Primary and secondary fibromyalgia share the same symptom burden, according to the polysymptomatic distress (PSD) scale, a tool that measures fibromyalgia symptom severity, a study reports.
The study, “Primary and Secondary Fibromyalgia Are The Same: The Universality of Polysymptomatic Distress,” was published in The Journal of Rheumatology.
Fibromyalgia is characterized by widespread muscle pain, fatigue, sleep disturbance, and memory and mood issues. Chronic pain, one of the hallmarks of the condition, is caused by alterations in the brain and the central nervous system, which causes the body to overreact to pain and other external stimuli, such as noise, smell, and bright lights.
Fibromyalgia can be considered either primary, or dominant, also known as idiopathic fibromyalgia, or secondary. In the primary form, the causes of the disorder are unknown, but in secondary fibromyalgia, the disorder usually occurs alongside other debilitating medical conditions, such as rheumatoid arthritis (RA), lupus, and multiple sclerosis.
The PSD scale is a tool developed to measure symptom severity and aid in fibromyalgia diagnosis. It assigns five different severity categories (none, mild, moderate, severe, and very severe) to measure symptoms.
Previous studies already demonstrated that the PSD scale is able to predict, with more than 90% accuracy, whether a patient who meets the fibromyalgia criteria actually has the disorder.
In this study, researchers wanted to test whether symptom severity measured by the PSD scale would be similar between primary and secondary fibromyalgia, as well as to what extent these symptoms are comparable to other individuals who do not meet the fibromyalgia criteria. When patients did not meet the fibromyalgia criteria established by authors in a previous study, they were considered “potential” cases.
A total of 1,525 patients with a clinical diagnosis of fibromyalgia (considered the potential or actual group of primary fibromyalgia) and 12,037 with RA (considered the potential or actual group of secondary fibromyalgia) were analyzed in the study.
Investigators used regression models to compare patients with potential or actual primary fibromyalgia to RA patients with potential or actual secondary fibromyalgia for 17 different clinical variables.
When controlled for PSD, the widespread pain index (a measure of how spread is the pain experienced by the patient), symptom severity scale, pain, global quality of life, and other physical and mental component scores were equivalent between primary and secondary fibromyalgia. The health assessment questionnaire-disability index (a measure of how RA patients’ disabilities affect their daily life) and the painful joint count scores were both slightly higher in secondary fibromyalgia, with 0.21 units and 1.6 joints, respectively.
PSD scores between patients who did not meet the fibromyalgia criteria and those who did were also similar.
These findings suggest that there are no significant differences in symptom burden between primary and secondary fibromyalgia. Researchers also believe their findings reinforce the use of PSD scores, since they are more informative regarding disease severity than other diagnostic tools limited to either a “healthy” or “disease” state.
Investigators also highlighted the importance of using disease controls with PSD scores matching those from the experimental groups, instead of comparing healthy individuals with diseased subjects.
“If controls are just healthy individuals, a distorted and misleading picture emerges because, in effect, we are examining subjects at the 2 ends of the PSD distribution curve: many symptoms versus no symptoms,” the authors wrote. “Our current study, by showing the equivalency of PSD and criteria in RA and PFM, suggests that FM could be studied in diseases where there is no selection bias in patient participation, such as RA.”