Research Article: Preventing Nerve Function Impairment in Leprosy: Validation and Updating of a Prediction Rule

Date Published: August 27, 2008

Publisher: Public Library of Science

Author(s): Ron P. Schuring, Jan H. Richardus, Ewout W. Steyerberg, David Pahan, William R. Faber, Linda Oskam, Diana N. J. Lockwood

Abstract: BackgroundTo validate and update a prediction rule for estimating the risk of leprosy-related nerve function impairment (NFI).Methodology/Principal FindingsProspective cohort using routinely collected data, in which we determined the discriminative ability of a previously published rule and an updated rule with a concordance statistic (c). Additional risk factors were analyzed with a Cox proportional hazards regression model. The population consisted of 1,037 leprosy patients newly diagnosed between 2002 and 2003 in the health care facilities of the Rural Health Program in Nilphamari and Rangpur districts in northwest Bangladesh. The primary outcome was the time until the start of treatment. An NFI event was defined as the decision to treat NFI with corticosteroids after diagnosis. NFI occurred in 115 patients (13%; 95% confidence interval 11%–16%). The original prediction rule had adequate discriminative ability (c = 0.79), but could be improved by substituting one predicting variable: ‘long-standing nerve function impairment at diagnosis’ by ‘anti-PGL-I antibodies’. The adjusted prediction rule was slightly better (c = 0.81) and identified more patients with NFI (80%) than the original prediction rule (72%).Conclusions/SignificanceNFI can well be predicted by using the risk variables ‘leprosy classification’ and ‘anti-PGL-I antibodies’. The use of these two variables that do not include NFI offer the possibility of predicting NFI, even before it occurs for the first time. Surveillance beyond the treatment period can be targeted to those most likely to benefit from preventing permanent disabilities.

Partial Text: Preventing permanent disabilities due to nerve function impairment (NFI) [1] remains a major concern in leprosy control. Mycobacterium leprae, the causative agent of leprosy, infiltrates Schwann cells of peripheral nerve fibers [2]. Subsequently, the nerve fibers can be damaged by accumulation of bacteria and hypersensitivity reactions of the immune system. The decline of nerve function can take place before, during and/or after leprosy treatment. Early detection (within 6 months) and corticosteroid treatment may prevent further decline [3]. With leprosy control becoming less specialized and increasingly integrated into general health care services, there is a need for simplified procedures at the field level for timely identification and treatment of NFI in leprosy patients. The chances of preventing disability increase when health care workers pay special attention to patients who have a high risk of developing NFI.

NFI occurred in 115 of 864 patients (13%; 95% confidence interval [CI] 11–16%).

Predicting NFI is important for identifying new leprosy patients that are at risk for nerve damage and, consequently, permanent disability. We describe an adjusted NFI prediction rule that replaces the variable ‘longstanding NFI at diagnosis’ with ‘anti-PGL-I antibodies’. The adjusted prediction rule was better able to identify patients at risk of developing NFI after diagnosis.



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