Differences of research participants cognitive abilities pre- and post-illness onset are naturally variable and are difficult to measure because of a lack of specialized analytical tools that can consistently quantify the specific cognitive difficulties in CFS.The frequency of neuropsychiatric and neuropsychological symptoms is increased in the population of persons with CFS; the understanding of why this occurs is unresolved. Various hypotheses have been advanced to try to explain the relationship between the cognitive symptoms and the illness. Some researchers believe psychiatric causes underlie or contribute to the illness, while other researchers believe the illness causes biochemical and sociological changes in people that produce the symptoms. Cause
The cause of CFS is unknown. Genetic and physiological factors are thought to work together to precipitate and perpetuate the condition. A 2016 report by the Institute of Medicine states that CFS is a biologically based illness, but that the biologic abnormalities are not sensitive or specific enough to be useful as a diagnosis.Because it may begin as an influenza-like illness with a sudden onset, various infectious causes have been proposed, but evidence is insufficient to support such causation. Infections proposed include mononucleosis, Chlamydophila pneumoniae, human herpesvirus 6, and Lyme disease. Inflammation may be involved. Often, the illness will follow a viral illness such as mononucleosis or gastroenteritis. Risk factors
All ages, ethnic groups, and income levels are susceptible to the illness. The CDC states that Caucasians may be diagnosed more frequently than other races in America, but the illness is at least as prevalent among African Americans and Hispanics.
Hypothyroidism, anemia, coeliac disease (that can occur without gastrointestinal symptoms), diabetes and certain psychiatric disorders are a few of the diseases that must be ruled out if the patient presents with appropriate symptoms. Other diseases, listed by the Centers for Disease Control and Prevention, include infectious diseases (such as Epstein–Barr virus, influenza, HIV infection, tuberculosis, Lyme disease), neuroendocrine diseases (such as thyroiditis, Addisons disease, adrenal insufficiency, Cushings disease), hematologic diseases (such as occult malignancy, lymphoma), rheumatologic diseases (such as fibromyalgia, polymyalgia rheumatica, Sjögrens syndrome, lupus, giant-cell arteritis, polymyositis, dermatomyositis), psychiatric diseases (such as bipolar disorder, schizophrenia, delusional disorders, dementia, anorexia/bulimia nervosa), neuropsychologic diseases (such as obstructive sleep apnea, parkinsonism, multiple sclerosis), and others (such as nasal obstruction from allergies, sinusitis, anatomic obstruction, autoimmune diseases, cancer, chronic hepatitis, some chronic illness, alcohol or other substance abuse, pharmacologic side effects, heavy metal exposure and toxicity, marked body weight fluctuation). Ehlers–Danlos syndromes (EDS) may also have similar symptoms. Medications can also cause side effects that mimic symptoms of CFS.Persons with fibromyalgia (FM, or fibromyalgia syndrome, FMS), like those with CFS, have muscle pain, severe fatigue and sleep disturbances. The presence of allodynia (abnormal pain responses to mild stimulation) and of extensive tender points in specific locations differentiates FM from CFS, although the two diseases often co-occur.Depressive symptoms, if seen in CFS, may be differentially diagnosed from primary depression by the absence of anhedonia, decreased motivation, and guilt; and the presence of somatic symptoms such as sore throat, swollen lymph nodes, and exercise intolerance with post exertional exacerbation of symptoms.