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Clinical neuropsychology in the management of myotonic dystrophy

In a previous issue of Muscle & Nerve, we outlined how psychological processes interact with biological and social factors to affect quality of life in muscle disorders. We then described the use of psychological interventions—focusing mainly on talking therapies—for improving quality of life, mood, and general functioning. As in the case of well-cited reviews describing the clinical management of myotonic dystrophy, neuropsychological assessment and cognitive rehabilitation were not described in detail in our article. The work by Fujino et al. in this issue of the Journal suggests that, in the care of patients with myotonic dystrophy (type 1) at least, our lack of attention to cognitive rehabilitation may have been an oversight. Therefore, in this editorial, we discuss the clinical implications presented by Fujino et al., taking the opportunity to describe the potential for cognitive rehabilitation for myotonic dystrophy. Fujino and colleagues observed that a large proportion of their participants had quite severe myotonic dystrophy and demonstrated impairment in at least 1 cognitive domain (i.e., scores at least 2 standard deviations from population averages). Impairment occurred most frequently in the domains of executive functioning, processing speed, attention, and visuoconstruction. Although their study included no controls for the impact of marked motor impairment, this finding adds to a body of work showing that many people with myotonic dystrophy type 1 have cognitive difficulties. Consistent with existing work, a significant proportion of participants in the sample recruited by Fujino et al. demonstrated comorbid behavioral symptoms/changes—with higher levels of apathy and depression apparent in the sample. The etiology of cognitive and behavioral symptoms in Fujino et al.’s sample was unclear. Other studies found an association between unstable cytosine–thymine–guanine (CTG) repeat expansion size and cognitive test performance and behavior changes in myotonic dystrophy. This is unsurprising given that, in myotonic dystrophy type 1, a positive association exists between brain pathology and CTG repeat expansion, whereas the extent of white-matter lesions is positively correlated with cognitive impairment and behavioral symptoms. In addition, other contextual factors—which may be less dependent on underlying brain pathology— may also affect cognitive functioning. Reactive depression, perhaps resulting from difficulties adjusting to physical symptoms, may worsen performance on cognitive testing; fatigue, sleepiness, or pain may also lead to problems with effort. Importantly, Fujino et al. demonstrated that performance on several cognitive tests was positively correlated with psychosocial aspects of quality of life. Their cross-sectional design did not allow us to disentangle the direction of influence between these variables. Yet, this observation does raise the possibility that an improvement in cognitive symptoms, or their impact on functioning, could lead to an improvement in quality of life. Although a caveat is that some reduced insight may be protective of mood, cognitive rehabilitation may offer a means to improve outcomes for many people with myotonic dystrophy.