A New VAS-based Diagnostic Tool for Interpreting Pain

The "minimal important difference" for pain improvement is an incredible diagnostic tool that can be used to determine if future endometriosis research projects are successful in mitigating pain.

Key Points

Highlights:

• The authors of this paper seek to identify the "minimal important difference (MID)" for pain improvement as determined by the visual analog scale (VAS). The authors believe that MID will be a useful tool for research projects that hope to see improvement in pain. MID will also be used in the scope of this paper to determine if incremental changes on the VAS scale will also lead to changes in an individual’s quality of life.

Importance:

• This study could impact many subsequent studies that aim to mitigate pain in women with endometriosis.

What’s done here?

• This study is associated with another prospective study that looks at the effects of perturbation on dysmenorrhea and quality of life in women that are given lignocaine. It is important to note that 42 women with endometriosis were included the prospective study, but this study only analyzes the data from 37 of those women. Of these 42 women, some were given the lignocaine treatment and the others were given a placebo, both of which were administered during three consecutive menstrual cycles using an intra-cervical placed balloon catheter.
• All of the participants had a pain score of >50 mm according to the VAS scale.
• All participants were given a pain questionnaire that included a VAS scale before the treatment, after every treatment, and after the 7th, 10th and 13th menstrual cycle.
• The participants were also required to note changes in pain level using the following responses: ‘‘much better,” ‘‘somewhat better,” ‘‘about the same,” ‘‘somewhat worse,” and ‘‘much worse.” This was used to determine MID on the VAS scale. After 4 months independent of treatment, the participants were grouped into categories based on their determination of changes in pain levels.
• An EHP-30 questionnaire, namely its Swedish translation, was used to determine the effects of incrementally changing VAS scores on quality of life.
• Extensive statistical analysis was done on the data in this study.

Key results:

• The results show the MID for improvement on the VAS scale for women with endometriosis is found to be – 39 mm or 49%. This value was higher than expected but is similar to the "minimal clinically important" difference for other diseases that are highly pain, such as arthritis and low back pain.
• The quality of life associated with the aforementioned MID for improvement only changed in certain dimensions. Further testing will be required.

Limitations of the study:

• The study had a small population size and utilized only one anchor to calculate MID.
• The authors state that the VAS scale ratings may be unreliable and imprecise.
• The EHP-30 questionnaire was not given immediately after treatment and this delay could alter the results of the study.

Lay Summary

The visual analog scale (VAS) is a diagnostic tool used by health care providers to evaluate chronic pain in women with endometriosis. In their publication titled “Minimal clinically important difference for pain on the VAS scale and the relation to quality of life in women with endometriosis,” Wickström and Edelstam hypothesize that they can better analyze VAS scale scores using the "minimal important difference (MID)." Not only would it be a useful tool for data interpretation, it would also be an excellent way to determine if incremental changes in VAS scores could lead to changes in an individual’s quality of life. The study in its entirety has been published in Sexual & Reproductive Healthcare. 

The participants in this study were women with endometriosis who had pain scores >50 mm according to VAS scores. This study utilized information from another prospective study where researchers were trying to determine the effects of perturbation using lignocaine, which was administered during three consecutive menstrual cycles. The women in the study were periodically given a pain questionnaire that included a VAS scale. This survey also asked women to analyze the change in their pain, and this was used to determine MID on the VAS scale. All this information above was then used to group the women according to their perceived change in pain. The subsequent effect of the change in pain on quality of life was analyzed using a specific translation of the EHP-30questionnaire. The data derived from this experiment was also subject to statistical analysis.

The results of the study showed that the MID for improvement in women with endometriosis is -39 mm or 49% according to VAS. This information can be utilized in future research to determine a project's success in mitigating pain stemming from endometriosis.

Research Source: https://www.ncbi.nlm.nih.gov/pubmed/28844356