Types of fatigue in sarcoidosis patients
Introduction
Sarcoidosis is a disseminated granulomatous disease of unknown origin in which practically every organ can be involved. Lungs are the most commonly affected organ, however involvement of other organ systems such as lymph nodes, skin, eyes, muscles, heart, and joints are frequently observed. Symptoms can vary considerably depending on the specific organs involved and the severity of the granulomatous inflammation [1]. In addition to various symptoms related with the affected organs, patients often suffer from fatigue [2].
The etiology of fatigue associated with sarcoidosis is usually multifactorial. These include the release of cytokines from the granulomas [3], [4], [5] as a function of the disease itself and/or depression [6], weight gain, exercise intolerance, or altered sleep patterns as a result of disease related problems. Although to date no accepted definition of fatigue exists, several researchers have proposed to divide fatigue into at least two categories: physical and mental fatigue [7], or passive and active fatigue [8]. However, another study considers fatigue as a one-dimensional concept [9]. In this latter study, fatigue is regarded as a subjective experience, as measured by the Fatigue Assessment Scale (FAS).
Fatigue is the most frequently (71%) reported symptom in the sarcoidosis population in the Netherlands [2]. Moreover, fatigue appeared to be related with worse Quality of Life (QOL) [10], cognitive failure [11], and depressive symptoms [12]. Since there are no medications available for patients with fatigue, it is important to educate these patients to successfully cope with their fatigue. However, patients appear to experience variations in the type of fatigue [13], making it difficult to apply one universal coping strategy to all patients. Therefore, it is important in clinical practice to identify the possible types of fatigue which will ultimately enable healthcare providers to tailor the intervention appropriately to individual patients.
Sharma [13] described four types of fatigue in sarcoidosis: 1) Early-morning fatigue, where the patient arises with feelings of inadequate sleep; 2) Intermittent fatigue, where the patient wakes up normally but feels tired after a few hours of activity. After a short rest, the patient is able to resume activity, succeeded by another period of fatigue; 3) Afternoon fatigue, where the patient arises in the morning with adequate energy but feels exhausted in the early afternoon. As a result, the patient goes to bed early and stays in bed until the next morning; 4) Post-sarcoidosis chronic fatigue syndrome. This was recently identified [14] and occurs in about 5% of patients who seemingly have recovered from active sarcoidosis. In this condition, the patients complain of fatigue despite the absence of physical signs of sarcoidosis [13]. In our study, it was not possible to examine the post-sarcoidosis fatigue, because most of the participating patients had chronic sarcoidosis. Studies examining empirical evidence for the remaining three types of fatigue in sarcoidosis patients are needed to understand the challenges these patients encounter. However, this evidence is currently lacking in sarcoidosis.
Types of fatigue have been described in patients other than sarcoidosis such as with chronic heart failure [15], and were provided with empirical evidence by means of Latent Cluster Analysis (LCA) [16]. The purpose of LCA is to find the minimal number of clusters that best describe the associations between the observed indicators, such that individuals belonging to the same cluster are similar to one another, but differ from individuals in other clusters [17]. However, the classifications in fatigue found for chronic heart failure cannot be applied to sarcoidosis as the disease process is different from chronic heart failure which may influence the results.
The aims of this study were 1) to examine whether fatigue in sarcoidosis can be subdivided in types of fatigue: Early-morning fatigue, Intermittent fatigue, and Afternoon fatigue as previously described by Sharma [13] by means of LCA and 2) to describe the demographic, psychological, and clinical characteristics of the resulting clusters.
Section snippets
Study subjects
All sarcoidosis patients (n = 588) known at the outpatient clinic of ild care center of the Department of Respiratory Medicine of the Maastricht University Medical Centre, a referral centre for Sarcoidosis in the Netherlands, were asked to participate in this study. Of these patients, 434 (74%) participated in this study (see Fig. 1 for the patients selection). Patients were diagnosed with sarcoidosis based on consistent clinical features and bronchial alveolar lavage fluid analysis results. The
Results
Table 1 provides the information for model selection. As shown, a solution with three clusters resulted in the lowest BIC value. Moreover, its p-value for the goodness-of-fit test indicated that there was no need to reject this model in favor of a more complex model. The Wald tests reported in Table 2 show that all indicators were significantly related to the three clusters (p < 0.01 for all six indicators).
The cluster-specific means and percentages on the six indicators are enumerated in Table 3a
Discussion
The aims of this study were 1) to examine whether fatigue in sarcoidosis can be subdivided in types of fatigue: Early-morning fatigue, Intermittent fatigue, and Afternoon fatigue as previously described by Sharma [13] by means of LCA and 2) to describe the demographic, psychological, and clinical characteristics of the resulting clusters.
LCA revealed three clusters: a subgroup with mild or no complaints of fatigue (MF patients), a subgroup with complaints of fatigue that varied during the day
Acknowledgments
This project was financially supported by a grant of the Dutch Sarcoidosis Society Amsterdam, the Netherlands. We thank Niels Opdam and Petal Wijnen for the data collection.
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