Fibromyalgia is characterized by diffuse musculoskeletal pain, fatigue, poor sleep, and other somatic symptoms.¹ Chronic diffuse pain affects 10% to 15% of adults in the general population worldwide, many of whom have fibromyalgia.^2,3 Approximately 2% of people in the United States have fibromyalgia, although the prevalence varies across populations and with the diagnostic criteria used.³ Fibromyalgia can occur in children and adults and is found worldwide and across cultures. Women are diagnosed more frequently than men; a Scottish survey found that women are diagnosed between two and 14 times as often as men depending on the criteria used.^3,4 Changes in the diagnostic criteria over the past decade, including the elimination of specific tender points, have resulted in more patients with chronic pain meeting the criteria for fibromyalgia.^3–5

Pathophysiology

Fibromyalgia is likely caused by disordered central nociceptive signal processing that leads to sensitization expressed as hyperalgesia and allodynia, which is similar to chronic pain conditions such as irritable bowel syndrome, interstitial cystitis, chronic pelvic pain, and chronic low back pain.^6,7 Functional brain imaging suggests that this aberrant processing may be attributed to an imbalance between excitatory and inhibitory neurotransmitters, particularly within the insula.⁸ Suggested etiologies include dysfunction of the hypothalamic-pituitary-adrenal axis and the autonomic nervous system, diffuse inflammation, glial cell activation, small fiber neuropathy, and infections such as the Epstein-Barr virus, Lyme disease, and viral hepatitis.⁹ Twin studies suggest a genetic component may also be a factor.¹⁰

Clinical Presentation

Chronic diffuse pain is the predominant symptom in most patients with fibromyalgia. Patients may also experience muscle stiffness and tenderness. The physical examination in patients with fibromyalgia generally finds diffuse tenderness without other unusual findings. If joint swelling, inflammation, or deformities are present, an alternative or additional diagnosis should be investigated.⁵ Fatigue and sleep disturbances are also common.^5,11 Sleep disturbances include difficulty falling and staying asleep, frequent awakenings, or feeling unrefreshed after sleeping. Comorbid mental health diagnoses are common, as are cognitive symptoms such as poor concentration, forgetfulness, or altered thinking.^5,6,12 This cognitive dysfunction has been termed “fibrofog” and is described by patients as a mental slowing that adversely affects daily activities.¹³

The presence of another painful disorder does not exclude the diagnosis of fibromyalgia. The Fibromyalgia Rapid Screening Tool can screen patients with diffuse chronic pain to help distinguish between fibromyalgia and other conditions (Table 1).¹⁴ The tool may also be used to detect coexisting fibromyalgia in patients with confirmed rheumatologic conditions.¹⁵

Diagnosis

Fibromyalgia should be considered in patients with chronic pain without a history of tissue injury or inflammation that has been present for more than three months and who also have fatigue, mood issues, and sleep disturbances.

Multiple diagnostic criteria for fibromyalgia have been developed, many of which are in use today. The initial American College of Rheumatology (ACR) classification criteria included widespread pain and multiple specific muscular tender points.¹⁶ When these criteria were updated in 2010 and 2011, the physical examination of tender points was eliminated, and a symptom severity scale and self-reported widespread pain index were added.¹¹ The 2011 changes were updated in 2016 to require generalized pain in at least four of five regions for at least three months.¹¹ The 2016 criteria also require minimum scores on the widespread pain index and the symptom severity scale, which rates the degree of fatigue, waking unrefreshed, and cognitive symptoms.