Lepromin skin test

Lepromin Skin Test is a diagnostic tool used in the field of dermatology and infectious diseases to detect the presence of immunity against Mycobacterium leprae, the bacterium that causes leprosy. This test is not used to diagnose active leprosy but rather to determine the type of immune response an individual has to M. leprae, which can help in classifying the form of leprosy and guiding treatment decisions.

Overview

The Lepromin skin test involves the intradermal injection of a standardized extract of heat-killed Mycobacterium leprae organisms. The test is typically performed on the forearm, and the reaction is read 48 to 72 hours later. A positive test, indicated by a nodule or erythema at the injection site, suggests a cell-mediated immune response and is more commonly seen in individuals with the tuberculoid form of leprosy. A negative test, which shows no significant reaction, is often observed in individuals with the lepromatous form of leprosy, indicating a lack of cell-mediated immunity to M. leprae.

Clinical Significance

The Lepromin skin test is primarily of epidemiological and research interest. It helps in understanding the immune response in leprosy and in classifying the disease, which can have implications for treatment and prognosis. The test is not widely used for diagnostic purposes in clinical settings due to its inability to detect active disease directly.

Types of Reactions

There are two types of reactions observed in the Lepromin skin test:

• Fernandez Reaction: A positive reaction occurring within 48 to 72 hours, indicating a strong cell-mediated immune response.
• Mitsuda Reaction: A late reaction observed after 3 to 4 weeks, characterized by the formation of a granuloma at the injection site, also indicative of a cell-mediated immune response.

Limitations

The Lepromin skin test has several limitations. It does not diagnose current leprosy infection but rather indicates past exposure and the type of immune response. The test can also yield false-negative results in individuals with early or very advanced leprosy due to their impaired immune response to M. leprae.

Conclusion

While the Lepromin skin test provides valuable information on the immune response to Mycobacterium leprae, its role in the diagnosis and management of leprosy is limited. It serves more as a research tool in understanding the pathogenesis of leprosy and in classifying the disease for epidemiological studies.