Lupus vulgaris (LV) is the most common form of cutaneous tuberculosis in India. Its characteristic lesion is an 'apple-jelly' nodule seen on:

• A Dermoscopy
• B Wood's lamp examination
• C Polarised light dermoscopy
• D Diascopy (pressing a glass slide on the lesion) ✓

Explanation

The 'apple-jelly' sign of lupus vulgaris is demonstrated by diascopy: pressing a glass slide firmly against the brownish-red plaque blanches the overlying blood, revealing the underlying yellow-brown ('apple-jelly' coloured) granulomatous infiltrate. This translucent granulomatous colour is due to tuberculous granulomas in the dermis. Lupus vulgaris has a high tendency to relapse, scar, and undergo malignant transformation (SCC) in longstanding untreated lesions. It is a paucibacillary (high-immunity) form of cutaneous TB.

Reference: Neena Khanna Illustrated Synopsis of Dermatology & STD, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.