Hansen’s Disease (Leprosy) – The disease and its classification (For professionals)

• The type of disease developed is partially linked to the HLA genes: HLA DR2 and HLA DR3 predispose to tuberculoid disease and HLA–Mt1 to lepromatous disease. Environmental factors such as poor nutrition and poor sanitation play a role through altered immunity in a yet ill-understood mechanism.
• Human disease results from formation of granulomas in the skin and nerve, interspersed with episodes of reactions and eventual permanent damage to peripheral nerves and the long-term consequences of denervation such as neuropathic ulcers and bone-resorption. A wide spectrum of clinical disease can be seen and this is comprehensively included in the Ridley and Jopling classification.

• Classification of leprosy

1. Ridley and Jopling’s classification divide the disease into two polar types: Tuberculoid and Lepromatous. In between, there are Borderline Tuberculoid, Borderline, and Borderline Lepromatous.
2. An alternative classification is the World Health Organisation classification which for purpose of treatment divides leprosy into the Paucibacillary (bacilli absent) group and the Multibacillary (bacilli present) group.

Adapted from Dr Seow Chew Swee: Update on Leprosy