A 32-year-old woman from rural Maharashtra presents with a painless, indurated ulcer on her left shin for 8 months. The ulcer has a punched-out appearance with undermined edges and a granulating base. She reports a history of pulmonary tuberculosis treated 2 years ago. Examination reveals regional lymphadenopathy. A biopsy shows caseating granulomas with acid-fast bacilli on Ziehl-Neelsen staining. Which type of cutaneous tuberculosis is most likely?

Explanation

## Diagnosis: Scrofuloderma **Key Point:** Scrofuloderma is cutaneous tuberculosis resulting from direct extension of tuberculosis from underlying lymph nodes, bones, or joints to the overlying skin. ### Clinical Features of Scrofuloderma - **Presentation:** Painless, indurated ulcer with punched-out appearance and undermined edges - **Location:** Commonly over lymph nodes (neck, axilla, groin) or joints - **Progression:** Starts as nodule → abscess → ulceration with granulating base - **Lymphadenopathy:** Regional lymph nodes are typically involved and may show sinuses - **Histology:** Caseating granulomas with acid-fast bacilli (diagnostic) ### Differential Features of Other Forms | Form | Source | Clinical Features | Histology | |------|--------|-------------------|----------| | **Scrofuloderma** | Direct extension from lymph nodes/bones | Ulcer over nodes, undermined edges | Caseating granulomas, AFB+ | | **TB verrucosa cutis** | Inoculation TB | Verrucous plaque, minimal ulceration | Minimal caseation | | **TB luposa** | Hematogenous spread | Soft nodules, "apple jelly" appearance | Minimal caseation | | **Lichen scrofulosorum** | Hematogenous (hypersensitivity) | Lichenoid papules, grouped | No caseation, no AFB | **High-Yield:** The combination of **punched-out ulcer + undermined edges + caseating granulomas + AFB+ + regional lymphadenopathy** is pathognomonic for scrofuloderma. **Clinical Pearl:** Scrofuloderma is the most common form of cutaneous TB in immunocompetent individuals and typically occurs as a complication of tuberculous lymphadenitis. ### Why This Patient Has Scrofuloderma 1. History of pulmonary TB (source of infection) 2. Painless ulcer with punched-out, undermined appearance (classic morphology) 3. Regional lymphadenopathy (direct extension from nodes) 4. Caseating granulomas with AFB on biopsy (confirmatory histology) [cite:Robbins 10e Ch 8]