[Validation analysis of selected psychometric features of Polish version of Modified Fatigue Impact...

Fatigue is one of the most frequent and most disabling symptoms in multiple sclerosis (MS), disturbing patients' daily life. The Modified Fatigue Impact Scale (MFIS) is composed of 21 items; it evaluates the impact of fatigue on three dimensions of quality of life of patients with multiple sclerosis: physical, cognitive and psychosocial. MFIS is easy and quick to perform. The patient scores between 0 and 84 points - the higher the score, the stronger the impact of fatigue on the patient's quality of life.

One hundred and twenty-two patients with clinically definite MS, according to McDonald criteria, were qualified for the study. All patients had neurological examination and their disability was assessed according to the Expanded Disability Status Scale (EDSS). Patients were asked to complete the MFIS, the Polish version of the generic scale SF-36, and a sociodemographic questionnaire. Clinical data related to the course of the disease and exacerbation of particular symptoms were collected by using a special questionnaire with the participation of a neurologist. Reliability analysis was done by estimating internal consistency of the scale using Cronbach's coefficient alpha. The theoretical validity was assessed by analysing correlations between MFIS scores and SF-36 and EDSS scores as well as convergent validity.

MFIS scale and its subscales correlate with Vitality and Mental Health in the highest degree. According to the strongest correlations between MFIS subscales, Physical Subscale correlates with generic subscales connected with physical functioning, Cognitive Subscale correlates with Mental Health and Psychosocial Subscale with Vitality and Social Functioning.

Both the reliability and validity of MFIS are satisfactory; the scale seems to be a valuable tool to evaluate the impact of fatigue on quality of life of patients with MS.