Fibromyalgia is a common and, to some extent, poorly understood condition that causes significant disability and therefore has major societal implications. The definition of the condition has varied throughout history, and today’s criteria differ significantly from those many doctors were trained in. Since the condition is so common, it is naturally important that doctors stay up to date on the diagnosis and treatment options.
Fibromylgia (FM) has long been a controversial diagnosis that has caused considerable confusion [1]. This has resulted in at least four new sets of diagnostic criteria over the past 10 years [2]. This lack of clarity and disagreement has been detrimental to patients and has led to the condition being viewed with skepticism by many physicians [3]. Fibromyalgia has also been understood and defined differently throughout history [4]. Unexplained pain has been known throughout the ages as a part of life and is described in historical sources from antiquity, where it was interpreted as a symptom of the gods’ wrath. There has been greater understanding of obvious connections, such as the link between having an arrow in the shoulder and feeling pain [5].
Background and history
In 1592, the French physician Guillaume de Baillou used the term “rheumatism” to describe what we today refer to as fibromyalgia, that is, “muscle pain not resulting from any known injury.” In 1816, the Scottish surgeon William Balfour demonstrated that these patients were highly sensitive to mechanical pressure in certain areas, so-called “tender points.” Later, in the 1880s, the French physician François Valleix claimed that these tender points together formed neural systems that caused widespread pain in the body. In 1904, the neurologist William Gowers gained acceptance for viewing the condition as an inflammatory rheumatic disease and called it “fibrositis” [6]. This narrative persisted for a long time and led to fibromyalgia traditionally being managed by rheumatologists. Hugh Smythe eventually laid the foundation for modern fibromyalgia research. In 1972, he defined the phenotype of fibromyalgia as a condition with both widespread pain and tender points as essential characteristics. In 1976, the term “fibrositis” was changed to “fibromyalgia” following a paradigm shift [7], and was thus no longer understood as an inflammatory condition.
The debate over criteria later resulted in a consensus with the so-called ACR 1990 criteria. These “American College of Rheumatology” criteria defined fibromyalgia as chronic, widespread pain of unknown cause with at least 11 of 18 tender points measured by a thumb pressure of less than 4 kg/cm² [8]. The ACR 1990 criteria worked for a while and were accepted for many years, but from around the turn of the millennium, they came under increasing criticism, both in clinical practice and research. They were therefore gradually phased out. It turned out that doctors did not understand how to properly examine the tender points; they measured them very inconsistently or refused to do so. In addition, the tender points were most often interpreted as muscle damage, whereas modern research has instead concluded that the pain is caused by functional changes in the pain regulation systems of the CNS and the peripheral nervous system. Another limitation of the old 1990 ACR criteria was that they ignored symptoms other than pain, such as fatigue, sleep disturbances, memory problems, headaches, irritable bowel syndrome, frequent urination, and depressive symptoms. They also did not scale the severity of FM symptoms. Consequently, it was difficult to measure “how much” fibromyalgia a person had. Nor was it possible to evaluate changes over time.
The old ACR1990 criteria also defined fibromyalgia as a diagnosis of exclusion, whereas the requirement that the patient could not have other conditions that could explain the pain was removed in the 2016 criteria. It is now agreed that other diagnoses can coexist with fibromyalgia, such as arthritis, ankylosing spondylitis, migraine, and others.
Fibromyalgia was previously classified as a musculoskeletal condition in ICD-10. This classification has now been abandoned with the introduction of the term “primary pain” in ICD-11 from 2015 [9]. “Primary pain” refers to “pain as a disease in itself without a definite etiology,” that is, a condition without a primary musculoskeletal etiology [9]. It is, incidentally, problematic that the ICPC and ICD classify fibromyalgia differently, but comparative studies have been conducted that allow them to be used interchangeably [10]. The International Association for the Study of Pain (IASP) divides pain into three main categories: nociceptive (pain caused by tissue damage), neuropathic (pain caused by structural nerve damage), and so-called “nociplastic” pain [11], that is, functional changes in the neurogenic pain systems. Fibromyalgia is considered a nociplastic pain condition. Pain in fibromyalgia is widespread, is often described as burning, and frequently moves around. The pain must last for at least 3 months and be accompanied by other symptoms such as fatigue, sleep problems (not waking up rested in the morning), difficulty concentrating and memory problems (“brain fog”), irritable bowel syndrome, headaches, and periods of depressive symptoms. Mechanical tenderness or tender points are no longer measured.
