The lepromin test (Mitsuda test) is positive in which form of leprosy?

Explanation

## Lepromin Test (Mitsuda Test) in Leprosy Classification **Key Point:** The lepromin test is positive in tuberculoid and borderline tuberculoid forms of leprosy, reflecting a strong cell-mediated immune response (Th1). It is negative in lepromatous leprosy due to immune suppression. ### Immunological Basis **Mnemonic:** **CELL-mediated = TuBerculoid positive; Humoral = Lepromatous negative** The lepromin test measures delayed-type hypersensitivity (DTH) to M. leprae antigens: - **Positive test** = Strong Th1 response (IL-2, IFN-γ) - **Negative test** = Th2 response dominance (IL-4, IL-10) ### Classification and Lepromin Status | Leprosy Form | Lepromin Test | Bacillary Load | Cell-Mediated Immunity | Lesion Characteristics | | --- | --- | --- | --- | --- | | Tuberculoid (TT) | **Positive** | Few (1–5) | Strong | Well-defined, few lesions | | Borderline Tuberculoid (BT) | **Positive** | Few to moderate | Strong | Asymmetric lesions | | Mid-Borderline (BB) | Weakly positive/negative | Moderate | Intermediate | Unstable form | | Borderline Lepromatous (BL) | **Negative** | Moderate to many | Weak | Numerous lesions | | Lepromatous (LL) | **Negative** | Numerous (100+) | Absent/suppressed | Ill-defined, symmetric | | Indeterminate | Negative or weakly positive | Variable | Developing | Early, non-specific | **High-Yield:** Lepromin positivity correlates with: - Better prognosis - Fewer bacilli - Fewer complications - Shorter treatment duration ### Clinical Pearl **Warning:** The lepromin test should NOT be used for diagnosis of active leprosy because: - It becomes positive only after 3–6 weeks - It reflects immune status, not active infection - Slit-skin smear and histopathology are diagnostic tools The lepromin test is used for: - **Classification** of leprosy type - **Prognosis** assessment - **Monitoring** immune reconstitution during treatment ### Interpretation Timeline - **Read at 3 weeks** (Mitsuda reaction) — most clinically relevant - **Read at 24–48 hours** (Fernandez reaction) — non-specific, less useful [cite:Park 26e Ch 31]