Fibromyalgia is a chronic medical condition that is characterised by widespread pain, fatigue, waking unrefreshed and cognitive disorders. In the field of musculoskeletal medicine in New Zealand, the highly subjective nature of the diagnostic criteria has meant that it is a controversial diagnosis in this specialty. Recent work has found that 40-50% of patients have small fibre neuropathy.
Fibromyalgia is present across the world, and has a prevalence ranging between 2% to 4%.
A popular 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 connectivity to pro-nociceptive brain regions, and decreased connectivity to anti-nociceptive regions. Psychological and other stressors are often a factor in the development and maintenance of the disorder, with the presence of sympathetic dysfunction.
Fibromyalgia has also been described as a sympathetically maintained or dysautonomia-related neuropathic pain syndrome. The pain has neuropathic features, and is independent of stimulus, and may be accompanied by allodynia and paraesthesias. Nociceptive fibres may be sensitised.
The current criteria for fibromyalgia were established in 2010 by the American College of Rheumatology (ACR). 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.
Small Fibre Neuropathy
- Main article: Small Fibre Neuropathy
There has been a large amount of research confirming the presence of small fibre neuropathy (SFN) in some fibromyalgia patients. Overall it appears that around 40-50% of fibromyalgia patients actually have SFN - a neuropathic pain syndrome.
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.
- Maslinska et al. Small fibre neuropathy as a part of fibromyalgia or a separate diagnosis? Int. J. Clin. Rheumatol. (2018) 13(6), 353-359. Full Text
- Martínez-Lavín Fibromyalgia and small fiber neuropathy: the plot thickens!. Clinical rheumatology 2018. 37:3167-3171. PMID: 30238382. DOI.
- Oaklander & Klein Evidence of small-fiber polyneuropathy in unexplained, juvenile-onset, widespread pain syndromes. Pediatrics 2013. 131:e1091-100. PMID: 23478869. DOI. Full Text.
- Oaklander et al. Objective evidence that small-fiber polyneuropathy underlies some illnesses currently labeled as fibromyalgia. Pain 2013. 154:2310-6. PMID: 23748113. DOI. Full Text.