[Partial regression of CNS lesions of Erdheim-Chester disease after treatment with 2-chlorodeoxadenosine and their full remission following treatment with lenalidomide].

INTRODUCTION Erdheim-Chester disease is a very rare syndrome affecting adult population. It typically causes hyperostosis of long bones, retroperitoneal fibrosis and widening of the aortic wall. Patients frequently suffer from disease-associated fevers and pain in the lower limbs. No guidelines are available for the treatment of this rare ailment. Therefore, we describe our experience with lenalidomide in a patient with poor treatment response to 2-chlorodeoxyadenosine. CASE Diabetes insipidus and neurological problems developing over 4 years were the first signs of the disease. The disease was diagnosed from histology of the bone marrow extracted from the ilium. At diagnosis, the patient had multiple infiltrates in the brain, widened wall of the thoracic and abdominal aorta, fibrotic changes to retroperitoneum and typical hyperostosis of the long bones of lower limbs with high accumulation of technetium pyrophosphate as well as fluorodeoxyglucose. First line treatment involved 2-chlorodeoxyadenosine 5 mg/m2 s.c. for 5 consecutive days every 28 days. There was no clear treatment response identifiable on the MR scan of the brain following the third cycle and thus 4th-6th cycle consisted of 2-chlorodexyadenosine 5 mg/m2 + cyclophosphamide 150 mg/m2 + dexamethasone 24 mg day 1-5 every 28 days. After the 6th cycle, MR showed partial regression of the brain lesions. PET-CT showed an increased accumulation of fluorodeoxyglucose in bone lesions. Second line treatment involved lenalidomide 25 mg/day days 1-21 every 28 days. Lenalidomide tolerance was excellent; the number of neutrophils and thrombocytes was within the physiological range throughout the treatment period. Follow-up MR showed complete remission of the brain lesions, while follow-up PET-CT showed further increase in fluorodeoxyglucose accumulation in the bones of lower limbs. CONCLUSION Treatment with 2-chlorodeoxyadenosine-based regimen provided partial remission of Erdheim-Chester disease lesions in the brain, while treatment with lenalidomide resulted in complete remission of these lesions. Fluorodeoxyglucose continues to accumulate in the long bones of lower limbs. We are unable to elucidate the reasons for complete remission of the disease in the brain as per the MR and its progression in the long bones according to PET-CT. Further testing of lenalidomide in the treatment of this disease is required to support further use of this perspective treatment option.