Fatigue is a very common and disabling symptom of multiple sclerosis (MS) that is challenging to characterize appropriately for both research and clinical practice. The emergence of the NIH PROMIS item banks provides new possibilities for the development of outcome measures that are brief and optimally targeted. Substantial evidence has accumulated regarding the use of the PROMIS SF 1.0 – Fatigue (MS) 8b short form to discriminate levels of fatigue among individuals who have MS. The short form was developed with input from MS patients and clinicians.
To establish minimal important difference (MID) estimates and interpretation tools for the PROMIS Fatigue (MS) 8b in MS populations.
Two observational studies were performed in MS populations, a cross-sectional study at two tertiary MS centers in the US (n=296) [US sample] and a longitudinal study in the UK MS Register cohort (n=384) [UK sample]. The analysis sample included patients with relapsing- or progressive MS, and those with Patient-Reported Web EDSS <7. Minimal important difference (MID) of PROMIS Fatigue (MS) 8b T-score was analyzed based on score changes over a 52-week follow-up using an anchor-based approach [UK sample]. An interpretative guide for PROMIS scores was also developed [US sample].
At baseline, study participants had a mean age of 44.5 – 49.9 years, and mean PROMIS Fatigue (MS) 8b T-score of 57.4 – 59.9. Three anchors met criteria and were used in the MID analysis [ i.e. PROMIS GHS fatigue question, GHS PHC global question, and the Fatigue Severity Scale]. The standard error of measurement [SD * √ (1 – reliability)] of baseline T-scores was 2.8. A score change of 3.4 – 4.0 points is proposed as MID criteria for minimal improvement or worsening in fatigue. A heatmap facilitating interpretation of scores based on fatigue concerns on individual items was developed. For example, a T-score of 60 represents a fatigue level characterized by (often) getting tired easily, (sometimes) being too tired to think clearly, and (some-) interference with physical functioning, in the last 7 days.
This research extends the evidence underpinning the applicability of the PROMIS Fatigue (MS) 8b in routine clinical practice and clinical research. The score interpretation guide may aid the integration of PROMIS scores into clinical decision-making as well as facilitate clinician-patient communication. MID estimates will be useful in evaluating fatigue over time.