PNR-41: AN UNUSUAL CASE OF CEREBELLAR LANGERHANS CELL HISTIOCYTOSIS RELAPSE POST BONE MARROW TRANSPLANT FOR SYSTEMIC DISEASE

INTRODUCTION: Langerhans cell histiocytosis (LCH) is a rare disease of the monocyte macrophage system. Presentation is varied as is the spectrum and course of disease. Central nervous system (CNS) LCH may present either with tumorous lesions, most commonly pituitary, or non-tumorous (neurodegenerative) entities most commonly characterised by changes in the cerebellum, basal ganglia +/- pons. We report a case of a 3 year old girl presenting with cerebellar tumoral LCH 3 years after initial presentation with severe systemic disease. CASE: Initial presentation was at 5 months of age with multisystem LCH including widespread involvement of skin, bone and haematopoietic system. Skin biopsy confirmed the diagnosis. She subsequently received an allogeneic matched unrelated transplant for refractory haematopoietic disease 4 months after diagnosis. She remained free of disease until presenting with polyuria and polydipsia 2 years post-transplant and was subsequently diagnosed with diabetes insipidus and growth hormone deficiency. While awaiting a routine MRI brain she developed signs of raised intracranial pressure and MRI with contrast confirmed the presence of a large left posterior fossa mass solid, with homogenous enhancement and cystic areas, abnormal spectroscopy pattern, minor diffusion restriction and associated triventricular hydrocephalus. Two-stage macroscopic resection was attained after histological confirmation of histiocytosis. With the exception of CD1a and Langerin negativity, in contrast with initial diagnostic skin biopsy, the lesion was consistent with a diagnosis of LCH. BRAF V600E mutation was present on CNS and skin sample. Screening for active systemic involvement was negative. A close clinical and radiological surveillance approach was adopted.