Disability in multiple sclerosis: a reference for patients and clinicians

Abstract

Objective: To create a reference table of disability outcomes in multiple sclerosis (MS) that would enable patients to rank their disability relative to others' with similar disease duration and to develop a cost-effective research tool for comparing MS severity across patient populations and time periods.

Methods: The North American Research Committee on Multiple Sclerosis (NARCOMS) Registry collects disability data from patients with MS on a validated, 9-point Patient-Determined Disease Steps (PDDS) scale. We compiled the Disability Expectancy Table, which displays cumulative frequencies of PDDS scores for each year of disease duration, from 0 to 45 years. We also tabulated disease duration-adjusted mean ranks of PDDS scores, referred to as Patient-derived MS Severity Scores (P-MSSS).

Results: The cohort consisted of 27,918 NARCOMS enrollees, 72.7% of whom were female and 90.1% of whom were white. Mean age at symptom onset was 30.1 ± 10.1 years, and age at enrollment was 47.1 ± 11.0 years. The Disability Expectancy Table and P-MSSS afford a detailed overview of disability outcomes in a large MS cohort over a 45-year period. In the first year of disease, 15% of patients reported need of ambulatory aid, and 4% needed bilateral assistance or worse; after 45 years of disease, 76% of patients required ambulatory aid, and 52% bilateral assistance or worse. Proportion of patients who reported minimal or no interference in daily activities (PDDS ≤ 1) declined from 63% in the first year to 8% after 45 years of disease.

Conclusion: The Disability Expectancy Table allows individual patients to determine how their disability ranks relative to NARCOMS enrollees with the same disease duration. P-MSSS may be used to compare disability across patient populations and to track disease progression in patient cohorts. P-MSSS does not require a formal neurologic examination and may therefore find wide applicability as a practical and cost-effective outcome measure in epidemiologic studies.

Figure 1. Disability Expectancy Table

The Table displays cumulative frequency distribution of Patient-Determined Disease Steps (PDDS) among North American Research Committee on Multiple Sclerosis (NARCOMS) registrants for each year of disease duration, from year 0 (topmost stripe) to year 45 (bottommost stripe). Each stripe consists of 9 segments corresponding to 9 PDDS grades. Color code for PDDS is provided (e.g., segment corresponding to PDDS = 0 is shown in orange, PDDS = 1 segment in peach). To illustrate the use of the Disability Expectancy Table, consider a hypothetical patient with self-reported mild disability (PDDS = 1, color-coded peach) after 5 years of disease. The boundaries of PDDS = 1 segment in year 5 stripe (sixth from the top) extend from 32% to 44% on the x-axis, which means that after 5 years of disease, 32% of NARCOMS registrants have PDDS <1, 12% have PDDS = 1, 44% of patients have PDDS ≤1, and 56% have PDDS >1. Thus, the patient in question is doing a little better than an average patient, but worse than approximately one-third of patients with disease duration of 5 years. By definition, mean rank (Patient-derived Multiple Sclerosis Severity Score [P-MSSS]) is the midpoint of each segment (i.e., average of the minimum and maximum ranks). P-MSSS data are shown in figure 2.

Figure 2. Patient-derived Multiple Sclerosis Severity Score Table

The format of this Table follows that of Global Multiple Sclerosis Severity Score (MSSS) Table with Patient-Determined Disease Steps (PDDS) on the x-axis and years of disease duration on the y-axis. To maintain consistency with MSSS, the Patient-derived MS Severity Scores (P-MSSS) values are reported in deciles, rather than percent. A different color is used for each decile of P-MSSS; color code is provided at the bottom of the Table.