Inflammatory Joint Disorders and Neutrophilic Dermatoses: a Comprehensive Review.

Rheumatoid arthritis and spondyloarthritis are inflammatory joint disorders with an autoimmune pathogenesis and systemic involvement. The skin is one of the most frequently affected extraarticular sites with a number of manifestations or distinct diseases, including common conditions, such as rheumatoid nodules and psoriasis, and rare diseases like neutrophilic dermatoses. The latter are clinically characterised by polymorphic lesions, including pustules, bullae, abscesses, papules, nodules, plaques and ulcers, and histologically by neutrophil-rich inflammatory infiltrates. Inflammatory joint disorders and neutrophilic dermatoses share a number of pathophysiological features related to their cytokine overexpression profile. Moreover, any organ system can be potentially involved in neutrophilic dermatoses, giving rise to the concept of neutrophilic disease. Among the extracutaneous manifestations of neutrophilic disease, joint involvement is regarded as the most common. It is not associated with erosions and disability and usually responds to treatment for skin involvement, consisting of systemic corticosteroids and, in refractory cases, immunosuppressants or biologics. Arthritis may also be the initial manifestation of rheumatoid arthritis or spondyloarthritis, which has a chronic or recurrent course and requires a continuous treatment with synthetic or biologic disease-modifying anti-rheumatic drugs. If not properly treated, they may be associated with disability and reduced quality of life. Skin lesions occurring during the course of rheumatoid arthritis and spondyloarthritis require a multidisciplinary approach envisaging the collaboration of dermatologists and rheumatologists in order to achieve early diagnosis and treatment. Several biomarkers may help the clinician in the differential diagnosis of arthritis while histology is pivotal for the correct classification of the skin disease. However, in some cases, only regular follow-up allows a definite diagnosis. In this review article, we focus on the prototypic neutrophilic dermatoses like pyoderma gangrenosum, Sweet's syndrome, hidradenitis suppurativa and their syndromic forms as well as on their articular involvement, providing a simple approach for their diagnosis and therapy.