Extended Abstract
1. Introduction
A Breakdown in the myelin’s neuronal brain cells in the central nervous system leads to generating Multiple Sclerosis (MS). The prevalence of MS in Iran is 40 per 100,000 people [1]. Recent research has identified environmental factors, such as stress, genetics, as well as immunological and microbiological matters, as the causes of this disease [4]. MS is categorized as an autoimmune disease, where the immune system attacks the brain and spinal cord and disrupts their functions [5]. 
 Studies have reported that psychological distress in these individuals is associated with biological changes [7]. A high rate of psychological problems has been reported in patients with MS [8, 9], which patients consider them as the cause of their pain [10]. 
Pain is an unpleasant feeling transmitted by the sensory neurons to the brain. However, pain falls beyond physical sensations or consciousness; Pain Perception (PP) also includes a mental interpretation of discomfort [12]. Therefore, PP involves the objective experience of physical processes and a mental experience, including affective-emotional characteristics [13]. Furthermore, distress, disease perception, fatigue, and cognitive-behavioral factors are associated with pain intensity and PP [14]. 
 Another common symptom that is commonly reported in MS patients is CFS. It is known as a specific problem, and decreases the quality of life of patients; however, the exact mechanism of it is unclear [15]. CFS is commonly associated with mild disease and may be the first symptom [16]. MS Council of Clinical Practice (1998) defined MS fatigue as “the lack of physical and psychological energy; i.e. experienced by the individuals or their caregivers and affects the individuals’ daily living activities” [20]. The study of MS, chronic fatigue, and PP suggests this disease is associated with many psychological problems for the patient. 
Therefore, studying the effectiveness of psychological interventions on the important mental variables of these patients is necessary. One of the beneficial psychological therapies in this regard can be Acceptance and Commitment Therapy (ACT) [26]. ACT is a mindfulness-based behavioral therapy. Reducing disease signs is not the purpose of ACT. In this therapy, the goal is to create a rich and meaningful life, while the patient accepts the inevitable suffering. 
 CFS and chronic pain are among the main causes of MS complications with cognitive and psychological dimensions. MS has not been treated conclusively, and most of the existing treatments only reduce symptoms or slow down the disease progression [1]. However, there is evidence of the usefulness of Cognitive Behavioral Therapy (CBT) in treating depression to cope with MS [29]. ACT is a modern approach, compared to CBT; i.e. used to improve one’s quality of life and ability to stay active and acting in accordance with their values [30]. Therefore, the present study aimed to explore the effectiveness of ACT on CFS and PP in people with MS. 

2. Methods
Thus, this was an applied and quasi-experimental research with a pre-test, post-test design. The statistical population includes all people with MS referring to the MS Society of Ahvaz. Thirty of these patients who were diagnosed with CFS by multidimensional fatigue inventory and whose condition was classified by a physician’s diagnosis according to the Expanded Disability Status Scale was poorly classified were selected as study samples. 

3. Results
Multivariable Analyze of Covariance (MANCOVA) was used to analyze the obtained data. Based on MANCOVA for PP and CFS scores, the results obtained from the Wilks Lambda test were at %95 confidence level (F=0.77, P<0.02). Thus, the two groups significantly differed in terms of at least one of the dependent variables (Table 1). 
Wilks Lambda’s test results of PP were significant for the subscales of sensory of pain perception, emotional perception of pain, and various pain perception (P≤0.05, F=5.70) (Table 2). The difference between the two groups in the sensory of pain perception (F=14.17, P<0.001), assessment of pain perception (F=10.54, P≤0.003), and various perceptions of pain (F=105.224, P≤0/05) was significant. 

4. Discussion
The study results indicated that ACT could reduce fatigue, and PP in patients with MS. ACT helps patients to experience their inner experience as a thought, and instead of responding to them, follow their values in life and things that matter to them. 
According to ACT, CFS, and PP in MS patients are due to their beliefs that their fatigue and pain are directly related to their illness. Furthermore, because they are unable to control their fatigue and pain, they try to avoid further activities. As a result, the patients fall in a defective loop and strengthen fatigue and distress. The current treatment, by breaking this faulty cycle, attempted to reduce fatigue and pain in MS patients. 
Ethical Considerations
Compliance with ethical guidelines
This study has an ethical approval (code: IR.IAU.KAU.REC.1397.029) and is a registered clinical trial (code: IRCT20181124041742N1). Before collecting data, ethical principles were considered which include: obtaining informed consent from participants, explaining the study objective and method to them, making them assured of the confidentiality of information, and having the right to leave the study at any time.
Funding
The present research was extracted from a master thesis approved by Maryam Davoodi in the Faculty of Letters and Humanities, Department of General Psychology at Salman Farsi University of Kazerun.
Authors contributions
Conceptualization, validation and project administration by all authors; methodology, investigation, resources and initial draft preparation by Maryam Davoodi; data analysis, editing and review by Leila Shameli. 
Conflicts of interest
The authors declared no conflicts of interest. 
Acknowledgements