Hansen’s Disease (Leprosy) – Diagnostic tests (For professionals)

• Histological examination of the skin lesion and nerve for the typical histological changes and the presence of acid-fast bacilli is required for the definitive diagnosis of leprosy. All cases of leprosy should preferably be confirmed histologically as labeling a person with leprosy carries with it dire social and medical implications.
• Slit skin smear to detect acid-fast bacilli from lesional skin provides a fast confirmation of multibacillary leprosy. It is also useful for monitoring progress of patients with multibacillary leprosy undergoing treatment. The test requires trained personnel to be reliable. It is cheap but unfortunately, not easily available. While a positive test confirms diagnosis of leprosy, a negative test does not exclude it. The indices reported are Bacterial Index (BI), which measures the total number of bacilli, and Morphological Index (MI), which measure the percentage of viable bacilli in the specimen.
• Lepromin test is an intradermal test with autoclaved Mycobacterium leprae antigen. It is a guide to the cell- mediated immunity (Mitsuda and Fernandes reactions) of the patient against leprosy. It is not useful in confirming a diagnosis of leprosy, but a negative test can be useful to exclude leprosy in patients with peripheral neuropathy.
• Phenolic glycolipid-1 (PGL-1) IgM antibody detection is of limited clinical use. It is positive in 100% of Multibacillary leprosy but in only 21 % in Paucibacillary leprosy and 14% in household contacts. There is a great need for a practical, sensitive and specific serological test for diagnosis of pre-clinical leprosy but this is presently not available.

Adapted from Dr Seow Chew Swee: Update on Leprosy