Fatigue is a major problem in a wide range of chronic diseases, including interstitial lung disease (ILD) and sarcoidosis. It is one of the most commonly reported and globally recognized disabling symptoms. The reported prevalence ranges between 60% and 90% in sarcoidosis patients, and up to 25% report extreme fatigue. Patients with idiopathic pulmonary fibrosis (IPF) also frequently experience substantial fatigue. Fatigue is defined as “an experience of tiredness, dislike of present activity, and unwillingness to continue”, or as a “disinclination to continue performing the task at hand and a progressive withdrawal of attention” from environmental demands.

Fatigue can be understood as a gradual and cumulative process, characterized by reduced alertness, decreased performance capacity, and diminished motivation to sustain goal-directed behaviour.

Several studies have reported that neither lung function tests nor chest radiographs correlate with nonspecific health complaints, including fatigue or quality of life (QoL). Fatigue is challenging for clinicians because it does not directly relate to measurable physiological abnormalities, is difficult to quantify and monitor, and remains hard to treat.

The Fatigue Assessment Scale (FAS) is now available in over 25 languages. It is a brief and easy-to-complete questionnaire for patients and a valuable tool for clinicians to monitor fatigue alongside standard functional assessments, such as lung function tests. The FAS has been validated as a reliable questionnaire for assessing fatigue in patients with ILD, as well as in many other chronic conditions.

The FAS is a 10-item questionnaire designed to assess general fatigue. Five questions measure physical fatigue, while five (items 3 and 6–9) assess mental fatigue.

An answer must be provided for every question, even if the respondent has no current complaints. Scores for questions 4 and 10 are reversed (1=5, 2=4, 3=3, 4=2, 5=1). The total FAS score is calculated by summing the scores of all items, including the recoded values for questions 4 and 10. The total score ranges from 10 to 50, with a score <22 indicating no fatigue and ≥22 indicating fatigue. Online versions of the FAS automatically calculate total, mental, and physical fatigue scores.
The Minimal Clinically Important Difference (MCID) is defined as a change of ≥4 points or ≥10% from baseline.

Summary
FAS score 10–21: no fatigue (normal)
FAS score 22–50: substantial fatigue
Fatigue: score 22–34
Extreme fatigue: score ≥35

References
Hendriks C, Drent M, Elfferich M, De Vries J. The Fatigue Assessment Scale (FAS): quality and availability in sarcoidosis and other diseases. Curr Opin Pulm Med 2018; 24 (5): 495-503. https://pubmed.ncbi.nlm.nih.gov/29889115
Drent M, Lower EE, De Vries J. Sarcoidosis-associated fatigue. Eur Respir J 2012; 40: 255–263. http://www.ncbi.nlm.nih.gov/pubmed/22441750
Kleijn WPE, De Vries J, Wijnen PAHM, Drent M. Minimal (clinically) important differences for the Fatigue Assessment Scale in sarcoidosis. Respir Med 2011; 105: 1388-95. http://www.ncbi.nlm.nih.gov/pubmed/21700440
De Vries, Michielsen H, Van Heck GL, Drent M. Measuring fatigue in sarcoidosis: the Fatigue Assessment Scale (FAS). Br J Health Psychol 2004; 9: 279-91. http://www.ncbi.nlm.nih.gov/pubmed/15296678

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