Association of circulating biomarkers with illness severity measures differentiates myalgic encephalomyelitis/chronic fatigue syndrome and post-COVID-19 condition: a prospective pilot cohort study.

BACKGROUND: Accumulating evidence suggests that autonomic dysfunction and persistent systemic inflammation are common clinical features in myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID. However, there is limited knowledge regarding their potential association with circulating biomarkers and illness severity in these conditions. METHODS: This single-site, prospective, cross-sectional, pilot cohort study aimed to distinguish between the two patient populations by using self-reported outcome measures and circulating biomarkers of endothelial function and systemic inflammation status. Thirty-one individuals with ME/CFS, 23 individuals with long COVID, and 31 matched sedentary healthy controls were included. All study participants underwent non-invasive cardiovascular hemodynamic challenge testing (10 min NASA lean test) for assessment of orthostatic intolerance. Regression analysis was used to examine associations between outcome measures and circulating biomarkers in the study participants. Classification across groups was based on principal component and discriminant analyses. RESULTS: Four ME/CFS patients (13%), 1 with long COVID (4%), and 1 healthy control (3%) presented postural orthostatic tachycardia syndrome (POTS) using the 10-min NASA lean test. Compared with matched healthy controls, ME/CFS and long COVID subjects showed higher levels of ET-1 (p < 0.05) and VCAM-1 (p < 0.001), and lower levels of nitrites (NOx assessed as NO2- + NO3-) (p < 0.01). ME/CFS patients also showed higher levels of serpin E1 (PAI-1) and E-selectin than did both long COVID and matched control subjects (p < 0.01 in all cases). Long COVID patients had lower TSP-1 levels than did ME/CFS patients and matched sedentary healthy controls (p < 0.001). As for inflammation biomarkers, both long COVID and ME/CFS subjects had higher levels of TNF-α than did matched healthy controls (p < 0.01 in both comparisons). Compared with controls, ME/CFS patients had higher levels of IL-1ß (p < 0.001), IL-4 (p < 0.001), IL-6 (p < 0.01), IL-10 (p < 0.001), IP-10 (p < 0.05), and leptin (p < 0.001). Principal component analysis supported differentiation between groups based on self-reported outcome measures and biomarkers of endothelial function and inflammatory status in the study population. CONCLUSIONS: Our findings revealed that combining biomarkers of endothelial dysfunction and inflammation with outcome measures differentiate ME/CFS and Long COVID using robust discriminant analysis of principal components. Further research is needed to provide a more comprehensive characterization of these underlying pathomechanisms, which could be promising targets for therapeutic and preventive strategies in these conditions.

Myalgic encephalomyelitis/chronic fatigue syndrome from current evidence to new diagnostic perspectives through skeletal muscle and metabolic disturbances.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a demanding medical condition for patients and society. It has raised much more public awareness after the COVID-19 pandemic since ME/CFS and long-COVID patients share many clinical symptoms such as debilitating chronic fatigue. However, unlike long COVID, the etiopathology of ME/CFS remains a mystery despite several decades' research. This review moves from pathophysiology of ME/CFS through the compelling evidence and most interesting hypotheses. It focuses on the pathophysiology of skeletal muscle by proposing the hypothesis that skeletal muscle tissue offers novel opportunities for diagnosis and treatment of this syndrome and that new evidence can help resolve the long-standing debate on terminology.

Management of severe ME/CFS in children and young people in the UK: a British Paediatric Surveillance Unit study.

OBJECTIVE: Severe myalgic encephalomyelitis or chronic fatigue syndrome (ME/CFS) in children and young people (CYP) is a little-understood condition which significantly impacts education, development and quality of life. We used data from a population-wide surveillance study to explore the screening investigation, referral and management of suspected cases of paediatric severe ME/CFS. METHODS: A British Paediatric Surveillance Unit (BPSU) study reported cases of CYP with suspected severe ME/CFS between February 2018 and February 2019. Paediatricians reporting cases to BPSU and allied healthcare professionals in two large specialist paediatric ME/CFS centres were invited to complete questionnaires for CYP meeting the surveillance case definition. The study focused primarily on CYP with confirmed severe ME/CFS and the extent to which their care met NICE (The National Institute for Health and Care Excellence) recommendations but also considered separately those with probable or possible severe ME/CFS. RESULTS: This study includes a total of 92 CYP with suspected severe ME/CFS; 33 meeting criteria for severe ME/CFS and an additional 59 classified as probable or possible severe ME/CFS. For 16 possible cases, incomplete investigation to exclude alternative diagnoses prevented confirmation of a severe ME/CFS diagnosis. Only 21 of 33 (64%) confirmed severe ME/CFS cases had been referred to specialist services. The management provided varied considerably between patients and four received nothing at all. Of the management provided, the most frequent approaches were medication (67%), activity management (61%) and physiotherapy (61%). Domiciliary assessments and support, and social services referrals were received by 12% and 6% of confirmed severe cases. Similar proportions of management approaches were seen in probable/possible severe ME/CFS. CONCLUSION: Full investigation is frequently incomplete in CYP with suspected severe ME/CFS and recommendations for referral and management are poorly implemented, in particular the needs of CYP who are unable to leave their home might be poorly met.

