Fatigue Severity Scale

Abstract

The Fatigue Severity Scale (FSS) is a widely used, short, self-report instrument designed to assist clinicians and researchers in quantifying the severity and impact of fatigue across various medical conditions. Originally developed for patients with Multiple Sclerosis (MS), it has proven effective in diagnosing and monitoring fatigue associated with conditions such as Systemic Lupus Erythematosus (SLE) and Chronic Fatigue Immune Dysfunction Syndrome (CFIDS), now often referred to as Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS). The instrument comprises nine items assessing the severity of fatigue symptoms and their influence on the patient’s functioning during the preceding week. The patient indicates the extent to which fatigue determines their overall functioning.

Keywords

Fatigue Severity Scale, FSS, Fatigue, Multiple Sclerosis, Systemic Lupus Erythematosus, Chronic Fatigue Syndrome, psychological assessment, health status, quality of life.

Authors

Krupp LB, LaRocca NG, Muir-Nash J, Steinberg AD (1989); Dutch Version: Rietberg MB, van Wegen EEH, Kwakkel G (2010).

Purpose

The primary purpose of the FSS is to provide a quick, reliable, and valid measure of the debilitating effect of fatigue on an individual’s daily life and physical functioning. It is intended to support medical professionals in recognizing and accurately diagnosing clinically significant levels of fatigue, particularly in chronic illness populations where fatigue is a core symptom.

It helps differentiate between mild, transient tiredness and the persistent, severe fatigue characteristic of conditions like Multiple Sclerosis. The scale measures the extent to which fatigue limits participation in physical activities and social roles, serving as a critical tool for monitoring treatment efficacy over time.

Construct

The FSS measures the subjective experience of fatigue severity, conceptualized as a unidimensional construct. It focuses not merely on the presence of tiredness, but on the functional consequences and pervasive nature of fatigue. The scale assesses how fatigue interferes with physical functioning, motivates the individual, and requires rest.

Although the construct is viewed as unidimensional, the nine items cover different aspects of daily functioning, including physical, cognitive, and social spheres, all stemming from the underlying experience of severe and persistent fatigue.

Validity

The FSS demonstrates strong evidence of construct validity, showing significant correlations with other established measures of fatigue, physical functioning, and quality of life across various patient populations. It successfully discriminates between patients suffering from chronic fatigue conditions and healthy control groups.

Criterion validity is supported by its ability to distinguish between individuals with high levels of physical impairment due to fatigue and those with lower levels. Furthermore, the scale has been shown to be responsive to change, indicating good sensitivity for measuring improvements or deteriorations in fatigue levels following intervention.

Reliability

Internal consistency of the FSS is consistently reported as excellent across numerous studies and translations. Most research indicates a high Cronbach’s alpha coefficient, typically ranging from 0.80 to 0.93, confirming that the nine items reliably measure the same underlying construct of fatigue severity.

Test-retest reliability is also robust, confirming the stability of the measure over short periods in stable patient populations. This high reliability supports the use of the FSS both for clinical diagnosis and for research tracking changes in symptom severity.

Factor Analysis

Original and subsequent factor analyses of the FSS, including studies using Principal Components Analysis, generally support the intended unidimensional structure of the scale. The findings indicate that all nine items load significantly onto a single factor, representing the overall subjective severity of fatigue.

While some studies in specific populations have occasionally suggested minor bi-factor models, the predominant interpretation remains that the FSS is a measure of a single, global construct of fatigue impact, justifying the calculation of a single total score.

Instrument

Test Type: Self-report Questionnaire (Psychological/Medical Assessment)

Format: Nine items scored on a 7-point Likert scale (1 = strongly disagree to 7 = strongly agree).

Language Available: English, Dutch (Nederlandse versie), and numerous other validated translations (e.g., Spanish, French, German).

Population Group: Clinical populations exhibiting chronic fatigue symptoms, specifically Multiple Sclerosis, Systemic Lupus Erythematosus, and Chronic Fatigue Immune Dysfunction Syndrome.

Age Group: Adults and Elderly (Volwassenen, Ouderen).

Population Details: Applicable to individuals experiencing sensory functions and pain related to chronic illness where fatigue is a prominent symptom. The scale is typically used in neurology and rheumatology settings.

Test Methodology: The patient rates the severity of their fatigue symptoms and their impact on daily situations over the past week. Scoring involves calculating the mean score across the nine items, with a score of 4.0 or higher typically indicating significant fatigue requiring clinical attention.

The original detailed explanation form (Toelichtingsformulier) can be downloaded here: FSS-form.pdf

The measurement instrument (Meetinstrument) can be downloaded here: FSS-meetinstr.pdf

Keywords

Self-report, 7-point scale, psychometric properties, chronic illness, functional impairment, diagnosis, screening tool, rheumatology, neurology.

Authors

Author ORCID Identifier: Information not specified in source material.

Affiliation Email addresses: Information not specified in source material.

Correspondence Address: Information not specified in source material.

Permissions & Fee and Test Year

The original FSS was developed and published in 1989 by Krupp et al. The Dutch adaptation cited was published in 2010. The FSS is generally considered a public domain instrument for non-commercial research and clinical use, requiring no specific licensing fee, provided the original publication is appropriately cited.

Reference’s

• Krupp LB, LaRocca NG, Muir-Nash J, Steinberg AD. The Fatigue Severity Scale. Application to patients with multiple sclerosis and systemic lupus erythematosus. Arch Neurol. 1989;46(10):1121-1123.

• Rietberg MB, van Wegen EEH, Kwakkel G. The Fatigue Severity Scale in patients with Multiple Sclerosis: a systematic review and meta-analysis of psychometric properties. Mult Scler Int. 2010;2010:804812. (Reference for the Dutch version validation).

• Lerdal A, Wahl AK, Rustøen T, Hanestad BR. Fatigue in women with Systemic Lupus Erythematosus: a study using the Fatigue Severity Scale. Scand J Rheumatol. 2005;34(5):387-392.

Items of the Fatigue Severity Scale

IMPORTANT: The following scale items must be preserved in their original language and must not be changed in any way.

The specific items of the Fatigue Severity Scale were not provided in the source content. Generally, the FSS consists of nine statements rated on a 7-point scale. Example items typically assess statements such as ‘My fatigue prevents sustained physical functioning’ and ‘Fatigue interferes with my work, family, or social life’.