There have been discrepancies to difficulties to assess a subjective experience such as mood or pain. The difficulties will remain constant from one measurement interval to the next, and especially from one person to another. As for within-subject comparisons, VAS was suited to experimental designs, and Ohnhaus and Adler (1975) and Joyce et al. (1975) found the VAS-pain were more sensitive than the other verbal rating scales (ex. 5-point scales). However, its suitability for between-subject comparisons has been questioned for the reasons that the equivalent positioning of marks on lines by different people does not necessarily convey that they experienced the same pain. Although VAS provide easily the numerical values for statistical analysis, there have been some problems underlying the use of VAS as a sophisticated statistical technique. There have been two ways to treat the length of the line as the evaluation of pain intensity in statistical analysis. The one equates the length of the line produced by the subject's mark with the estimation of pain as though the subjects were able to effect one-to-one correspondence between VAS and the pain intensity (parametric or cardinal). The other prefers to treat as the data so obtained non-parametrically (ordinal). It should be noted that subjects did not necessarily attach the same meanings to the same absolute scores. Subjective estimates like the VAS do not qualify as interval level scores and are thus not suited for the operations of addition and subtraction and calculations of averages. (Chapman 1976) The use of rank based non-parametric statistical procedures helps to overcome some of the difficulties associated betwwn-subject comparisons with the VAS, as procedures are based on the assumptions that the data cannot be classified into particular distributions and that its scaling can be represented by ranks. VAS pain scores obtained in our patients with Herpes Zoster or RSD were treated as ordinal scales and statistical analyses were carried out by use of non-parametric method (Wilcoxon signed rank test, Kruskal Wallis test or Friedman 2 way-ANOVA). These results have been presented.
The focus of this brief review is treatments that are effective for patients with neuropathic pain. We will discuss these treatments in the context of neural mechanisms that are thought to contribute to pain following peripheral nervous system injury or dysfunction. Although some mechanisms come into play only when the nervous system is damaged others are operative under physiological conditions and contribute to pain even when there is no neural damage or dysfunction. Regardless of whether pathological or physiological, each mechanism offers a potential point for treatment. In this chapter, we will relate therapeutic interventions to particular pain mechanisms, and review the available clinical evidence for the efficacy of such treatments. Finally, current therapeutic options will be discussed in the context of a treatment trials algorithm for peripheral neuropathic pain.
In certain instances it can be demonstrated that pain is dependent on sympathetic innervation of the painful area. Sympathetically maintained pain (SMP) is the term that has been coined to describe this circumstance. Sympathetically independent pain (SIP) is the phrase used to refer to those patients whose pain is independent of sympathetic innervation of the painful area.