Posttransplant acute limbic encephalitis

Posttransplant acute limbic encephalitis (PALE) is a rare neurological complication that occurs following allogeneic hematopoietic stem cell transplantation (HSCT). It is characterized by acute inflammation of the limbic system — the brain structures involved in memory, emotion, and behavior, including the hippocampus, amygdala, and surrounding temporal lobe regions. The condition typically manifests within the first few months after transplantation and is believed to be related to immune-mediated mechanisms, potentially involving donor-derived immune cells reacting against the recipient's central nervous system, though the exact pathogenesis remains incompletely understood. Some cases have been associated with human herpesvirus 6 (HHV-6) reactivation. Key clinical features include acute onset of confusion, short-term memory loss, seizures (often temporal lobe epilepsy), disorientation, personality changes, and emotional disturbances. Brain MRI typically reveals characteristic signal abnormalities in the medial temporal lobes, particularly the hippocampi, on T2-weighted and FLAIR sequences. Cerebrospinal fluid analysis may show mild pleocytosis and elevated protein levels. The condition can progress rapidly and may lead to significant cognitive impairment if not promptly recognized and treated. Treatment approaches are largely empirical due to the rarity of the condition and include antiviral therapy (particularly when HHV-6 reactivation is suspected), immunosuppressive agents such as corticosteroids, and anticonvulsant medications for seizure management. Outcomes are variable; some patients may recover partially or fully, while others experience persistent neurological deficits, particularly memory impairment. Early recognition and intervention are considered important for improving prognosis. There are currently no standardized treatment guidelines, and management is typically individualized based on the suspected underlying etiology and clinical severity.

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