Psychometric properties of patient-reported outcome measures, measuring fatigue in patients with multiple sclerosis, a systematic review.

Background: Multiple sclerosis (MS) is a chronic, inflammatory, degenerative disease of the central nervous system. One of the most common and disabling symptoms is fatigue. More than 80% of people with MS experience fatigue, which has a negative impact on their quality of life and level of independence in daily activities. The multidimensional nature of fatigue makes it essential to understand its impact from the patient's perspective. Patient-reported outcomes (PROs), defined by the FDA as "any report of a patient's health status that comes directly from the patient, without interpretation of the patient's response by the physician or other health care professional," were created to address this need.

Objectives: To identify and describe patient-reported outcomes (PROs) that measure the level of fatigue specific to patients with multiple sclerosis. To evaluate and analyze the quality of psychometric properties, methodological quality, and risk of bias of patient-reported outcomes that measure the level of fatigue specific to patients with multiple sclerosis.

Methods: A systematic psychometric review was conducted and framed according to the standards of the Consensus for the Selection of Measurement Instruments (COSMIN) (Mokkink et al., 2010).

Results: A total of 34 studies were included, from which a total of 40 references were extracted, as some studies reported two or more PROMs simultaneously. The evaluation and analysis of the risk of bias shows that the studies present a heterogeneous classification depending on the psychometric property evaluated, i.e. while the frequency of studies classified with low risk of bias is higher in measurement properties such as; structural validity; 25 studies (64.10%), internal consistency 25 studies (64.10%), criterion validity: 29 studies (74.36%). There is also a high frequency of studies rated as high or unclear risk of bias, mainly in psychometric properties such as reliability 19 studies (48.71%), cross-cultural validity measurement invariance 13 studies (33.33%).

Conclusions: PRO instruments are the best way to know the patients' perception of their symptomatology in this case of fatigue, which will undoubtedly contribute to a better approach and better intervention strategies in a personalized way, another component in the improvement of the quality of care and in line with the new paradigm of patient-centered care, which requires an assessment of fatigue by means of a PRO instrument. Therefore, it is of utmost importance to consider the current standards in the development of these instruments for a correct use and interpretability of their results.