Development and validation of a severity scale for leprosy type 1 reactions

Abstract

Objectives: To develop a valid and reliable quantitative measure of leprosy Type 1 reactions.

Methods: A scale was developed from previous scales which had not been validated. The face and content validity were assessed following consultation with recognised experts in the field. The construct validity was determined by applying the scale to patients in Bangladesh and Brazil who had been diagnosed with leprosy Type 1 reaction. An expert categorized each patient's reaction as mild or moderate or severe. Another worker applied the scale. This was done independently. In a subsequent stage of the study the agreement between two observers was assessed.

Results: The scale had good internal consistency demonstrated by a Cronbach's alpha >0.8. Removal of three items from the original scale resulted in better discrimination between disease severity categories. Cut off points for Type 1 reaction severities were determined using Receiver Operating Characteristic curves. A mild Type 1 reaction is characterized using the final scale by a score of 4 or less. A moderate reaction is a score of between 4.5 and 8.5. A severe reaction is a score of 9 or more.

Conclusions: We have developed a valid and reliable tool for quantifying leprosy Type 1 reaction severity and believe this will be a useful tool in research of this condition, in observational and intervention studies, and in the comparison of clinical and laboratory parameters.

Figure 1. Test sites on the hands (2 and 10g) and the feet (10 and 300g).

Figure 2. Box plot of the Original Scale Scores by expert severity classification showing medians, interquartile ranges and minimum and maximum scores.

Figure 3. A Bland Altman plot of the difference between the scores of the examiners and the mean of those scores (n = 39).

Figure 4. ROC curve for mild and moderate cases and moderate and severe cases.