Fatigue is a major problem in a wide range of (chronic) diseases including interstitial lung disease (ILD) and sarcoidosis. Fatigue is the most frequently described and globally recognized as a disabling symptom. The reported prevalence varies from 60% to 90% of sarcoidosis patients, and up to 25% of fatigued sarcoidosis patients report extreme fatigue. Also, patient with idiopathic pulmonary fibrosis (IPF) reported to suffer from 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. As a gradual and cumulative process, fatigue reflects vigilance decrement and decreased capacity to perform, along with subjective states that are associated with this decreased performance. It is a general psychophysiological phenomenon that diminishes the ability of the individual to perform a particular task by altering alertness and vigilance, together with the motivational and subjective states that occur during this transition. Consequently, there is reduced competence and willingness to develop or maintain goal directed behaviour aimed at adequate performance.

Several studies have reported that neither lung function tests nor chest radiographs correlate with nonspecific health complaints, including fatigue or QoL. Fatigue is often troubling to physicians to deal with because it does not relate directly to a physiologic abnormality, is difficult to quantify and hence to monitor, and is challenging to treat.

The Fatigue Assessment Scale (FAS) is now available in more than 15 languages. It is quick and easy to complete for patients, and not time consuming. It is also helpful for physicians and other health care workers in the follow-up of their patients in addition to the regular functional tests such as lung function tests. The FAS has proven to be a valid questionnaire to assess fatigue in patients with ILD, but also in many other patients with chronic diseases.

The FAS is a 10-item general fatigue questionnaire to assess fatigue. Five questions reflect physical fatigue and 5 questions (questions 3 and 6-9) mental fatigue.

An answer to every question has to be given, even if the person does not have any complaints at the moment. Scores on question 4 and 10 should be recoded (1=5, 2=4, 3=3, 4=2, 5=1). Subsequently, the total FAS score can be calculated by summing the scores on all questions (recoded scores for questions 4 and 10). The total score ranges from 10 to 50. A total FAS score < 22 indicates no fatigue, a score ≥ 22 indicates fatigue. All on-line versions of the FAS calculate the FAS scores automatically: a total score as well as mental and physical score will be provided.

In summary:
– FAS scores 10 – 21: no fatigue (normal)
– FAS scores 22 – 50: substantial fatigue
2 subgroups:
       fatigue: scores 22-34 
       extreme fatigue: scores ≥ 35

The Minimal Important Difference (MCID) is at least 4 points or 10% change of the baseline value.

References

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

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