Diagnosis
In 2016, the criteria for fibromyalgia were revised again, and these are the criteria currently in use [12]. To reach a diagnosis, the patient must complete a questionnaire in consultation with a doctor to assess the distribution of pain and six comorbid symptoms. This results in the “fibromyalgia score” (FS). The doctor also reviews other relevant background information and medical history. With the new ACR 2016 criteria, the patient can now rate widespread pain on a graded scale or index (“widespread pain index”) from 0 to 19, as well as other symptoms (symptom score scale (SSS) from 0 to 12, which is summed to a total of 0–31 “Fibromyalgia Score” in a questionnaire. This allows fibromyalgia to be categorized by intensity: Mild, Moderate, Severe, or Very Severe fibromyalgia.
The figure shows how fibromyalgia can now be graded based on the “Fibromyalgia Score” (FS), also called the “polysymptomatic distress score” (PDS).
Here’s how fibromyalgia is scored now:
1. Pain must be present in at least 7 of 19 body regions (“widespread pain index” or WPI ≥7). In addition, the symptom scale score (SSS) must be at least 5 out of 12 points (SSS score ≥5). [Alternatively, WPI = 4–6 with an SSS score ≥9].
2. The pain must be widespread; defined as pain in at least four of five regions (left/right upper quadrants, left/right lower quadrants, and neck/spine).
3. Symptoms must have been stable for at least 3 months.
Examples of how to complete the questionnaire used to diagnose fibromyalgia; see the text for an explanation.
The sum of WPI + SSS is thus called the fibromyalgia score (FS), but also the so-called “polysymptomatic distress score” (PDS) because it can be used generically for other conditions such as CFSME, cancer following chemotherapy, radiation therapy, and surgery, post-COVID-19, and PTSD [13]. It is worth noting that there is no absolute fibromyalgia cutoff on the FS score. Fibromyalgia is diagnosed only if criteria 1, 2, and 3 (see above) are met. For example, one might have a case where WPI = 8, SSS = 5, and thus FS (PDS) = 13, while the number of pain regions is only 3 out of 5; therefore, the patient does not have fibromyalgia (Example 1), whereas the same FS score could have resulted in a fibromyalgia diagnosis if the pain had been present in >3 regions. The patient in Example 2 scores WPI = 10, SSS = 6, pain is present in all regions (5/5), and the symptoms have persisted for at least 3 months. This patient therefore has fibromyalgia with an FS score = 16 (i.e., “moderate,” bordering on mild).
A link to the validated fibromyalgia questionnaire with scoring manual can be found here:
The new 2016 criteria can be used in both research and clinical diagnosis in the doctor’s office, and have been validated and quality-assured in Norwegian [2]. This means they are comparable to the old fibromyalgia criteria from 1990 and should be used in their place, even though there are some nuances. In a similar clinical sample, fibromyalgia patients assessed using the ACR1990 criteria had a lower prevalence than those assessed using the ACR2016 criteria, and the ACR1990 criteria did not distinguish between “case and control” for anxiety/depression symptoms, whereas the ACR2016 criteria did [14]. The 2016 criteria are therefore a better tool for identifying cases of fibromyalgia in clinical practice and research. The 2016 criteria also capture symptoms other than pain and grade fibromyalgia on a continuous scale, not “either–or” as mentioned above. Incidentally, the female-to-male ratio is lower when using the 2016 criteria than with the 1990 criteria, having actually decreased from 9:1 to 2:1 [15–17]. The prevalence of fibromyalgia is generally estimated to be 2–4% [16], but up to 35–40% when associated with, for example, ankylosing spondylitis [18] or rheumatoid arthritis [19].
