The impact of illness intrusiveness on the relationship between cognition and mood in multiple sclerosis.

Abstract

Multiple sclerosis (MS) is an immune-mediated, inflammatory neurodegenerative chronic disease that affects the central nervous system and is characterized by substantial impacts on physical, cognitive, and psychological functioning. Clinically significant anxiety and depression are about 2-4 times as common in MS as in the general population, and are often associated with increased risk for morbidity and mortality, reduced medication adherence, increased risk for suicidal ideation, and reduced quality of life. Cognitive impairment, especially impaired information processing speed, is also common in MS and has continually been associated with mood disturbance in people with MS. However, research on potential mechanisms for this relationship has been sparse. Illness intrusiveness may be one such mechanism; this concept refers to the degree to which an illness and/or its treatment may interfere with important aspects of a person’s life, particularly participation in previously valued activities and interests. Although research has continually found relationships between illness intrusiveness and mood, research on illness intrusiveness and cognition has been sparse. The one published study in the literature found illness intrusiveness to mediate the relationship between verbal learning and depression in MS. The current study attempted to expand this literature by determining if impairment in processing speed as well as more general cognitive impairment was associated with illness intrusiveness and mood disturbance in MS. This study employed a retrospective cross-sectional design to answer this question. 199 participants with clinically definite MS were given both cognitive and mood measures. Cognitive measures included the Symbol Digit Modalities Test (Smith, A., 1982), the California Verbal Learning Test, second edition (Delis et al., 2000), the Brief Visuospatial Memory Test-Revised (Benedict, 1997), and the Controlled Oral Word Association Test (Benton, 1994). Illness intrusiveness was assessed using the Illness Intrusiveness Ratings Scale (Devins et al., 1983). Anxiety was measured using the anxiety subscale of the Hospital Anxiety and Depression Scale (Zigmond & Snaith, 1983). Depression was measured using the Patient Health Questionnaire-9 (Kroenke et al., 2001). Illness intrusiveness was found to mediate the relationship between processing speed and depression, ab = -.07, 95% CI [-.15, -.002 ], processing speed and anxiety, ab = -.06, 95% CI [-.12, -.02], and processing speed and more general mood disturbance, ab = -.08, 95% CI [-.13, -.0005]. This study also found that more general cognitive impairment did not have a significant relationship with either illness intrusiveness or mood symptoms. Thus, illness intrusiveness was found to be an important intermediary mechanism by which the primary cognitive impairment in MS, processing speed, impacts mood in this disease population. Conclusions, treatment implications, and directions for future research in light of these findings were discussed.