Incidence rates of acute nerve function impairment in leprosy: a prospective cohort analysis after 24 months (The Bangladesh Acute Nerve Damage Study)

In this paper, the incidence rates and cumulative incidence of nerve function impairment (NFI) and leprosy reactions over 24 months follow-up of the prospective cohort of 2664 new leprosy cases are presented. Graphs showing the cumulative incidence of NFI relative to time since registration are presented. Hazard ratios (HRs) for the development of NFI for four variables are given. The majority of patients who developed NFI after registration did so in the first year (67% of multibacillary (MB) patients, and 91% of paucibacillary (PB) patients who developed NFI). Thirty-three percent of all MB patients who developed NFI after registration did so in the second year of follow-up. No PB patients developed NFI for the first time in the last 6 months of follow-up. However, seven NFI events occurred amongst PB patients in that period, amongst those who had already had one NFI event. The incidence rate (IR) of NFI amongst MB patients was 24/100 person-years at risk (PYAR), and amongst PB patients was 1.3/100 PYAR. The HR for the development of NFI amongst MB patients compared with PB patients was 16 using univariate analysis. Amongst patients who had long-standing NFI present at registration, the IR was 27/100 PYAR compared with 1.7/100 PYAR amongst those who did not have long-standing NFI. The HR for developing acute NFI amongst those with longstanding NFI present at registration compared with those without was 14 using univariate analysis. When multivariate regression analysis is applied, the apparently significant univariate HRs for sex and age disappeared. The resultant multivariate HR for leprosy group is 8.8, and 6.1 for the presence/absence of long-standing NFI at registration. In all, 142/166 (86%) of all new NFI events were silent, underlining the need for regular nerve function testing. IRs are presented for the four 6-month periods of the 24-month follow-up. They show a clear stepwise reduction over the total period. The IRs amongst MB patients and those with long-standing NFI present at registration are very high at 34 and 41/100 PYAR, respectively, for the first 6 months of follow-up. Even during the final 6-month period, the IR is maintained at a moderately high level (18 and 15/100 PYAR, respectively).