The Uncommon Coexistence of Mid-Borderline Leprosy and Generalized Pustular Psoriasis.

Leprosy is a chronic granulomatous disease caused by Mycobacterium leprae that primarily affects the skin and peripheral nerves, whereas generalized pustular psoriasis (GPP) is a rare and severe form of psoriasis characterized by widespread sterile pustules and systemic symptoms. Their coexistence is extremely rare due to distinct genetic, immunologic, and epidemiologic profiles. We report a case of a 28-year-old female presenting with both mid-borderline (BB) leprosy and severe GPP. She initially developed numb, erythematous patches on her extremities, followed by pustular eruptions on her right arm that became generalized. Physical examination revealed lagophthalmos, right claw hand, and glove-and-stocking anesthesia without nerve enlargement. Skin lesions included anesthetic macules and plaques on extremities, punched-out lesions on the back, and pustules with crusting and scaling on the face and extremities. A slit-skin smear showed a bacterial index of 1+, and Gram staining of pustules revealed polymorphonuclear cells without bacteria. Histopathology from punched-out lesions revealed granulomas with epithelioid cells and Langhans giant cells. Biopsy of pustules showed features consistent with GPP, including psoriasiform hyperplasia, Munro's abscesses, and Kogoj's spongiform pustules. The patient was diagnosed with BB leprosy with severe reversal reaction coexisting with GPP. She was treated with WHO-recommended multidrug therapy for multibacillary leprosy and systemic corticosteroids, leading to marked clinical improvement within 47 days. This case highlights the importance of recognizing rare coexisting conditions of leprosy and autoimmune diseases, emphasizing the need for a comprehensive diagnostic approach and prompt management to achieve favourable outcomes.