Two composite constructs of symptom patterns in Chronic Overlapping Pain Conditions (COPCs) — Generalized Sensory Sensitivity (GSS) and Sleep, Pain, Affect, Cognition, Energy (SPACE), representing elevated somatic and external sensitivity, and increased constitutional symptom severity, respectively — were found to be associated with each other and the centralized pain phenotype across COPC cohorts, according to a study published in Pain.
Disordered pain processing in the central nervous system often results in a diverse mix of symptoms broadly referred to as “centralized pain,” which is experienced by patients with COPC. These symptom clusters are widely prevalent and notoriously difficult to treat in conditions such as fibromyalgia, temporomandibular disorder, and chronic pelvic pain. Investigators sought commonalities across several conditions that would enable more precise characterization and description of these clusters and allow distinction from peripheral pain sources.
Using data from the Multidisciplinary Approach to the Study of Chronic Pelvic Pain Research Network (Clinicaltrials.gov identifier: NCT01098279), 3 cohorts consisting of patients with Urologic Chronic Pelvic Pain Syndrome (UCPPS) (n=424; mean age, 43; 55% women), patients with other mixed-pain COPCs (n=200; mean age, 42; 78% women) and healthy control participants (n=415; mean age, 41; 56% women) were examined. The mixed pain cohort included individuals diagnosed with fibromyalgia or temporomandibular disorder , as well as irritable bowel syndrome, chronic fatigue syndrome, and migraine. The UCPPS subgroup was assessed at baseline and 6 and 12 months, and participants in the other 2 groups were only evaluated at baseline.
The study participants were evaluated for pain severity, urinary symptom severity, sleep and fatigue, cognitive dysfunction, depression, spatial pain extent, and disability. The Complex Medical Symptom Inventory offered insight into patients’ total symptom burden and the presence of COPCs.
The 2-factor model of GSS and SPACE fit adequately across all 3 cohorts, and the factors were associated with each other (UCPPS φ = 0.638; 95% CI, 0.554-0.721; mixed pain φ = 0.808; 95% CI, 0.727-0.888; healthy control participants φ = 0.503; 95% CI, 0.395-0.611). In addition, this structural model showed stability over time up to one year in the UCPPS group, indicating reproducibility.
Increased SPACE scores correlated significantly with disability measures (β = −0.175; 95% CI, −0.300 to −0.050; P =.006) and more severe urinary symptoms (β = 0.181; 95% CI, 0.223-0.491; P <.001). The GSS construct was most strongly associated with the presence of comorbid COPCs. “These factors may represent important and distinct continuum of symptoms that are indicative of the centralized pain phenotype at high levels,” noted the investigators.
Study limitations included the absence of long-term clinical outcomes, potential for improvement in construct definitions, and the possibility that the UCPSS may comprise separate distinct conditions.
“Exploratory and confirmatory factor analyses support a two-factor model of centralized pain, with strong associations between the two factors. This basic two-factor structure was apparent in each cohort,” concluded the authors. They recommended that future longitudinal trials explore COPC symptom trajectories and therapeutic responses.
Schrepf A, Williams DA, Gallop R, et al. Sensory sensitivity and symptom severity represent unique dimensions of chronic pain. Pain. May 2018:1-28. doi:10.1097/j.pain.0000000000001299