New insights in radiation-induced leukoencephalopathy: a prospective cross-sectional study

Background Radiation-induced leukoencephalopathy (RIL) is the most threatening delayed complication of cerebral radiotherapy (RT) and remains roughly defined by cognitive dysfunction associated with diffuse FLAIR MRI white matter hyperintensities after brain irradiation. We documented clinical, neuropsychological, and radiological aspects of RI in order to refine diagnostic criteria. Methods Patients referred to our center for deterioration in cognitive complaint at least 6 months after completing a focal or whole brain RT underwent a systematic cross-sectional assessment including clinical examination, neuropsychological tests, and a standardized MRI protocol. Patients with progressive tumor were excluded. Results Forty patients were prospectively enrolled. Of these, 26 had received a focal RT, median dose of 53 Gy (range 50 to 60), and 14 had received a whole brain RT, median dose of 30 Gy. Cognitive complaints, gait apraxia, and urinary troubles were reported in 100, 67, and 38% of cases, respectively. On neuropsychological examination, patients displayed a global and severe cognitive decline through a subcortical frontal mode. The cognitive changes observed were not hippocampic, but related to executive dysfunction. On MRI, 68% of the patients had extensive FLAIR hyperintensities with anterior predominance, 87% had brain atrophy, and 21% had intraparenchymal cysts. T2*-weighted MRI showed small asignal areas in 53% of the patients. These abnormalities are evocative of cerebral small vessel disease. Fractional anisotropy in the corpus callosum correlated with the cognitive evaluation. No differentiation in terms of cognitive and MRI features could be made between patients treated with focal brain RT (glioma) and patients treated with WBRT (for brain metastases or PCNSL). Conclusions RIL can be defined by clinical symptoms (subcortical frontal decline, gait apraxia, urinary incontinence) and MRI criteria (cortico-subcortical atrophy, spread FLAIR HI, T2* asignals). This condition mimics a diffuse progressive cerebral small vessel disease triggered by RT, independent of RT protocol.