Fatigue and symptom-based clusters in post COVID-19 patients: a multicentre, prospective, observational cohort study.

BACKGROUND: In the Netherlands, the prevalence of post COVID-19 condition is estimated at 12.7% at 90-150 days after SARS-CoV-2 infection. This study aimed to determine the occurrence of fatigue and other symptoms, to assess how many patients meet the Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) criteria, to identify symptom-based clusters within the P4O2 COVID-19 cohort and to compare these clusters with clusters in a ME/CFS cohort. METHODS: In this multicentre, prospective, observational cohort in the Netherlands, 95 post COVID-19 patients aged 40-65 years were included. Data collection at 3-6 months after infection included demographics, medical history, questionnaires, and a medical examination. Follow-up assessments occurred 9-12 months later, where the same data were collected. Fatigue was determined with the Fatigue Severity Scale (FSS), a score of ≥ 4 means moderate to high fatigue. The frequency and severity of other symptoms and the percentage of patients that meet the ME/CFS criteria were assessed using the DePaul Symptom Questionnaire-2 (DSQ-2). A self-organizing map was used to visualize the clustering of patients based on severity and frequency of 79 symptoms. In a previous study, 337 Dutch ME/CFS patients were clustered based on their symptom scores. The symptom scores of post COVID-19 patients were applied to these clusters to examine whether the same or different clusters were found. RESULTS: According to the FSS, fatigue was reported by 75.9% of the patients at 3-6 months after infection and by 57.1% of the patients 9-12 months later. Post-exertional malaise, sleep disturbances, pain, and neurocognitive symptoms were also frequently reported, according to the DSQ-2. Over half of the patients (52.7%) met the Fukuda criteria for ME/CFS, while fewer patients met other ME/CFS definitions. Clustering revealed specific symptom patterns and showed that post COVID-19 patients occurred in 11 of the clusters that have been observed in the ME/CFS cohort, where 2 clusters had > 10 patients. CONCLUSIONS: This study shows persistent fatigue and diverse symptomatology in post COVID-19 patients, up to 12-18 months after SARS-CoV-2 infection. Clustering showed that post COVID-19 patients occurred in 11 of the clusters that have been observed in the ME/CFS cohort.

Joint Flexibility and Myalgic Encephalomyelitis/Chronic Fatigue Syndrome After Mononucleosis.

PURPOSE: Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic disease characterized by substantial fatigue, postexertional malaise, unrefreshing sleep, and orthostatic intolerance, among other symptoms. Specific risk factors for the development of ME/CFS have not been adequately characterized. It has been suggested that ME/CFS is a connective tissue disorder and that joint hyperflexibility is a risk factor for the development of ME/CFS. METHODS: The goal of this study was to examine whether joint hyperflexibility is a risk factor for the development of ME/CFS after infectious mononucleosis (IM). This study was part of a prospective cohort study. College students were studied for the development of IM and were followed up for the development of ME/CFS 6 months later. Participants in the cohort for the present study included 53 students who met criteria for ME/CFS 6 months after IM and 66 recovered control subjects who had modified Beighton scores (a measure of joint hyperflexibility) available. FINDINGS: No connection was found between joint hyperflexibility and the development of ME/CFS after IM. Differences in joint hyperflexibility (as measured by using the modified Beighton score) in the ME/CFS group and the control group were not statistically significant. Female subjects had significantly higher Beighton scores compared with male subjects. IMPLICATION: After IM, no relationship was found between joint hyperflexibility and the development of ME/CFS.

