system, but the nervous system can also affect the gut. Neurological effects mediated via the autonomic nervous system as well as the hypothalamic pituitary adrenal axis are directed to intestinal functional effector cells, which in turn are under the influence of the gut microbiota. Gut-brain axis The gut-brain axis, which connects the gut microbiome to the brain via the enteric nervous system, is another area of research. Fibromyalgia patients have less varied gut flora and altered serum metabolome levels of glutamate and serine, implying abnormalities in neurotransmitter metabolism. Diagnosis There is no single pathological feature, laboratory finding, or biomarker that can diagnose fibromyalgia and there is debate over what should be considered diagnostic criteria and whether an objective diagnosis is possible. In most cases, people with fibromyalgia symptoms may have laboratory test results that appear normal and many of their symptoms may mimic those of other rheumatic conditions such as arthritis or osteoporosis. The specific diagnostic criteria for fibromyalgia have evolved over time. American College of Rheumatology 1990 The first widely accepted set of classification criteria for research purposes was elaborated in 1990 by the Multicenter Criteria Committee of the American College of Rheumatology. These criteria, which are known informally as "the ACR 1990", defined fibromyalgia according to the presence of the following criteria: A history of widespread pain lasting more than three months – affecting all four quadrants of the body, i.e., both sides, and above and below the waist. Tender points – there are 18 designated possible tender points (although a person with the disorder may feel pain in other areas as well). The ACR criteria for the classification of patients were originally established as inclusion criteria for research purposes and were not intended for clinical diagnosis but have later become the de facto diagnostic criteria in the clinical setting. A controversial study was done by a legal team looking to prove their client's disability based primarily on tender points and their widespread presence in non-litigious communities prompted the lead author of the ACR criteria to question now the useful validity of tender points in diagnosis. Use of control points has been used to cast doubt on whether a person has fibromyalgia, and to claim the person is malingering. American College of Rheumatology 2010 provisional criteria In 2010, the American College of Rheumatology approved provisional revised diagnostic criteria for fibromyalgia that eliminated the 1990 criteria's reliance on tender