## Distinguishing Feature: Skin Lesion Morphology and Sensory Loss ### Tuberculoid vs Lepromatous Leprosy | Feature | Tuberculoid | Lepromatous | |---------|-------------|-------------| | **Lesion borders** | Sharp, well-demarcated | Ill-defined, blurred | | **Sensory loss** | Early and prominent | Late or absent | | **Bacillary load** | Few (paucibacillary) | Numerous (multibacillary) | | **Nerve involvement** | Single nerve, asymmetric | Multiple nerves, symmetric | | **AFB smear** | Negative or scanty | Positive, abundant | | **Lesion distribution** | Localized, few | Widespread, symmetric | ### Key Discriminating Features **Key Point:** The **hypopigmented macule with sharp borders AND early sensory loss** is the hallmark of tuberculoid leprosy and the single best clinical discriminator. This reflects strong cell-mediated immunity that localizes infection and causes nerve destruction early. **Clinical Pearl:** Touch the lesion with a monofilament or pin—if sensation is lost in the lesion but preserved in surrounding skin, tuberculoid leprosy is highly likely. This **loss of sensation within the lesion boundary** is pathognomonic. **High-Yield:** Tuberculoid = **Few lesions, few bacilli, strong immunity, early nerve damage**. Lepromatous = **Many lesions, many bacilli, weak immunity, late or no nerve damage**. **Mnemonic:** **TL = Tiny, Tender (to touch), Tuberoid (raised)** — tuberculoid lesions are few, well-defined, and cause early sensory loss because the immune system walls off the infection. ### Why This Matters The presence of a sharply demarcated lesion with loss of sensation *within* the lesion boundary indicates the host's immune system has successfully contained M. leprae to a localized area, causing local nerve destruction. This is the defining pathological feature of tuberculoid disease and is clinically evident on examination. [cite:Robbins 10e Ch 8]
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