Objective: To provide a better empirical understanding of the dimensionality of neuropathic and non-neuropathic pain quality.
Method: An exploratory factor analysis (FA) was performed with baseline pain quality data [assessed using the Pain Quality Assessment Scale (PQAS)] from patients with osteoarthritis of the knee (n=368) and low back pain (n=455) who had participated in a series of analgesic clinical trials. The results of the FA were then confirmed in a sample of patients with neuropathic pain secondary to carpal tunnel syndrome (n=138). Comparisons between the diagnostic groups on scale scores derived from the FA results were also made using t tests.
Results: Three clear pain quality factors emerged that seemed to represent (1) paroxysmal pain sensations (PQAS descriptors: shooting, sharp, electric, hot, and radiating), (2) superficial pain (itchy, cold, numb, sensitive, and tingling), and (3) deep pain (aching, heavy, dull, cramping, and throbbing). The PQAS tender pain item did not load strongly on any of the 3 factors.
Discussion: The findings support the hypothesis that pain qualities cluster into distinct groups. If replicated in additional samples, the pain quality domains identified may provide clinicians and researchers with a useful way to summarize data from pain quality measures, and may also provide meaningful end points that would allow for treatment differentiation between various pharmacologic entities.
*Endo Pharmaceuticals Inc, Chadds Ford, PA
†Department of Rehabilitation Medicine, University of Washington School of Medicine, Seattle, WA
‡Merck and Co Inc, Whitehouse Station, NJ
§Nuvo Research Inc, Mississauga, Ontario, Canada
Portions of the findings presented in this paper were presented at the 9th International Conference on the Mechanisms and Treatment of Neuropathic Pain, November 2-4, 2006, Bermuda.
Reprints: Timothy W. Victor, PhD, Endo Pharmaceuticals Inc, 100 Endo Boulevard, Chadds Ford, PA 19317 (e-mail: firstname.lastname@example.org).
Received for publication October 18, 2007; revised January 17, 2008; accepted January 25, 2008