Fibromyalgia

Fibromyalgia is characterised by widespread pain, fatigue, waking unrefreshed and cognitive disorders. It is usually a lifelong disorder. It is the prototypical centralised pain state where there is a fundamental problem with augmented pain or sensory processing and manifests in different parts of the body over time. While mental health complaints are common, the pain itself is not psychosomatic in nature.
==Epidemiology==
Fibromyalgia is present across the world, and has a prevalence ranging between 2% to 4%. It is the second most common rheumatological disorder after osteoarthritis. 10-15% of the population have chronic widespread pain, and there is no clear boundary separating those that have chronic widespread pain from those that have fibromyalgia. 
The peak onset is 20-50 but it can occur at any age. and is about twice as common in women. In clinical practice it is predominantly diagnosed in women in late middle age. Other risk factors are increasing age, family history of chronic pain, obesity, and poor mental and/or physical health. It occurs in all countries and ethnicities.
==Natural History==
Patients with fibromyalgia have roughly double the healthcare utilization compared to matched controls for at least a decade prior to diagnosis. Visits increase rapidly three years prior to diagnosis, then slightly decline after diagnosis, and rise again three years post-diagnosis, remaining at levels comparable to diagnosis but never reaching the level of two years prior to diagnosis. The overall benefit of the diagnostic process and medical input appears questionable at the population level.
Nearly all patients that are eventually diagnosed with fibromyalgia have a long history of having bouts of chronic regional pain various body regions over their lifetime dating back to adolescence. The most common reasons for clinical visits to GPs in order of frequency are depression, fatigue, chest pain, headache, sleep disturbance, dizziness, and IBS.
==Risk Factors==
There is often a strong familial predisposition to pain. Twin studies show that the risk of developing fibromyalgia is 50% genetic and 50% environmental. First degree relatives are more than 8 times as likely to also have fibromyalgia compared to controls. Many of the genes discovered thus far are involved in the regulation of neurotransmitters that modulate pain sensitivity, but genetic studies are not universally consistent and pain sensitivity is polygenic.
Psychological and other stressors are often a factor in the development and maintenance of the disorder, with the presence of sympathetic dysfunction, however it is not a psychosomatic condition. Environmental stressors are often identified, particularly those where there is acute pain that lasts a few weeks. For example motor vehicle accidents or certain infections.
Fibromyalgia is frequently observed as a comorbidity in other chronic pain conditions such as OA, RA, and lupus. About 15-30% of individuals with these rheumatic disorders meet FM criteria, and more individuals do not meet the criteria but display some FM elements, indicating the presence of pathophysiological abnormalities in CNS pain processing. The term "centralized pain" rather than "central sensitisation" is preferred when CNS factors play a significant role in magnifying pain and leading to other somatic symptoms.
== Pathophysiology ==
The current accepted hypothesis is that fibromyalgia is a centralised pain syndrome. This hypothesis describes fibromyalgia patients as having augmented pain, and augmented sensory processing in the brain. 
There is increased pain to normally painful stimuli (diffuse hyperalgesia) and pain in response to normally non-painful stimuli (allodynia). Functional magnetic resonance imaging (fMRI) studies show that individuals with FM experience pain and similar brain activation patterns in brain areas involved in pain processing, even when given mild pressure or heat stimuli that most individuals would feel as "touch" rather than "pain". 
Other imaging studies have shown that there is increased connectivity between brain regions involved in increasing pain transmission and decreased connectivity to key antinociceptive regions.
There is also an imbalance between excitatory and inhibitory neurotransmitters. There is an increase in glutamate and nerve growth factor that are facilitate nociception. The gabapentinoids likely work by reducing glutamatergic activity. There is also a decrease in neurotransmitters that inhibit pain or sensory processing like serotoinin, norepinephrine, and GABA. y-hydroxybutyrate and low doses of alcohol may work against low levels of inhibitory GABA. 
The endogenous opioid system is increased, reducing mu-opioid receptor availability. This can work to paradoxically to increase pain. Low-dose naltrexone is thought to target this pathway.
The hypothalamic pituitary adrenal and autonomic nervous systems are frequently abnormal, but studies are inconsistent in the prevalence. Multiple psychosocial factors can influence these aspects of the body. It has even been described as a common final pathway for persistent unresolved activation of an evolutionary conserved stress response.