Lipid metabolism and functional somatic disorders in the general population. The DanFunD study.

OBJECTIVES: Earlier studies on the association between plasma lipid profiles and functional somatic disorders (FSD) are mainly small case control studies hampered by selection bias and do not consider the great overlap between the various FSDs. The aim of the present study was to investigate the associations between various FSDs and plasma lipid profiles (total cholesterol, HDL cholesterol, non-HDL cholesterol and triglycerides) in a large, unselected population. DESIGN: A cross-sectional general population-based study. SETTING: The Danish Study of Functional Somatic Disorders (DanFunD) conducted in 2011-2015 in 10 municipalities in the western part of greater Copenhagen, Denmark. PARTICIPANTS: A total of 8,608 men and women aged 18-76 years were included in the analyses. Various delimitations of FSD such as chronic fatigue, chronic widespread pain, irritable bowel, and bodily distress syndrome were measured using validated self-administrated questionnaires. Lipid parameters were measured from fasting plasma samples using colorimetric slide methods with Vitros 4600/5600 Ortho Clinical Diagnostics. OUTCOME MEASURES: Logistic regression analyses were used to calculate possible associations between plasma lipids and the various delimitations of FSD. Associations are presented by OR (95% CI) and shown in boxplots. RESULTS: We found a positive association between bodily distress syndrome and triglycerides and non-HDL cholesterol and a negative association with HDL-cholesterol, but no consistent association with total cholesterol. A similar pattern was observed for persons with chronic fatigue, and to some degree for persons with chronic widespread pain, whereas persons with irritable bowel did not show a clear association with the lipid profiles. CONCLUSION: This is the first major study on plasma lipid profiles and FSD indicating an association between some delimitations of FSD and an unfavorable lipid profile. Due to the cross-sectional design, it cannot be determined whether the findings are consequences or determinants of FSD. Further studies-preferable prospective studies-are needed.

Dry eye symptoms and signs in United States Gulf War era veterans with myalgic encephalomyelitis/chronic fatigue syndrome.

BACKGROUND: To examine ocular symptoms and signs of veterans with myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) diagnosis, ME/CFS symptoms, and controls. METHODS: This was a prospective, cross-sectional study of 124 South Florida veterans in active duty during the Gulf War era. Participants were recruited at an ophthalmology clinic at the Miami Veterans Affairs Hospital and evaluated for a diagnosis of ME/CFS, or symptoms of ME/CFS (intermediate fatigue, IF) using the Canadian Consensus criteria. Ocular symptoms were assessed via standardised questionnaires and signs via comprehensive slit lamp examination. Inflammatory blood markers were analysed and compared across groups. RESULTS: Mean age was 55.1 ± 4.7 years, 88.7% identified as male, 58.1% as White, and 39.5% as Hispanic. Ocular symptoms were more severe in the ME/CFS (n = 32) and IF (n = 48) groups compared to controls (n = 44) across dry eye (DE; Ocular Surface Disease Index [OSDI]: 48.9 ± 22.3 vs. 38.8 ± 23.3 vs. 19.1 ± 17.8, p < 0.001; 5 item Dry Eye Questionnaire [DEQ-5]: 10.8 ± 3.9 vs. 10.0 ± 4.6 vs. 6.6 ± 4.2, p < 0.001) and pain-specific questionnaires (Numerical Rating Scale 1-10 [NRS] right now: 2.4 ± 2.8 vs. 2.4 ± 2.9 vs 0.9 ± 1.5; p = 0.007; Neuropathic Pain Symptom Inventory modified for the Eye [NPSI-E]: 23.0 ± 18.6 vs. 19.8 ± 19.1 vs. 6.5 ± 9.0, p < 0.001). Ocular surface parameters and blood markers of inflammation were generally similar across groups. CONCLUSION: Individuals with ME/CFS report increased ocular pain but similar DE signs, suggesting that mechanisms beyond the ocular surface contribute to symptoms.

Catalytic Antibodies May Contribute to Demyelination in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome.

