135most frequently used tools were VAS and NRS single questions [ 14 , 48 ]. Fatigue
assessed with NRS was shown to be an independent outcome measure and sensitive
to change in patients with PsA [ 77 ]. Fatigue can also be assessed using more com-
plex scales that were adapted and validated for patients with PsA, namely the modi-
fi ed Fatigue Severity Scale (mFSS) and the Functional Assessment of Chronic
Illness Therapy—Fatigue (FACIT—Fatigue) [ 78 ]. The SF-36 vitality subscale has a
high correlation ( r = −0.76) with fatigue measures such as the FSS [ 79 ]. FACIT-
Fatigue demonstrated good reliability and validity and has the advantage of cover-
ing a broader concept of fatigue. However, good correlations have been shown
between the fatigue NRS and more complex scales, and the fatigue VAS is reported
to perform as well as or better than longer scales [ 14 , 80 ].
Assessment in Patients with SPA (axSpA and PsA)
with Generic Questionnaires
Health Assessment Questionnaire
The Stanford Health Assessment Questionnaire Disability Index (HAQ-DI) is
currently the most widely used measure of functioning and disability across rheu-
matic diseases, and in PsA studies as well [ 48 , 81 , 82 ]. Although the HAQ was
originally developed for RA, it is validated in PsA. The HAQ contains 20 items
that deal with diffi culties experienced with 8 categories of daily living. The HAQ
results in a total score between 0 (no disability) and 3 (severe disability) [ 73 ]. The
HAQ has good psychometric properties. In different contexts, this measure is
sensitive to change and is a good predictor of future disability and costs.
Specifi cally in PsA, the HAQ has been shown to be reliable, valid, and sensitive
to change in several PsA trials [ 65 , 70 , 71 , 83 , 84 ]. The interpretation of the HAQ
is slightly different in PsA than in RA. Whereas in RA, the cutoff for a minimally
important difference (MID) is 0.25, in PsA it is higher and has been suggested to
be about 0.35 [ 84 ].
The Health Assessment Questionnaire for the Spondyloarthropathies (HAQ-S)
(S = spondyloarthritis) is an adaptation based on the original HAQ [ 81 ], incorporat-
ing issues of physical functioning specifi c to patients with axial SpA. Items con-
cerning dressing, arising, eating, walking, hygiene, reaching, gripping, and errands
and chores have been taken unchanged from the original HAQ. In the HAQ-S, 5
specifi c items concerning neck function and static posture (driving a car, using a
rear-vision mirror, carrying heavy groceries, sitting for long periods, and working at
a desk) were added [ 85 ]. Ward et al. showed in a large US American cohort that the
values of HAQ-S increased over a median of 5 years at an average rate of 0.0168
units per year [ 86 ].
5 PROMs for Spondyloarthritis