By Dr. Javier Rivera | Nov. 4, 2021 | Generalities

It is common to hear that this or that disease is a complex one. In reality, the complexity lies in the lack of knowledge we have of the pathogenic mechanisms that produce them, but when we get to know them better, diseases are no longer considered complex.

Not so long ago all rheumatic diseases were included under a single heading called «rheumatism», and any disease in which there was bone, muscle or joint pain was included in this bag.

When the different pathogenic mechanisms that cause these diseases were discovered, they were classified into different groups, such as inflammatory, autoimmune, degenerative or metabolic rheumatic diseases, among the best known.

However, there is still a disease (or, rather, a group of them), represented by fibromyalgia, which resists being classified under a specific heading and this is because its pathogenic mechanisms have only recently begun to be understood. As a consequence, fibromyalgia has come a long way from when it first became known until the present day.

Fibromyalgia has been known for a long time, and the first idea was that it was a problem of hysteria exclusive to some unbalanced women.

In the 1960s, people began to believe that the disease was a consequence of the psychiatric disorders that the patient previously had, and the term psychogenic rheumatism came to be used; that is, a rheumatic disease caused by the psychopathological alterations of the patient. This concept was somewhat softer than the one mentioned before, but it is still in the same line.

Around the 1990s, it began to be seen that the most striking symptom, which is pain, is due to an alteration in the mechanisms of the nervous system that regulate pain, demonstrating that various structures, such as nerves, nerve pathways or brain nuclei were altered and could explain the origin of the pain. From then on, fibromyalgia began to be considered a chronic pain disease and a specific epigraph was created with this name where all those diseases that cause chronic pain were grouped, whatever their location.

For information purposes, it is estimated that between 10% and 20% of the general population suffer from any type of chronic pain, so the heading «Chronic Pain» is too broad and impractical when classifying these diseases.

However, in fibromyalgia patients have other frequent symptoms, which in some cases are even more important than the pain itself. Thus, fatigue, sleep disturbances, cognitive disorders, digestive problems, heart problems, anxiety or depressive symptoms are part of the disease. Therefore, it is not only a chronic pain disease, but it seems that it is much more than that.

On the other hand, other diseases or syndromes that cause chronic pain such as irritable bowel, dizziness, headaches, migraines, bruxism, jaw joint disorders or irritable bladder, very often accompany fibromyalgia and other related syndromes such as chronic fatigue or myalgic encephalomyelitis.

Thus, it seems that fibromyalgia is something more than a chronic pain syndrome, it is a disease with many symptoms -among which is chronic pain- and, therefore, we must find another more satisfactory explanation to understand and classify these diseases.

Several recent studies have shown that there is an inflammation problem in the brain of patients with fibromyalgia that could successfully explain the pain and also the other accompanying symptoms. For example, with some special magnetic resosance techniques in people with fibromyalgia, many hyperactivated brain areas have been observed that are not seen in healthy people. Also, several alterations have been seen that affect multiple molecules involved in the functioning of the nervous system, such as cytokines, neurotransmitters or inflammatory peptides that can explain the symptoms. Therefore, there are currently data suggesting that fibromyalgia could be a chronic inflammatory disease of the nervous system, a process of neuroinflammation.

Finally, due to the COVID pandemic, a new door has opened to understand the pathogenic mechanisms of fibromyalgia. Some patients, after having passed COVID, are left with a residual condition with multiple symptoms that is highly reminiscent of fibromyalgia and chronic fatigue syndrome. As COVID is produced by an infectious process that causes a severe inflammatory condition and is subsequently accompanied by an added autoimmunity phenomenon, the possibility that any of these mechanisms is acting in patients with fibromyalgia is feasible and should be taken into consideration when it comes to understanding this disease.

As we can see, the path that fibromyalgia has followed to this day has been long and has not ended yet. It is important to know how this trajectory has evolved so as not to be anchored in old concepts, and always have an open mind to future discoveries that will occur and that will shed more light on this disease.

(This article is a brief summary of the presentation «News in the diagnosis and classification of fibromyalgia: expectations and reflections», held at the last Annual Meeting of the Spanish Society of Rheumatology, 2021).