Path to Illness Intrusiveness: What Symptoms Affect the Life of People Living With Multiple Sclerosis?

Objective: To determine the direct and indirect effects of physical, emotional, and cognitive impairments on illness intrusiveness in people with multiple sclerosis (MS).

Design: Secondary analysis of a cross-sectional data set collected in 2008 to identify sex differences in people living with MS.

Setting: Three MS clinics.

Participants: A random sample (N=189) of women and men diagnosed with MS after 1995 were recruited and evaluated in 2008.

Interventions: Not applicable.

Main outcome measure: Illness Intrusiveness Rating Scale (updated version using Rasch analysis).

Results: Path analysis yielded a model that was significant (nonnormed fit index, .9913; normed fit index, .9846) with adequate fit of the data to the model (goodness of fit index, .9781; χ²=21.41; P=.2084). The model explained 55% of the variance of illness intrusiveness. Only emotional and physical aspects were represented in the model because no cognitive impairment stayed after variable reduction. The model showed the complete mediation effect of fatigue on the physical function variables.

Conclusions: This project brings new evidence toward the conceptualization of illness intrusiveness as a construct allowing future interventions that wish to target illness intrusiveness or disease impact to be designed. It also presented statistical evidence of the importance of treating fatigue not only as a symptom but also as a consequence of other impairments.