Around 40-50% of fibromyalgia patients have small fibre neuropathy (SFN). For example, Oaklander et al found that in 41 patients with unexplained widespread pain that started before the age of 21, 59% of children at definite SFN, 17% had probable SFN, and 22% had possible SFN. They then found that in a group of 27 fibromyalgia patients and 30 matched controls, 41% of fibromyalgia patients had definite SFN, compared to 3% in the control group. See Manuel et al for a summary.
Some central sensitisation framework proponents claim that the presence of small fibre neuropathy has unclear relevance, and may be a consequence not a cause of fibromyalgia, with peripheral nervous system changes in response to central nervous system sensitisation. This view is not universally shared. Manuel et al believe fibromyalgia to be related to a persistent hyper-adrenergic state, leading to dorsal root ganglia hyper-excitability, and neuropathic pain. They note the role of dorsal root ganglia sodium channel variants in the condition.
==Clinical Features==
The patient may report persistent pain for over three months, pain in more than one region, intrusive fatigue, impaired memory ("fibro fog"), sleep disturbance, and gastrointestinal disturbance. Other symptoms include increased pain sensitivity (e.g. pain with hugging), muscle stiffness, headaches, anxiety, depression, and irregular periods.
Pain is frequently accompanied by neurologic symptoms e.g. numbness or tingling. It often occurs alongside other chronic pain conditions like migraine, irritable bowel syndrome, endometriosis, and inflammatory arthritis.
A complete rheumatological, orthopaedic, and neurological examination should be performed.
== Diagnosis==
Fibromyalgia has variably been characterised as being under-diagnosed, over-diagnosed, and mis-diagnosed. In one study in the US, the majority of individuals with a clinical diagnosis of fibromyalgia do not fulfil the diagnostic criteria.Walitt B, Katz RS, Bergman MJ, Wolfe F. Three-Quarters of Persons in the US Population Reporting a Clinical Diagnosis of Fibromyalgia Do Not Satisfy Fibromyalgia Criteria: The 2012 National Health Interview Survey. PLoS One. 2016 Jun 9;11(6):e0157235. doi: 10.1371/journal.pone.0157235. PMID: 27281286; PMCID: PMC4900652.
===2010 Criteria===
In 2010 the American College of Rheumatology (ACR) revamped the diagnostic criteria. There is no requirement for a tender point examination like in the ACR 1990 classification. Three criteria must be met for the diagnosis
#Widespread Pain Index (WPI) ≥ 7/19 and Symptom Severity Scale (SSS) Score ≥ 5/12 or WPI between 3–6/19 and SSS ≥ 9/12
#Symptoms being present at a similar level for at least 3 months
#The patient does not have another disorder that would otherwise sufficiently explain the pain.
Conditions 1 and 2 are assessed by the Fibromyalgia Survey Questionnaire.
===2016 Criteria===
The criteria were modified in 2016. A major change was that other conditions don't need to be ruled out and it can be diagnosed irrespective of other diagnoses. WikiMSK has a calculator using this diagnostic criteria. Three criteria must be met
# WPI ≥ 7 and SSS ≥ 5 OR WPI 4 to 6 and SSS ≥ 9
# Generalized pain: at least 4/5 regions
# Have the symptoms in section 3 and pain been present at a similar clinical level for at least 3 months?
==Differential Diagnosis ==
The differential diagnosis must be viewed from two different perspectives. The first perspective is recognising that fibromyalgia type symptoms can occur as a co-morbidity alongside another condition. Fibromyalgia occurs alongside 15-30% of individuals with any autoimmune or chronic musculoskeletal pain condition when there is ongoing nociceptive input. This includes Rheumatoid Arthritis (12-20%), Spondyloarthritis (11-50%), lupus erythematosus (5-25%), Ehlers-Danlos syndrome, sickle cell disease, and cancer pain. 
