A clinical prediction rule for nerve-function impairment in leprosy patients

Background: Nerve-function impairment (NFI) commonly occurs during or after chemotherapy in leprosy and is the hey pathological process leading to dis ability and handicap. We describe the development of a simple clinical pred iction rule for estimating the risk of NFI occurrence. Methods: New leprosy cases who presented to a centre in Bangladesh were rec ruited and followed up for 2 years in a field setting. We used multivariabl e regression analysis by Cox's proportional hazards model to identify predi ctive variables for NFI. Discriminative ability was measured by a concordan ce statistic. Internal validity was assessed with bootstrap resampling tech niques. Findings: 2510 patients were followed up for 2 years, 166 developed NF. A s imple model was developed with leprosy group (either paucibacillary leprosy [PB] or multibacillary leprosy [MB]) and the presence of any nerve-functio n loss at registration as predictive variables. Patients with PB leprosy an d no nerve-function loss had a 1.3% (95% CI 0.8-1.8%) risk of developing NF I within 2 years of registration; patients with PB leprosy and nerve-functi on loss, or patients with MB leprosy and no nerve-function loss had a 16.0% (12-20%) risk; and patients with MB leprosy with nerve-function loss had a 65% (56-73%) risk. Interpretation: Our prediction rule can be used to plan surveillance of new leprosy patients. Patients at low risk of NFI may need no follow-up beyond their course of chemotherapy (6 months); patients with intermediate risk n eed a minimum of 1 year of surveillance; and patients with high risk should have at least 2 years of surveillance for new NFI. Current recommendations for surveillance of patients with leprosy (for the duration of chemotherap y only) exclude an important group of patients who are at risk of developin g NFI after completion of treatment.