Mechanisms of Chemotherapy-Induced Cognitive Disorders: Neuropsychological, Pathophysiological, and Neuroimaging Perspectives
Recent studies have indicated the frequent occurrence of neuropsychologic deficits and cognitive complaints after systemic cancer chemotherapy. Most early reports were retrospective, but prospective longitudinal studies are underway. Although the available evidence suggests a fairly diffuse pattern of changes, memory and executive functions could be preferentially affected. Preliminary data also suggest that some individuals might be more vulnerable than others, leading to investigation of genetic and other risk factors. The greatest gap in our knowledge regarding chemotherapy-related cognitive changes is a lack of understanding of the mechanism or mechanisms that account for the observed changes. Several pathophysiological candidates include direct neurotoxic effects leading to atrophy of cerebral gray matter (GM) and/or demyelination of white matter (WM) fibers, secondary immunologic responses causing inflammatory reactions, and microvascular injury. Altered neurotransmitter levels and metabolites could constitute an additional mechanism related to neurotoxic effects. Advanced brain imaging techniques can directly or indirectly assess many of these mechanisms, but to date there has been very limited application of these tools. Morphometric magnetic resonance imaging (MRI), functional MRI (fMRI), diffusion tensor imaging (DTI), and MR spectroscopy (MRS) are noninvasive techniques that could yield important complementary data regarding the nature of neural changes after chemotherapy. Electrophysiological studies and targeted molecular imaging with positron emission tomography (PET) could also provide unique information. We review the minimal imaging data available at present and also note studies of other brain disorders or treatment effects that might serve as a model for imaging chemotherapy-induced changes. Large-scale prospective studies are needed to help isolate the pathophysiological mechanisms underlying the cognitive deficits associated with chemotherapy.