A 28-year-old woman from endemic area presents with a single hypopigmented macule on her arm with impaired sensation. Slit-skin smear examination is negative for acid-fast bacilli. Which investigation is most appropriate to confirm early/indeterminate leprosy?

Explanation

## Investigation of Choice for Indeterminate Leprosy ### Clinical Context: Negative SSS with Suggestive Features **Key Point:** When slit-skin smear is negative but clinical suspicion for leprosy remains high (single lesion with sensory loss, thickened nerve), histopathological examination of skin biopsy becomes the investigation of choice to confirm indeterminate or early leprosy. ### Why Histopathology is Preferred in This Scenario **High-Yield:** Histopathology: - **Detects early/indeterminate leprosy** — shows characteristic dermal infiltration and perivascular inflammation even when bacilli are sparse or absent - **Identifies granuloma pattern** — helps classify disease type (indeterminate → tuberculoid vs lepromatous spectrum) - **Provides morphological confirmation** — differentiates leprosy from other hypopigmented dermatoses - **Sensitive for paucibacillary forms** — tuberculoid and indeterminate leprosy often have negative SSS but positive histology ### Histopathological Features by Type | Leprosy Type | Histology | Bacilli in Biopsy | |---|---|---| | **Indeterminate** | Perivascular and periadnexal lymphocytic infiltrate; minimal granuloma | Sparse/absent | | **Tuberculoid (TT)** | Well-formed epithelioid granulomas; Langhans cells | Rare (0–1 per section) | | **Borderline Tuberculoid (BT)** | Multiple epithelioid granulomas; fewer than TT | Few (1–10 per section) | | **Borderline Lepromatous (BL)** | Macrophages with foamy appearance; some epithelioid cells | Numerous (100–1000 per section) | | **Lepromatous (LL)** | Sheets of foamy macrophages; no epithelioid cells | Abundant (>1000 per section) | **Clinical Pearl:** In indeterminate leprosy, the bacillary index (BI) on histology is typically 1–2+, whereas SSS may be negative because bacilli are concentrated in dermis rather than epidermis. ### Why Other Options Are Suboptimal **Repeat SSS from multiple sites:** While reasonable, repeating SSS has low yield in paucibacillary disease and delays diagnosis. Histology is more definitive. **Lepromin test:** Indeterminate leprosy may show variable lepromin positivity (weakly positive or negative). It is not diagnostic and takes 3–4 weeks. **Nerve conduction studies:** Useful for assessing nerve damage and monitoring treatment but do not confirm the diagnosis of leprosy. **Mnemonic:** **HIPS** — **H**istopathology for **I**ndeterminate leprosy with **P**aucibacillary (negative SSS) and **S**ingle lesion.