Causes and Mechanisms
Prior to the introduction of the new diagnostic criteria and forms, there has been a shift in the understanding of the underlying mechanisms of fibromyalgia. Patients sometimes report that some doctors claim that “fibromyalgia does not exist” or is merely a catch-all term for “everything that is difficult,” and that there is no help available for it. The International Association for the Study of Pain (IASP), however, believes that fibromyalgia is a real and significant condition, and is highlighting it as one of the main themes of the upcoming European pain conference EFIC2025 in Lyon. Fibromyalgia is classified as the prototype of so-called nocipathic pain, i.e., pain caused by functional changes in peripheral pain receptors as well as in the pain regulation systems of the CNS [20]. The condition should be treated symptomatically, similar to structural nerve damage pain, with biopsychosocial pain management and, if necessary, rehabilitation in the most severe cases. Fibromyalgia is not a primary muscle disorder, nor is it an inflammatory rheumatological disease. The main hypotheses regarding its cause are linked to genetics, epigenetics, lifestyle, trauma, and immunology. Polli and colleagues have summarized the relationship between these factors in a model, in which genetics cause epigenetic changes moderated by lifestyle and environmental factors—which in turn lead to systemic responses involving cortisol release as well as neurogenic and immunological system responses [21]. The trauma theory is well-established, particularly regarding abuse and maltreatment in childhood [22], sexual and other physical abuse, medical trauma, accidents, emotional abuse, and other life-course traumas [23], as well as war trauma [24]. It is clear that immunological mechanisms also play a role, but it is difficult to gain a clear overview here. In 2021, Goebel and colleagues published an article that attracted attention. It showed that it was possible to transfer fibromyalgia symptoms from humans to mice by injecting antibodies from fibromyalgia patients [25, 26].
A note on treatment
Many general practitioners have likely felt helpless when dealing with this patient group and have had few tools at their disposal. The situation has not been improved by the fact that, as a general rule, fibromyalgia cannot be referred for further treatment, since these patients do not have access to specialist healthcare services, such as rheumatology departments. A principle in the modern management of fibromyalgia is that diagnosis and treatment are graded. As mentioned under “diagnosis,” the “case” versus “non-case” paradigm no longer applies; instead, fibromyalgia should be scaled from mild to very pronounced/severe. Treatment also follows the principle of grading. There are recommendations from the European League Against Rheumatism (EULAR) [27] and a short version in Norwegian: https://www.diakonhjemmetsykehus.no/498d3c/siteassets/seksjon/nkrr/documents/eularoppsum_anbefaltbehandling-fibromyalgi_2019.pdf
In Norway, several interesting projects are underway for the treatment of fibromyalgia in general practice. One such example is the “Nomed Project” at St. Olav’s Hospital, discussed in the latest issue of Utposten, No. 5, 2024. Cathrine Abrahamsen’s ICIT project has also been previously discussed in Utposten (23). It is also worth mentioning the back pain project led by general practitioner, researcher, and AFU fellow at the University of Oslo (UiO) Andreas Pahle, who uses “Pain Reprocessing Therapy” in treatment. Currently, these projects are in the initial phase.
Internationally, the following non-pharmacological interventions are best documented for fibromyalgia: Aerobic (subthreshold) exercise, psychoeducation, sleep hygiene, and cognitive behavioral therapy (various types, including ACT), stress management, “mind-body” exercises, and more [28]. In many municipalities, local treatment services are also being expanded, often organized under healthy living centers. It is still possible to refer fibromyalgia/chronic pain patients to rehabilitation, for example: https://unicare.no/coperio/vare-klinikker/trondheim/.
There is also value in pharmacological treatment. In such cases, this serves as a supplement to non-pharmacological interventions. In pharmacological pain management, it is important to remember that since fibromyalgia pain is nocipathic or phenotypically neuropathic—similar to, for example, diabetic neuropathy—medications used for neuropathic pain must be employed. NSAIDs and acetaminophen have no place in the treatment of fibromyalgia per se, but may be used if other pain conditions are present (e.g., soft tissue injuries, enthesopathies, osteoarthritis, inflammatory rheumatic disorders, and others). The following medications are recommended for fibromyalgia:
Duloxetine (Cymbalta), amitriptyline (Sarotex), or possibly pregabalin (Lyrica), gabapentin (Neuronin), nortriptyline (Noritren), and low-dose naltrexone (LDN). Opioids are not recommended! See details and dosages in the fibromyalgia brochure for healthcare professionals: https://fibromyalgi.no/wp-content/uploads/2023/12/Fibromyalgi_NTNU_brosjyre_A5_web-1.pdf
Amitriptyline and duloxetine can be prescribed on a blue prescription under certain conditions. In such cases, it is a requirement that a TCA such as amitriptyline be tried first, which is illogical given that duloxetine is considered a first-line treatment. It is also possible to prescribe gabapentin on a blue prescription, while pregabalin requires an application—and a requirement here is that gabapentin has been tried first.
