## Distinguishing Features of Lepromatous vs Tuberculoid Leprosy ### Bacillary Load and Morphology **Key Point:** Lepromatous leprosy (LL) is characterized by an extremely high bacillary load (>10^6 organisms per gram of tissue), while tuberculoid leprosy (TT) has a low bacillary load (<10^2 organisms per gram of tissue). ### Clinical and Microbiological Comparison | Feature | Lepromatous Leprosy (LL) | Tuberculoid Leprosy (TT) | |---------|--------------------------|-------------------------| | **Bacillary load** | Very high (>10^6/g tissue) | Very low (<10^2/g tissue) | | **Acid-fast bacilli in smear** | Numerous, easily detected | Few or absent | | **Lesion definition** | Poorly defined, ill-demarcated | Sharply demarcated, well-defined | | **Lesion appearance** | Macules, papules, nodules, diffuse infiltration | Hypopigmented macules, plaques | | **Lepromin test (Mitsuda)** | Negative (no cell-mediated immunity) | Positive (strong CMI) | | **Nerve involvement** | Late and symmetric | Early and asymmetric | | **Immune response** | Th2-dominant (humoral) | Th1-dominant (cell-mediated) | **High-Yield:** The bacillary load and lepromin test status are the most reliable discriminators between LL and TT. LL patients are highly infectious due to massive bacillary shedding; TT patients are minimally infectious. ### Clinical Pearl **Clinical Pearl:** In LL, lesions are numerous and poorly demarcated because the host's cell-mediated immunity is severely impaired, allowing unrestricted mycobacterial proliferation. In TT, the strong CMI response localizes the infection, creating sharply defined lesions with few organisms. ### Mnemonic **Mnemonic:** **"LL = Load, TT = Test"** - **LL** = **L**epromatous has **L**arge load - **TT** = **T**uberculoid has **T**est positive (lepromin) [cite:KD Tripathi 8e Ch 47]
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.