A Rare Paradoxical Reaction in Cutaneous Tuberculosis: Insight from a Case of Lupus Vulgaris.

Introduction: Lupus vulgaris (LV) is the most common form of paucibacillary cutaneous tuberculosis (TB), which is treatable with antituberculosis treatment (ATT). Otherwise, paradoxical reaction (PR) is an adverse clinical consequence of restoring the specific antigen immune response elicited by ATT. Case Presentation: We report a case of PR in a 20-year-old female patient with LV, who had previously completed treatment for meningitis and lymphadenitis TB and had a history of juvenile idiopathic arthritis (JIA). Initially, the patient presented with reddish papules on the neck, which appeared four months before consultation. The skin lesions progressively enlarged and failed to heal completely despite treatment, accompanied by knee joint pain. Physical examination revealed well-defined reddish-brown plaques measuring 1.5×1×0.1 cm on the neck and 5×3×0.5 cm beneath the right chin with gyrate borders. Diascopy tests revealed an "apple jelly" sign, while dermoscopy demonstrated yellowish-white globules on a pinkish-red background. Histopathological examination revealed tuberculoid granulomas, Langhans giant cells, and epithelioid cells with caseous necrosis. Based on these findings, a diagnosis of LV was established. However, bacteriological culture and polymerase chain reaction (PCR) testing showed no evidence of Mycobacterium tuberculosis. After three weeks of category I ATT, the skin lesions worsened and enlarged, suggesting the development of PR. The lesions subsequently improved two weeks after initiating additional therapy with 8 mg methylprednisolone twice daily and showed significant improvement following the addition of 200 mg hydroxychloroquine once a day. Conclusion: Although PR is rare, it should be considered in patients who demonstrate clinical deterioration after ATT. Clinicians should be aware of its occurrence in cutaneous TB, particularly LV, to ensure timely recognition and appropriate management.