Here we report preliminary data demonstrating that some patients with myalgic encephalomyelitis/chronic fatiguesyndrome (ME/CFS) may have catalytic autoantibodies that cause the breakdown of myelin basic protein (MBP). We propose that these MBP-degradative antibodies are important to the pathophysiology of ME/CFS, particularly in the occurrence of white matter disease/demyelination. This is supported by magnetic resonance imagining studies that show these findings in patients with ME/CFS and could explain symptoms of nerve pain and muscle weakness. In this work, we performed a series of experiments on patient plasma samples where we isolated and characterized substrate-specific antibodies that digest MBP. We also tested glatiramer acetate (copaxone), an FDA approved immunomodulator to treat multiple sclerosis, and found that it inhibits ME/CFS antibody digestion of MBP. Furthermore, we found that aprotinin, which is a specific serine protease inhibitor, specifically prevents breakdown of MBP while the other classes of protease inhibitors had no effect. This coincides with the published literature describing catalytic antibodies as having serine protease-like activity. Postpandemic research has also provided several reports of demyelination in COVID-19. Because COVID-19 has been described as a trigger for ME/CFS, demyelination could play a bigger role in patient symptoms for those recently diagnosed with ME/CFS. Therefore, by studying proteolytic antibodies in ME/CFS, their target substrates, and inhibitors, a new mechanism of action could lead to better treatment and a possible cure for the disease.

Insomnia and sleep characteristics in post COVID-19 fatigue: A cross-sectional case-controlled study.

OBJECTIVE: Following COVID-19 many patients report persistent fatigue and insomnia. Given the overlapping features, insomnia can be underdiagnosed in post-COVID-19 fatigue patients. This study aimed to determine insomnia severity, prevalence of clinical insomnia and sleep characteristics of post-COVID-19 fatigue patients. Data of post-COVID-19 fatigue patients were compared with those of patients with chronic fatigue syndrome (ME/CFS), a condition resembling post-COVID-19 fatigue. METHODS: In this cross-sectional case-controlled study, insomnia severity, assessed with the Insomnia Severity Index (ISI), and prevalence of clinical insomnia (ISI score ≥ 10), were determined in patients with post-COVID-19 fatigue (n = 114) and compared with ME/CFS (n = 59) using ANCOVA and logistic regression, respectively. Linear regression analyses were used to evaluate whether mood, concentration problems, pain, fatigue (assessed with questionnaires) and diagnosis were associated with insomnia. Sleep characteristics were determined with a sleep diary and accelerometer in post-COVID-19 fatigue and compared with ME/CFS using ANCOVA. RESULTS: In patients with post-COVID-19 fatigue mean (SD) insomnia severity was 11.46 (5.7) and 64% reported clinical insomnia. Insomnia severity was significantly associated with depressive symptoms (ß = 0.49, p = 0.006) and age (ß = 0.08, p = 0.04). The mean (SD) subjective sleep duration was 7.4 (1.0) hours with a sleep efficiency of 82 (11)%. Several subjective sleep characteristics of the post-COVID-19 fatigue patients differed from ME/CFS patients; only sleep duration, being significantly shorter in post-COVID-19 fatigue patients (p = 0.003), seemed clinically relevant (d = 0.58). CONCLUSION: Insomnia severity and prevalence of clinical insomnia are high in patients with post-COVID-19 fatigue. Insomnia should be assessed and if present treated with insomnia focused therapy.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome in Adults: United States, 2021-2022.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a complex, multisystem illness characterized by activity-limiting fatigue, worsening of symptoms after activity, and other symptoms (1). It affects all age, sex, and racial and ethnic groups and costs the U.S. economy about $18-$51 billion annually (2-5). This report describes the percentage of adults who had ME/CFS at the time of interview by selected demographic and geographic characteristics based on data from the 2021-2022 National Health Interview Survey (NHIS).

Increased risk of chronic fatigue syndrome following infection: a 17-year population-based cohort study.

