Validity of the WHO operational classification and value of other clinical signs in the classification of leprosy.

The objective of this study is to examine the validity of the WHO operational classification using skin smear results as the gold standard and explore the value of additional clinical signs independently and in combination with the WHO classification. Between 1985 and 2000, 5439 new untreated leprosy patients were registered at the Schieffelin Leprosy Research and Training Center, Karigiri. They were classified according to the Ridley Jopling classification as well as WHO operational classification based on the number of skin lesions. The sensitivity and specificity of the WHO operational classification tested, using skin smear results as the gold standard, was found to be 88.6% and 86.7% respectively. The Receiver Operator Characteristic (ROC) curve confirms that the best option for sensitivity and specificity is a cut off of 6 and more lesions for MB. The validity of the number of enlarged nerves and size of the largest skin lesion as independent criteria to classify patients was found to be poor. Addition of three enlarged trunk nerves to the WHO classification improved its sensitivity to 91.4%, while the specificity remained almost unchanged at 85.3%. Addition of the size of the largest skin lesion to the WHO classification reduced its validity considerably. The study concludes that the WHO recommendation of using six and more lesions for classifying a patient as MB is the best option available at the moment, and calls for further research to identify other clinical criteria that have a better validity and could be easily applied in the field.