Coexistence of polyarteritis nodosa and psoriatic arthritis in a child: an unreported association: Polyarteritis nodosa and Psoriatic arthitritis.

Polyarteritis nodosa (PAN) is a non-frequent vasculitis of small- and medium-sized vessels. Psoriatic arthritis (PA) is described as a "unique inflammatory arthritis associated with psoriasis" with an inexact prevalence rate due to the lack of widely accepted classification criteria. We describe the case of an 11-year-old boy that presented with fever of unknown origin plus clinical signs of sacroiliitis, bilateral enthesitis of the plantar fascia, and skin psoriasis. He acutely developed erythematous and tender nodular lesions in the lower limbs that lasted around 3 weeks and spontaneously disappeared at the same time as the fever. He was diagnosed as having PAN and PA according to clinical and histological criteria. This is the first report of the coexistence of PAN and PA in a child indicating a possible relation (maybe cross-reactivity of an infectious agent) between PAN and spondiloarthritis.