Type 1 reaction, neuritis and disability in leprosy. What is the current epidemiological situation?

Type 1 reaction is one of the major causes of nerve damage in leprosy patients leading to disabilities of varying severity. Though this complication of leprosy has been extensively described, we still know very little of its natural history and of the factors which may predispose to it. This paper examines the descriptive and analytic epidemiology of these reactions in leprosy. We find that they vary greatly in clinical expression, time of onset, duration and severity, which has important implications for the way they are handled in the context of leprosy-control programmes. We review the various risk factors that have been suggested over the last 30 years and the evidence of their utility in identifying 'high-risk' patients is assessed. We then review the specific aspects of neuritis and disability in leprosy and examine the contribution of Type 1 reaction to leprosy-associated disabilities. The prospects for early detection and prevention of Type 1 reaction are examined in the light of current knowledge, both at research and at the leprosy control level.