Sickness and behavior in ME/CFS (chronic fatigue syndrome)

Abstract

Background: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic debilitating condition characterized by physical and mental fatigue with a heightened sensitivity to exertion. To date, the causes are unknown. However, recently the condition has been implicated as a chronic sickness behavior state. That is, the adaptive changes in brain and behavior commonly following acute infection (experiences of malaise, fatigue, brain fog and so forth) seem to have become chronic and thus maladaptive, since no infectious agent is present. The condition is often debilitating, but no effective treatments are available, which implies that interventions are normally aimed at reducing symptoms and/or restoring or improving functioning. Furthermore, classifications are multiple and not empirically based. As such, there is a need for: (1) empirical investigations of how symptoms present and relate to each other and other measures of clinical importance; (2) evaluations of behavior medicine treatment approaches aimed at improving functioning and quality of life, and; (3) studies investigating sickness behavior processes in ME/CFS on both subjective and objective levels.

Aims: The overarching aims of the present thesis were to: (a) investigate factors of importance in ME/CFS, including; (b) symptom patterns and their relationships to health and functioning (Study I); (c) inflammatory markers implicated in sickness behavior and fatigue and their associations with common symptoms (Study III); (d) the level of subjective sickness behavior in ME/CFS, compared to chronic pain, primary care patients and the general population (Study IV), and; (e) evaluate the acceptability, safety and preliminary efficacy of an Acceptance and Commitment Therapy(ACT)-based behavior medicine treatment protocol aimed at increasing functioning and quality of life in ME/CFS (Study II).

Methods: All ME/CFS patients in the four studies were included after referral and diagnostic assessment (CDC and CCC or ICC criteria) at a tertiary specialist clinic. In Study I (n=106), a total of 14 common ME/CFS symptoms were quantified and latent symptom subgroups were explored. The relationship between latent symptom subgroups and measures of health and functioning were investigated. In Study II (n=40), the effects of the ACT treatment on measures of disability, symptoms and health-related functioning were investigated. In Study III (n=53), associations between inflammatory markers and common symptoms in ME/CFS were investigated. In Study IV, levels of subjective sickness behavior were investigated in, and compared between: patients with ME/CFS (n=40); patients with chronic pain (n=193); patients in primary care (n=168), and; individuals from the general population (n=163). The associations between sickness behavior and self-rated health, mental and physical health-related functioning were also explored.

Results: The results in Study I showed four distinct subgroups in which differentiated symptoms gathered representing inflammatory, pain, neurocognitive and autonomic symptoms respectively. The symptom subgroups overall showed significant correlations with important clinical measures, although rarely exceeding .50, indicating the importance of other factors. ACT-based behavior medicine treatment can be considered acceptable, safe and preliminary effective for patients with ME/CFS (Study II). In Study III, several inflammatory markers (β-NGF; CCL11; CXCL10; IL-7; TGF-β-1 and; TNF-ɑ) significant associations with common symptoms (post-exertional fatigue; impaired cognitive processing; musculoskeletal pain, and; recurrent flu-like symptoms). The level of sickness behavior was similar between ME/CFS and chronic pain patients, and significantly higher than in patients from primary care and individuals from the general population (p’s <.001).

Conclusions: Symptoms in ME/CFS seem to present in distinct patterns, underlining the importance of the further study of symptom but also illness subtypes. However, factors other than criteria symptoms, such as experiential avoidance and cognitive fusion, are likely more accessible targets in behavior medicine treatment. The results from the ACT-based feasibility study indicate the utility of conceptualizing disability in ME/CFS from a modern learning theory perspective, and the ACT-based behavior medicine treatment format should be further investigated in randomized controlled studies. Finally, sickness behavior processes may guide future research in the differentiation of ME/CFS illness subtypes, as indicated by the level of subjective sickness behavior reported in ME/CFS which is equal to the level found when healthy human subjects are injected with bacterial endotoxin to cause transient sickness behavior in an experimental setting.