Psychiatric-Medical ComorbidityFatigue in patients with sarcoidosis, compared with the general population
Introduction
Sarcoidosis is an inflammatory disease, characterized by noncaseating granuloma. All organs in the body can be affected by sarcoidosis. Besides the lungs, the most often affected organs are the lymph nodes, skin and eyes. Symptoms often reported by sarcoidosis patients are pain, cough, breathlessness, reduced exercise capacity and arthralgia [1]. Generally, sarcoidosis patients report reduced health-related quality of life and mental health [2], [3], [4], [5], [6]. One symptom very often found in sarcoidosis patients is fatigue. Although fatigue is a common complaint in general medical practice, there are several diseases where fatigue is often found, e.g., cancer, multiple sclerosis, rheumatoid arthritis and depression [7]. Among sarcoidosis patients, fatigue was elevated in many studies. De Kleijn et al. [8] performed a systematic review, comprising 20 studies. The incidence rates of fatigue in these studies ranged from 33% to 100%. Four of the 20 studies had more than 200 patients, with the frequency of fatigue ranging from 71% to 80%.
There are several questionnaires measuring fatigue. Among the 20 studies reported in the review on fatigue in sarcoidosis [8], the most often used questionnaire was the Fatigue Assessment Scale (FAS) [9]. Other fatigue scales adopted to assess sarcoidosis patients were the Energy and Fatigue Scale of the World Health Organization Quality of Life Assessment Instrument–100 (WHOQOL-100) [10], the Fatigue Scale (FS) [11] and the Functional Assessment of Chronic Illness Therapy–Fatigue (FACIT-F) [12]. Another fatigue questionnaire is the Multidimensional Fatigue Inventory (MFI). This instrument was developed by Smets et al. [13], especially for use in cancer patients. Although the MFI has not been validated in sarcoidosis patients, it seems to be a promising assessment tool since it comprises five dimensions of fatigue and since norm values for the general population are available [14].
Whether age and gender influence the incidence of fatigue in sarcoidosis remains an open question. Two studies found higher mean scores in females compared with males [15], [16]. Other studies failed to detect such gender differences. However, even if the mean scores of female patients were higher than those of males, it is not known whether this gender effect is specific for sarcoidosis, or whether gender differences are also common in the general population. Furthermore, little is known about age effects of fatigue in sarcoidosis. While in a Dutch sample of sarcoidosis patients there was no age effect on fatigue, in a US sample younger sarcoidosis patients reported elevated degrees of fatigue (beta=0.21) [17]. A comprehensive sample of more than 1000 Dutch sarcoidosis patients failed to show an age effect on fatigue [9]. When studies do not detect age effects within samples of patients, one should not conclude that age was irrelevant. Given that there were pronounced age differences in the general population, which disappear in samples of patients, the impact of the disease is nevertheless age dependent. Finally, many of the published investigations of fatigue in sarcoidosis were performed in the Netherlands; therefore it is important to test the effects in other countries.
The aims of this paper were
- (1)
to determine the degree of fatigue in sarcoidosis, compared with the general population,
- (2)
to assess age and gender effects of fatigue in sarcoidosis in relation to those effects found in the general population, and
- (3)
to test and to compare the psychometric quality of the MFI (20 items), the FAS (10 items) and a single-item question concerning fatigue, applied to sarcoidosis in a large German sample.
Section snippets
Sample of patients suffering from sarcoidosis
This study was performed in collaboration with the German Sarcoidosis Society in 2009. All members of this society (N=4100) were invited to take part in the study. They received a letter, together with a questionnaire and the informed consent form. A total of 1270 letters (31%) were sent back. Fifteen of these could not be used because the participants wrote their names on the questionnaire which was in contradiction to the anonymization procedure. Fifty-eight questionnaires could not be
Comparison between sarcoidosis patients and the general population
Since normative data of the MFI in the general population are available, comparisons between sarcoidosis patients and the general population are possible. Fig. 1 illustrates these comparisons. While there is a nearly linear age trend (increasing fatigue with increasing age) in the general population for both genders, this trend does not occur in the sample of patients. The differences between patients and the general population are most pronounced for young people, and in the age group >70
Discussion
Fatigue proved to be a significant feature of sarcoidosis patients. Both questionnaires reached similar percentages of fatigue (70% and 68%, respectively). This is somewhat lower than the results found in the Netherlands (83%) and in the USA (75%) [17], obtained with the FAS. On the basis of FAS mean scores, our results (mean=26.3) are also similar to those of the Netherlands (mean=30.3) and of the USA (mean=27.1). The prevalence of fatigue in sarcoidosis patients is high compared with other
Acknowledgment
This study was supported by the German Sarcoidosis Society (Deutsche Sarkoidosegesellschaft), and their members' willingness to participate in this survey is greatly appreciated.
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