Biphasic patterns of memory deficits following moderate-dose partial-brain irradiation: neuropsychologic outcome and proposed mechanisms

To identify the longitudinal neurobehavioral characteristics of the early-delayed and late-delayed effects of partial-brain radiotherapy for patients with supratentorial brain tumors with favorable histology. This study improves on previous attempts to identify radiation effects, because of the inclusion of baseline measures and the use of subjects as their own controls.

Ten neuropsychologic domains were measured in 12 patients at baseline (post-surgery and immediately before initiation of radiotherapy), and followed trimonthly for 1 year. Four to six patients were examined at 2 and 3 years postbaseline.

Patients were impaired at baseline compared with controls only in visual memory and sentence recall, but demonstrated significant improvement in visual memory by 2 years postbaseline. Speed of processing information also showed a slope of improvement over 2 years. Retrieval from verbal long-term memory was impaired at 1.5 months postcompletion of radiotherapy, but recovered to baseline levels by 1 year. At 2 years postbaseline, long-term memory retrieval demonstrated a decline, but remained unchanged at 3 years.

Long-term memory appears to be sensitive to the effects of radiotherapy. We confirmed our previous findings of a decrement with rebound during the early-delayed period, and propose that these findings are consistent with demyelination/remyelination. Decrement was observed again at 2 years postbaseline, which suggests that memory retrieval may be the earliest marker of late-delayed effects. These neurocognitive patterns are consistent with leukoencephalopathy. Confirmation of these observations will be possible if neuropsychologic testing with the same sensitivity can be incorporated into national collaborative trials.