Leprosy and psoriasis: an enigmatic relationship.

The relationship between leprosy and psoriasis has been controversial since ancient times. Based on the fundamental importance of nerve involvement in the pathogenesis of leprosy and psoriasis, it has been hypothesized that leprosy patients may be protected from developing psoriasis. There are only sporadic reports of coexistence of these two diseases as evidence of this negative association. We report a 64-year-old male patient with borderline leprosy and psoriasis. Recent advances in the elucidation of pathogenesis of both diseases have contributed to the understanding of this enigmatic relationship. Various genetic, immunological, and structural alterations in leprosy and psoriasis as discussed could be responsible for the rare co-existence of these two diseases in a given patient.