Peripheral SpA commonly causes inflammation in joints and/or tendons outside the spine or sacroiliac joints. Commonly involved sites include joints in the hands, wrists, elbows, shoulders, knees, ankles, and feet. Inflammation of the tendons can occur in the fingers or toes (dactylitis) or where tendons and ligaments meet with bone (enthesitis). Almost all people with PsA fit into the pSpA category at some point in their disease. People with reactive arthritis, enteropathic arthritis, and undifferentiated arthritis may also fit into this category.
Many people with SpA have or will develop both axial SpA and peripheral SpA. Others will have only axial SpA or only peripheral SpA.