BACKGROUND: Previous serological studies have indicated an association between viruses and atypical pathogens and Chronic Fatigue Syndrome (CFS). This study aims to investigate the correlation between infections from common pathogens, including typical bacteria, and the subsequent risk of developing CFS. The analysis is based on data from Taiwan's National Health Insurance Research Database. METHODS: From 2000 to 2017, we included a total of 395,811 cases aged 20 years or older newly diagnosed with infection. The cases were matched 1:1 with controls using a propensity score and were followed up until diagnoses of CFS were made. RESULTS: The Cox proportional hazards regression analysis was used to estimate the relationship between infection and the subsequent risk of CFS. The incidence density rates among non-infection and infection population were 3.67 and 5.40 per 1000 person-years, respectively (adjusted hazard ratio [HR] = 1.5, with a 95% confidence interval [CI] 1.47-1.54). Patients infected with Varicella-zoster virus, Mycobacterium tuberculosis, Escherichia coli, Candida, Salmonella, Staphylococcus aureus and influenza virus had a significantly higher risk of CFS than those without these pathogens (p < 0.05). Patients taking doxycycline, azithromycin, moxifloxacin, levofloxacin, or ciprofloxacin had a significantly lower risk of CFS than patients in the corresponding control group (p < 0.05). CONCLUSION: Our population-based retrospective cohort study found that infection with common pathogens, including bacteria, viruses, is associated with an increased risk of developing CFS.

Post-COVID and ME/CFS - DoWe Need New Disease Theories?

Background and Research Question: The SARS-CoV-2 pandemic often resulted in prolonged illness courses. A particular challenge today lies in the clinical presentation resembling that of Myalgic Encephalitis/Chronic Fatigue Syndrome (ME/CFS). Method: We review selected literature concerning the psychosocial factors influencing chronic courses characterized primarily by fatigue. Additionally, we explore the neurobiologically grounded theory of "Predictive Coding" as a possible explanatory framework for complex somato- psychic interactions. Results: Physical findings only partially account for the dynamics and progression of chronic fatigue syndromes, necessitating more intricate disease models that incorporate aspects of bodily perception. Conclusions: Incorporating these newer theories of perception and behavior could provide a more helpful perspective on phenomena such as fatigue, leading to improved therapeutic support measures, all without contributing to premature attributions of "psychological" causes and the associated risk of stigmatization.

Pre-pandemic activity on a myalgic encephalomyelitis/chronic fatigue syndrome support forum is highly associated with later activity on a long COVID support forum for a variety of reasons: A mixed methods study.

Encephalomyelitis/chronic fatigue syndrome (ME/CFS) and long COVID share some clinical and social characteristics. We predicted that this would lead to an increased interaction between pre-pandemic members of an ME/CFS online support community and a long COVID community. We performed a mixed-methods retrospective observational study of the Reddit activity of 7,544 users active on Reddit's long COVID forum. From among 1600 forums, pre-pandemic activity specifically on a ME/CFS forum is the top predictor of later participation on the long COVID forum versus an acute COVID support forum. In the qualitative portion, motives for this co-participation included seeking mutual support and dual identification with both conditions. Some of this effect may be explained by pre-existing ME/CFS possibly being a risk factor for long COVID and/or SARS-CoV-2 infection being a cause of ME/CFS relapse. The high rate of ME/CFS patients seeking mutual support on a long COVID forum speaks to the long-suffering experience of these patients not feeling heard or respected, and the hope of some ME/CFS patients to gain legitimacy through the public's growing recognition of long COVID.

Understanding, diagnosing, and treating Myalgic encephalomyelitis/chronic fatigue syndrome - State of the art: Report of the 2nd international meeting at the Charité Fatigue Center.

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a devastating disease affecting millions of people worldwide. Due to the 2019 pandemic of coronavirus disease (COVID-19), we are facing a significant increase of ME/CFS prevalence. On May 11th to 12th, 2023, the second international ME/CFS conference of the Charité Fatigue Center was held in Berlin, Germany, focusing on pathomechanisms, diagnosis, and treatment. During the two-day conference, more than 100 researchers from various research fields met on-site and over 700 attendees participated online to discuss the state of the art and novel findings in this field. Key topics from the conference included: the role of the immune system, dysfunction of endothelial and autonomic nervous system, and viral reactivation. Furthermore, there were presentations on innovative diagnostic measures and assessments for this complex disease, cutting-edge treatment approaches, and clinical studies. Despite the increased public attention due to the COVID-19 pandemic, the subsequent rise of Long COVID-19 cases, and the rise of funding opportunities to unravel the pathomechanisms underlying ME/CFS, this severe disease remains highly underresearched. Future adequately funded research efforts are needed to further explore the disease etiology and to identify diagnostic markers and targeted therapies.

Long-term health outcomes of Q-fever fatigue syndrome patients.

