Background: Nerve function impairment (NFI) is the key outcome of the pathological processes of infection with Mycobacterium leprae, which can continue after completion of multidrug therapy (MDT) and lead to disability after leprosy patients are released from treatment. The objective of this study was to assess the need for and duration of surveillance of NFI.
Methods: Prospective cohort study of 2664 new leprosy patients in Bangladesh, with an observation period of 36 months in paucibacillary (PB) patients, and 60 months in multibacillary (MB) patients. Incidence rates (IR) were calculated with the number of patients developing NFI, type 1 and type 2 reactions, and silent neuritis for the first time after registration as the numerator, and cumulative person-years at risk (PYAR) as the denominator. Survival curves to the first event of NFI were also calculated.
Results: The IR of first event of NFI amongst MB patients was 16.1 per 100 PYAR, with 121/357 (34%) developing NFI during the observation period. Of the 121 with a first event of NFI, 77 (64%) had this within a year after registration, 35 (29%) in the second year, and the remaining 9 (7%) after 2 years. The IR of first event of NFI amongst PB patients was 0.9 per 100 PYAR, with 54/2153 (2.5%) developing NFI during the observation period. Of the 54 with a first event of NFI, 48 (89%) had this within a year after registration, 3 (5.5%) in the second year, and the remaining 3 (5.5%) cases after 2 years. The percentage of PB patients with no NFI at registration surviving without developing NFI during the observation period was 99% and for PB patients with NFI at registration 92%. In MB patients without NFI at registration, the percentage surviving with no NFI during the observation period was 84% and for MB patients with NFI at registration only 36%.
Conclusion: New episodes of NFI and reactions after registration are common, in particular in MB patients with long-standing NFI at registration. The study highlights the importance of continuing surveillance for NFI of this risk group after registration for 2 years. Active surveillance beyond 2 years is not indicated.