patients with Erdheim-Chester disease. Of this group of 25, 8 patients have some form of histiocytosis-associated CNS involvement. Four of the 8 patients had been referred to our centre for diabetes insipidus that developed in adulthood. In these patients, PET-CT was performed to detect potential extracranial signs of the disease that had induced diabetes insipidus. PET-CT revealed extracranial pathological changes; histological examination was performed on biopsies from these lesions. LCH was confirmed in two patients and Erdheim-Chester disease in the other two. In the fifth patient, an intracranial expansion from the occipital bone was detected that compressed the brain in the area of visual cortex and caused visual field failure. A follow-up MR and PET-CT were performed after a last cycle of cladribine treatment and confirmed complete remission. The sixth patient with headache had suggestive yet unclear MR finding in the area of temporal lobe. The MR signal changes could have been interpreted as delayed post-radiation changes or as LCH infiltrations of this part of the brain. PET-CT imaging confirmed pathological accumulation of fludeoxyglucose in this area, corresponding to malignant infiltration. As detected during a follow up examination, fludeoxyglucose accumulation declined from SUV 12 to SUV 5 and confirmed sensitivity of the disease to the 2 administered cycles of
cladribine. The seventh and eighth patient had LCH diagnosed in childhood but the neurological sequelae, such as ataxia and dysarthria, did not occur before they reached adulthood. PET-CT examination showed reduced accumulation of fludeoxyglucose in cerebellum and in basal ganglia, corresponding to an MR depiction of atrophy in this area, and, at the same time, excluded a relapse of the disease. Conclusion: The whole body PET-CT examination might be useful in identification of the causes of diabetes insipidus and it may confirm active
foci of LCH in the brain, while decreased fludeoxyglucose accumulation is a typical sign of delayed neurodegenerative changes rarely occurring following long-term course of LCH.