The second perspective is understanding that some conditions can mimic the symptoms and so the patient has a different diagnosis entirely, and fibromyalgia is not a comorbidity. Examples of this are Polymyalgia Rheumatica, hypothyroidism, and some neuromuscular conditions like statin-induced myopathy.Hochberg. Fibryomyalgia In: Rheumatology. 2019
A problem occurs when considering another disease that has clinical features that can be similar to those with fibromyalgia. An obvious example is metastatic cancer.Differentiating clinically between Small Fibre Neuropathy and Fibromyalgia is challenging. Indicators of SFN are higher pain intensity, length dependent pain pattern (in 80%), stabbing pain and paraesthesia, allodynia; dry eyes/mouth, changed pattern or sweating on body, skin colour alterations/modifications, reduced hair/nail growth on lower extremities, and warm or cold hypoesthesia. Headache and TMJ pain are more common in fibromyalgia. The DN4 questionnaire can be used.
== Investigations ==
First line screening tests to exclude somatic disease are FBC, CRP, CK, calcium, TSH. Other tests to consider are ESR, LFTs, glucose, UEC. 
If there is suspicion of axial spondyloarthritis then consider HLA-B27, and RF if psoriatic. If there is suspicion of Rheumatoid Arthritis then include anti-CCP, and RF. ANA can be considered if there are consistent clinical features.
Vitamin D levels are low in the majority of patients with chronic pain, but this test is not funded in NZ.
fMRI studies are very accurate at identifying fibromyalgia however it is not available in clinical practice. The sensitivity is 92% and specificity 94%.
== Treatment ==
There is no highly effective treatment. In general pharmacological therapies are targeted towards symptoms, and non-pharmacological therapies are targeted towards dysfunction.
=== Education ===
When explaining the condition a useful analogy is an electric guitar. Pain processing is a lot like an electric guitar. To make an electric guitar louder you can either strum the strings harder or turn up the amplifier. The strings in the guitar are equivalent to all the different nerves in different parts of the body. 
All the information (pain, temperature, pressure, etc) comes up through the amplifier which is the spinal cord and the brain. If the amplifier is set high enough - through a combination of genetics and environmental stressors - then pain will occur. Everyone has their own amplifier setting on a range of 0-100. If you happen to have a setting of 70 that is higher than average, but less than fibromyalgia, you will feel more pain. While in fibromyalgia the amplifier is set to 95 or more. Fibromyalgia is not something that either exists or doesn't, but rather there is a degree of "fibromyalgia-ness."
The amplifier in fibromyalgia is not only set higher for pain processing, but for all sensory processing. For example there is increased sensitivity to sounds, lights, smells, and side effects from drugs. Fatigue, insomnia, and memory problems also often occur.
=== Non-pharmacologic Therapies ===
This includes exercise (aerobic +/- strength training), stress management, sleep management, and CBT. If obese then undertaking a calorie restricted diet is effective at improving symptoms of pain and fatigue, particularly if 10% or more weight loss is achieved.
There is modest evidence for manual therapy, massage, yoga, Tai chi, hypnotherapy, biofeedback, balneotherapy, neuromodulation (rTMS and tDCS). Trigger point injections have weak evidence.
=== Medication ===
Best evidence: TCAs, gabapentinoids. Also cyclobenzaprine (at night), duloxetine, and milnacipran but these are not available in NZ. 
Modest evidence: Tramadol, older less selective SSRIs, low dose naltrexone, cannabinoids (CBD alone or low dose THC. Low dose THC may be more effective than high dose). Also gamma hydroxybutyrate but this is not available in NZ.
Not generally effective: Opioid don't tend to work possibly due to reduced mu-opioid receptor availability. In fact, opioids can make fibromyalgia pain worse. NSAIDs, corticosteroids, benzodiazepines are also generally not effective. Ketamine is not effective for fibromyalgia.
=== Surgery Considerations ===
The degree of "fibromyalgia-ness" (even sub-threshold fibromyalgia) is highly predictive of surgical failure and opioid non-responsiveness in patients undergoing arthroplasty and hysterectomy. Each one point increase in fibromyalgia-ness leads to 8mg greater opioid requirement during acute hospitilisation, and 20-25% greater likelihood of surgical failure for knee or hip arthroplasty (success being 50% improvement or much better or very much better on global impression of change). 
==Resources==
==See Also==
*Small Fibre Neuropathy
*Nociplastic Pain
== History of the condition ==
See review by Hauser and colleagues.
==References==
Category:Rheumatology