Often presents as erythematous plaques with slivery scaling (plaque psoriasis)
Signs and symptoms
Lesions mainly found on extensor surfaces (knee and elbow joints)
Nail pitting and onycholysis common
Lesions may be found along areas of recent trauma (Koebner phenomenon)
Guttate psoriasis (predominantly < 1cm drop-shaped lesions) are commonly associated with Group A Streptococcal infections (pharyngitis, tonsilitis etc.)
Psoriatic arthritis found in approx. 30% of patients with psoriasis. It is one of the seronegative spondyloarthritic disorders. Often present with pencil-in-cup appearance of affected digits.
Seronegative Arthritis
PAIR:
Psoriatic arthritis
Ankylosing spondyloarthritis
Inflammatory bowel disease
Reactive arthritis
NB: These are rheumatoid factor negative (hence the name) but often HLA B27 positive
Investigation
Usually a clinical diagnosis
Skin biopsy may show thickened (hyperplastic) epidermis, parakeratosis (nuclei preserved in the stratum corneum) and Munro microabscess (neutrophilic infiltration of the stratum corneum without infection).
Management
Mild: topical steroids, topical vitamin D (calcipotriene), topical vitamin A (retinoids)
Severe disease and/or presence of arthritis: immunomodulation such as methotrexate, anti-TNF α and anti-interleukins agents, UV light therapy