Minimal clinically important difference of the Modified Fatigue Impact Scale in Parkinson's disease

Fatigue is a common and debilitating symptom of Parkinson's disease (PD) with no evidence-based treatments. While several fatigue scales are partially validated in PD the minimal clinically important difference (MCID) is unknown for any scale but is an important psychometric value to design and interpret therapeutic trials. We thus sought to determine the MCID for the Modified Fatigue Impact Scale (MFIS). This is a secondary data analysis from 94 PD participants in an acupuncture trial for PD fatigue. Standard psychometric approaches were used to establish validity and an anchor-based approach was used to determine the MCID. The MFIS demonstrated good concurrent validity with other outcome measures and high internal consistency. MCIDs values were found to be 13.8, 6.8 and 6.2 for the MFIS total, MFIS cognitive, and MFIS physical subscores respectively. The MFIS is a valid multidimensional measure of fatigue in PD with demonstrable MCID. •Fatigue is a common disabling symptom of Parkinson disease (PD) without treatment.•Minimal clinically important difference (MCID) is needed for PD fatigue trials.•We determined the MCID of the Modified Fatigue Impact Scale (MFIS).•The MFIS demonstrated good concurrent validity with other outcome measures.•The MFIS is a valid multidimensional fatigue outcome for PD fatigue trials.