31st January 2024

Background

Epidemiology 

Fibromyalgia and chronic regional pain syndrome are both chronic pain syndromes. Fibromyalgia affects approximately 2% of people, typically occurring between the ages of 30 – 50 years, with women being more commonly affected than men. Fibromyalgia constitutes up to 10% of new referrals to the Rheumatology department. The condition is associated with several risk factors, including female sex, low household income, middle-aged, divorced, and low educational status. 

Chronic Regional Pain Syndrome (CRPS) is a less common syndrome. There are reports of incidence rates in Europe of 26 per 100,000 patient-years. Many cases may go undiagnosed or misdiagnosed, making estimates of prevalence difficult. This condition is more common in females and appears to be highest in postmenopausal women.

Pathophysiology 

Fibromyalgia causes disordered pain regulation. The pathophysiology of this condition is not fully understood, and there are many suggested theories. No causative gene has been found; however, studies have shown that first-degree relatives of fibromyalgia patients are more likely to develop the condition themselves. Evidence suggests that it is related to central rather than peripheral neurological mechanisms. Underlying central sensitisation is likely present, with exaggerated central nervous system neural signalling, resulting in greater than normal increases in perceived pain termed temporal summation of pain. There is also dysregulation of the spinal cord responses to painful stimuli via the descending inhibitory pain pathway. Alongside this, there is a reduced ability to inhibit non-painful sensory stimuli following repetitive stimulation. This occurs in the absence of muscle disease or inflammation. Biochemical factors also play a role in upregulation of pain receptors and neurotransmitters, including substance P, which has been found to be increased in the cerebrospinal fluid (CSF) of fibromyalgia patients. 

The pathogenesis of CRPS is poorly understood. There are proposed theories, including classic inflammation, neurogenic inflammation, peripheral and central sensitisation, altered sympathetic nervous system function and dysregulated pain perception within the central nervous system. Some studies have also demonstrated an increase in proinflammatory cytokines in affected tissue and CSF.

References

• Macfarlane, G. J., Kronisch, C., Dean, L. E. et al. EULAR revised recommendations for the management of fibromyalgia. Annals of the Rheumatic Diseases, 2017;76(2), 318. 
• National Health Service. Fibromyalgia. [Internet]. nhs.uk. 2019. [cited 29 April 2022]. Available from: https://www.nhs.uk/conditions/fibromyalgia/
• Wilkinson, I. B., Raine, T., Wiles, K., Goodhart, A., Hall, C., & O’Neill, H. (2017). Oxford Handbook of Clinical Medicine (Tenth Edition). Oxford University Press. P. 558 
• Dedhia, J. D., & Bone, M. E. (2009). Pain and fibromyalgia. Continuing Education in Anaesthesia Critical Care & Pain, 9(5), 162–166. https://doi.org/10.1093/bjaceaccp/mkp026
• UpToDate [Internet]. Pathogenesis of Fibromyalgia. Uptodate.com. 2021 [cited 29 April 2022]. Available from: https://www.uptodate.com/contents/pathogenesis-of-fibromyalgia?search=pathogenesis%20of%20fibromyalgia&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1
•  Royal College of Physicians. Complex Regional Pain Syndrome in Adults, UK guidelines for diagnosis, referral and management in primary and secondary care. 
• Goebel A, Barker CH, Turner-Stokes L et al. Complex regional pain syndrome in adults: UK guidelines for diagnosis, referral and management in primary and secondary care. Royal College of Physicians. 2012.
• National Health Service. Complex Regional Pain Syndrome. [Internet]. nhs.uk. 2019. [cited 29 April 2022]. https://www.nhs.uk/conditions/complex-regional-pain-syndrome/
• UpToDate [Internet]. Complex Regional Pain Syndrome in Adults: Pathogenesis, Clinical Manifestations and Diagnosis. Uptodate.com. 2021 [cited 29 April 2022]. Available from: https://www.uptodate.com/contents/complex-regional-pain-syndrome-in-adults-pathogenesis-clinical-manifestations-and-diagnosis?search=chronic%20regional%20pain%20syndrome&source=search_result&selectedTitle=1~150&usage_type=default&display_rank=1