Social Security and NAV
When writing a medical certificate for NAV regarding a patient with fibromyalgia, it is important to remember that “in cases with a lack of objective findings, greater documentation requirements apply.” A comprehensive functional assessment from a biopsychosocial perspective is particularly important. Treatment for fibromyalgia is interdisciplinary and complex, and therefore often challenging to explain.
Here is a link to the sick leave guide for fibromyalgia (HDir): https://www.helsedirektoratet.no/veiledere/sykmelderveileder
The guide for physicians provides useful advice on questions regarding sick leave for patients with fibromyalgia.
References:
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2. Fors, E.A., et al., Fibromyalgia 2016 criteria and assessments: comprehensive validation in a Norwegian population. Scand J Pain, 2020.
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5. Fors, E.A., Hva er smerte. 2012, Oslo: Universitetsforlaget.
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12. Wolfe, F., et al., 2016 Revisions to the 2010/2011 fibromyalgia diagnostic criteria. Semin Arthritis Rheum, 2016. 46(3): p. 319-329.
13. Upadhyaya, S.K., et al., Fibromyalgia and mental health in rheumatoid arthritis: a cross-sectional prevalence study from the COVID-19 pandemic. BMJ Open, 2023. 13(6): p. e069014.
14. Fors, E.A., K.-A. Wensaas, and A.-S. Helvik, Prevalence and characteristics of fibromyalgia according to three fibromyalgia diagnostic criteria: A secondary analysis study. Scandinavian Journal of Pain, 2024. 24(1).
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17. Arout, C.A., et al., Gender Differences in the Prevalence of Fibromyalgia and in Concomitant Medical and Psychiatric Disorders: A National Veterans Health Administration Study. J Womens Health (Larchmt), 2018. 27(8): p. 1035-1044.
18. Shapoval, I. and M. Stanislavchuk, Comparative characteristics of ACR 1990, mACR 2010, ACR 2016 and AAPT 2019 criteria for diagnosing fibromyalgia in patients with ankylosing spondylitis. Rheumatol Int, 2022.
19. El-Kasmi, H., et al., The Prevalence of Fibromyalgia in Rheumatoid Arthritis Patients Using the Fibromyalgia Assessment Screening Tool (FAST 4) Based on the Multidimensional Health Assessment Questionnaire (MDHAQ). Cureus, 2024. 16(7): p. e64011.
20. Clauw, D.J., From fibrositis to fibromyalgia to nociplastic pain: how rheumatology helped get us here and where do we go from here? Ann Rheum Dis, 2024.
21. Polli, A., et al., Linking Lifestyle Factors to Complex Pain States: 3 Reasons Why Understanding Epigenetics May Improve the Delivery of Patient-Centered Care. J Orthop Sports Phys Ther, 2019. 49(10): p. 683-687.
22. Vera Cruz, G., et al., Machine learning reveals the most important psychological and social variables predicting the differential diagnosis of rheumatic and musculoskeletal diseases. Rheumatol Int, 2022. 42(6): p. 1053-1062.
23. Kaleycheva, N., et al., The role of lifetime stressors in adult fibromyalgia: systematic review and meta-analysis of case-control studies. Psychol Med, 2021. 51(2): p. 177-193.
24. Lawrence-Wolff, K.M., et al., Prevalence of Fibromyalgia Syndrome in Active-Duty Military Personnel. Arthritis Care Res (Hoboken), 2023. 75(3): p. 667-673.
25. Goebel, A., et al., Passive transfer of fibromyalgia symptoms from patients to mice. J Clin Invest, 2021. 131(13).
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egil.a.fors@ntnu.no
