Patient Perceptions of Mood, Cognition, and Fatigue: Lessons from the Incapacity Status Scale

Background: The Incapacity Status Scale (ISS) is a well-validated 16-item interview measuring living disability in multiple sclerosis (MS). However, like many subjective rating scales, it possesses shortcomings in assessing the multiple dimensions of patients’ complaints. In particular, subjective measurement items regarding mood, cognition, and fatigue in MS are often limited in their ability to capture the complexity of the features associated with disability in these areas.

Objectives: To assess the ability of the mood, cognition, and fatigability items of the ISS to accurately represent these constructs.

Methods: Retrospective chart review of patients who had undergone neuropsychological testing (N = 68) was performed at an outpatient MS clinic in a large medical center. Data collected included the ISS, the Behavior Rating Inventory of Executive Function (BRIEF), three mood inventories, six neuropsychological tests of cognition, and two fatigue inventories. Internal consistency analyses of the ISS and partial Spearman rank-order correlations, controlled for the effects of age, race, and gender, were conducted to examine the relationships among ISS mood, cognition, and fatigability items and external measures of those three constructs.

Results: Two ISS questions were excluded from internal consistency analysis due to high non-response rates: medical problems (86.8%) and sexual function (64.5%). Internal consistency for the ISS was strong (Cronbach’s α = .883). ISS mood was significantly correlated with the BRIEF (ρ = .300, p = .045) and three other inventories (ρ = .301, p = .032; ρ = .358, p = .009; ρ = .392, p = .001). ISS fatigue was significantly correlated with both fatigue inventories (ρ = .309, p = .029; ρ = .424, p = .008). ISS cognition was significantly correlated with only one of six cognitive tests (ρ = −.347, p = .008).

Conclusions: The ISS items on mood and fatigability appear to be valid construct measures. The cognition item fails to capture almost all dimensions of cognitive dysfunction in MS. Implications for the development and application of future subjective MS rating instruments are discussed.