A Case Example of the Impact of Fatigability on Balance Outcome Measurement in a Person with Multiple Sclerosis

Background: Fatigue, the feeling of tiredness or exhaustion, is a common and disabling symptom of multiple sclerosis (MS). It must be differentiated from fatigability, which is an objective change in physical performance after repetition. There is a small but growing body of literature that describes the impact of fatigability on outcome measures that are frequently utilized in the management of people with MS.

Objectives: The purpose of this case example is to illustrate a granular perspective of fatigability-induced changes in a commonly used balance outcome measure after even short periods of physical activity in a person with MS.

Methods: A 62-year old man with a 12-year history of relapsing-remitting MS (EDSS = 4.5, Disease Steps and Patient-Determined Disease Steps scores of 3) consented to participate in this case example. Baseline data included the Modified Fatigue Impact Scale (MFIS), the 12-Item Multiple Sclerosis Walking Scale (MSWS-12), and the Berg Balance Scale (BBS). The BBS consists of 14 functional items, each of which is scored on a scale from 0-4 for a score range of 0-56. After conclusion of the baseline BBS (BBS-pre), the person then underwent a standard 6-Minute Walk Test (6MWT). One minute after completing the 6MWT, the person was retested on the BBS (BBS-post). The difference between BBS-pre and -post was calculated for each of the 14 BBS items and the total score. The total BBS score difference (ΔBBS) was compared to previously published MCID values (3 and 6 points).

Results: Aside from the MS diagnosis, the person's medical history was otherwise unremarkable. Baseline scores were as follows: MFIS=47/84; MSWS-12=88/100; 6MWT distance=231m. The BBS total score changed from 42/56 (BBS-pre) to 33/56 (BBS-post) resulting in a ΔBBS of 9 points. The items that declined were sitting to standing (-1), retrieve object from floor (-1), turning to look behind (-1), placing alternate foot on stool (-1), and standing on one foot (-3). The remaining 9 items did not change.

Conclusions: The ΔBBS exceeded published MCID values, indicating a clinically important deterioration in balance as measured by the BBS after the 6MWT. There is evidence for adequate 1-week test-retest reliability of the BBS in people with MS. This case exemplifies that the BBS can vary beyond the MCID even after short bouts of physical activity. In this case, it can be interpreted that this person's balance became markedly worse after walking at a self-selected pace for only 6-minutes. Additional research is warranted to further examine the short-term reliability of the BBS in people with MS. In addition, further study may clarify which elements of the BBS are most susceptible to fatigability-induced changes.