Central nervous system complications after allogeneic haematopoietic cell transplantation: best practice recommendations from the EBMT practice harmonisation and guidelines committee on epidemiology, outcome and neuroimaging.

CNS complications (CNSC) may occur in a significant proportion of patients after allogeneic haematopoietic cell transplantation (allo-HCT). They can be differentiated into infectious and non-infectious CNSC, such as vascular pathologies (e.g., bleeding, stroke), drug-related abnormalities, and CNS relapse of the underlying malignancy. Initiation of prompt and adequate diagnostics - mainly neuroimaging and cerebrospinal fluid (CSF) analyses - and treatment are crucial to improve the prognosis. Here, we report on the epidemiology, outcome, and neuroimaging of CNSC after allo-HCT. We also provide an overview of the special considerations for children with these complications. These findings and recommendations were developed during a multidisciplinary EBMT harmonisation workshop. Novel diagnostics, such as CSF next-generation sequencing (NGS) and special MRI sequences, are emerging and may improve the accuracy of diagnosis for selected CNSC. The prognosis of post-transplant CNSC is heterogeneous, with drug-related CNSC mainly having a favourable prognosis, while the outcome of CNS bleeding, CNS leukaemia, and cerebral fungal disease is still frequently dismal. A high level of awareness is crucial in the clinical routine - especially in distinct subgroups such as paediatrics - besides the development of novel algorithms, diagnostics, and treatment approaches to improve the outcome.