["Fatigue" in multiple sclerosis. Development and and validation of the "Würzburger Fatigue Inventory for MS"]

Fatigue is one of the most common, yet poorly defined, disabling symptoms in patients with multiple sclerosis (MS). Several fatigue scales have been developed, but rigorous psychometric methods have not always been applied and validation was mainly based on small numbers of patients. We therefore assembled a new fatigue scale from a set of widely used scales and assessed its psychometric properties in a large sample of MS patients.

Fatigue was assessed in 158 MS patients by four published quantitative scales: the Fatigue Severity Scale (FSS), Modified Fatigue Impact Scale (MFIS), MS-specific Fatigue Severity Scale (MFSS), and Visual Analogue Scale. From these a new fatigue scale, the Würzburg Fatigue Inventory for Multiple Sclerosis (WEIMuS), was assembled. It contains 17 items with values from 0 to 4. The WEIMuS scale was validated in a subgroup of 67 patients and a control group of 68 patients.

The MFIS and FSS but not the MFSS showed high internal consistency and split-half reliability. After applying factor analysis within the scales, fairly reliable and valid items originally found in the MFIS and FSS were selected to construct the final 17-item WEIMuS scale, which showed a high degree of reliability. In the validation study, varimax rotated factor analysis extracted two main factors corresponding to both cognitive and physical fatigue.

The new, two-dimensional WEIMuS showed good psychometric properties, is easy to use, and may therefore be a useful tool for the assessment of MS-associated fatigue. Multiple sclerosis patients suffer from different types of fatigue which could be attributed to cognitive and physical fatigue. Thus, MS-associated fatigue is different from common tiredness.