Revalidation of various clinical criteria for the classification of leprosy--a clinic-pathological study

WHO guidelines classify leprosy patients clinically into PB and MB group based on the number of skin lesions (NSL) with > or = 6 skin lesions as a criterion for MB leprosy. Other clinical criteria for classification are based on the number of body areas affected (NBAA) and on size of the largest skin lesions (SLSL). They are also fairly simple and easily practicable in the field.

The objective of this study is to explore whether sensitivity and specificity of the WHO classification can be improved by addition of clinical criteria based on NBAA and SLSL to WHO classification.

Among 100 newly diagnosed untreated leprosy patients classified into PB and MB group according to WHO classification, the NSL and NBAA were recorded and the size (longest diameter) of largest skin lesion was measured in centimeters. The Receiver Operator Characteristic (ROC) curves were plotted for each parameter to find the best cut off point (with highest sensitivity and specificity).

The sensitivity and specificity of the WHO classification tested, using slit-skin smear (SSS) and skin biopsy results as the gold standard, was found to be 63% and 85% respectively. The ROC curve for NSL found the best cut off of three and more lesions for MB group (sensitivity 90% & specificity 80%). Similarly, ROC curves for NBAA and SLSL found the best cut off points for classification into MB group to be two or more (sensitivity 90% & specificity 75%) and 5 cm or more (sensitivity 87% and specificity 65%) respectively. On combining all these criteria together sensitivity was increased to 98.5% with no significant change in specificity, which was 77.5%.

The study concluded that the sensitivity of the present clinical classification can be further improved by addition of two other clinical criteria.