This study determined long-term health outcomes (≥10 years) of Q-fever fatigue syndrome (QFS). Long-term complaints, health-related quality of life (HRQL), health status, energy level, fatigue, post-exertional malaise, anxiety, and depression were assessed. Outcomes and determinants were studied for the total sample and compared among age subgroups: young (<40years), middle-aged (≥40-<65years), and older (≥65years) patients. 368 QFS patients were included. Participants reported a median number of 12.0 long-term complaints. Their HRQL (median EQ-5D-5L index: 0.63) and health status (median EQ-VAS: 50.0) were low, their level of fatigue was high, and many experienced post-exertional malaise complaints (98.9%). Young and middle-aged patients reported worse health outcomes compared with older patients, with both groups reporting a significantly worse health status, higher fatigue levels and anxiety, and more post-exertional malaise complaints and middle-aged patients having a lower HRQL and a higher depression risk. Multivariate regression analyses confirmed that older age is associated with better outcomes, except for the number of health complaints. QFS has thus a considerable impact on patients' health more than 10 years after infection. Young and middle-aged patients experience more long-term health consequences compared with older patients. Tailored health care is recommended to provide optimalcare for each QFS patient.

A multicenter virome analysis of blood, feces, and saliva in myalgic encephalomyelitis/chronic fatigue syndrome.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is estimated to affect 0.4%-2.5% of the global population. Most cases are unexplained; however, some patients describe an antecedent viral infection or response to antiviral medications. We report here a multicenter study for the presence of viral nucleic acid in blood, feces, and saliva of patients with ME/CFS using polymerase chain reaction and high-throughput sequencing. We found no consistent group-specific differences other than a lower prevalence of anelloviruses in cases compared to healthy controls. Our findings suggest that future investigations into viral infections in ME/CFS should focus on adaptive immune responses rather than surveillance for viral gene products.

Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) and COVID-19: is there a connection?

OBJECTIVES: Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a chronic systemic disease that leads to neurological, immunological, autonomic, and energy metabolism dysfunction. COVID-19 has been reported to cause similar symptoms to ME/CFS. The study aims to investigate the prevalence of myalgic encephalomyelitis in patients post-COVID-19 infection by assessing acute and long-term COVID-19 symptoms. METHODS: A cross-sectional questionnaire was developed based on the ME/CFS diagnostic criteria, as specified by the IOM clinical diagnostic criteria, and administered to participants with confirmed COVID-19 who are more than 18 years old and have BMI below 40 Kg/m2. Data from 437 participants were completed. RESULTS: The current study results revealed that 8.1% of the study participants met the ME/CFS diagnostic criteria. Interestingly, 2.8 of the study participants were classified to have COVID-19 related to ME/CFS. While 4.6% of participants were determined to have disease-related fatigue, 0.7% of participants showed ME/CFS that was not related to COVID-19, and 3.7% of participants were considered to have long COVID-19. Almost one-fourth of the study participants had a family history of ME/CFS. The current study demonstrated that the prevalence of ME/CFS is similar to slightly higher than reported in the literature. CONCLUSION: The presence of a relationship between ME/CFS and COVID-19 has been supported by the results of our study. Follow-up of COVID-19 patients is strongly recommended to ensure proper management of ME/CFS symptoms.

Fatigue in Adults: Evaluation and Management.

Fatigue is among the top 10 reasons patients visit primary care offices, and it significantly affects patients' well-being and occupational safety. A comprehensive history and cardiopulmonary, neurologic, and skin examinations help guide the workup and diagnosis. Fatigue can be classified as physiologic, secondary, or chronic. Physiologic fatigue can be addressed by proper sleep hygiene, a healthy diet, and balancing energy expenditure. Secondary fatigue is improved by treating the underlying condition. Cognitive behavior therapy, exercise therapy, and acupuncture may help with some of the fatigue associated with chronic conditions. Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS) is a chronic, severe, and potentially debilitating disorder with demonstrated inflammatory, neurologic, immunologic, and metabolic abnormalities. ME/CFS has a poor prognosis, with no proven treatment or cure. It may become more common after the COVID-19 pandemic because many patients with long COVID (post-COVID-19 condition) have symptoms similar to ME/CFS. The most important symptom of ME/CFS is postexertional malaise. The 2015 National Academy of Medicine diagnostic criteria diagnose ME/CFS. Exercise can be harmful to patients with ME/CFS because it can trigger postexertional malaise. Patients should be educated about pacing their activity not to exceed their limited energy capacity. Treatment should prioritize comorbidities and symptoms based on severity.