Part 1: Ridley-Joplin Classification of leprosy

Depending upon the immunological resistance of persons to Mycobacterium leprae, leprosy can present with different clinical signs. The resistance of individuals varies from very strong to nil, with all possible grades in between.

Thus leprosy can be characterised by high resistance & low number of bacilli (tuberculoid leprosy) or it can be characterised by very low resistance and high number of bacilli (lepromatous leprosy). Between these two ends of the spectrum, there is decrease in resistance and increase in number of bacilli in the body giving rise to borderline tuberculoid, borderline and borderline lepromatous kinds of leprosy. This classification was proposed by Ridley and Joplin.

In addition, an early stage of disease, indeterminate leprosy' is recognised that can be self-healing or may develop any of the above-mentioned forms.