Arthritis: Swelling within a joint, or limitation in the range of joint movement with joint pain or tenderness, which persists for at least 6 weeks, is observed by a physician, and is not due to primarily mechanical disorders or to other identifiable causes.
Dactylitis: Swelling of one or more digits, usually in an asymmetric distribution, which extends beyond the joint margin.
Enthesitis: Tenderness at the insertion of a tendon, ligament, joint capsule, or fascia to bone.
Inflammatory lumbosacral pain: Lumbosacral spinal pain at rest with morning stiffness that improves on movement.
Nail pitting: A minimum of 2 pits on one or more nails at any time.
Number of affected joints: Joints that can be individually evaluated clinically are counted as separate joints.
Positive test for rheumatoid factor (RF): At least 2 positive results (as routinely defined in an accredited laboratory), at least 3 months apart, during the first 6 months of disease.
Psoriasis: As diagnosed by a physician (but not necessarily a dermatologist).
Quotidian fever: Fever that rises to 39°C once a day and returns to 37°C between fever peaks.
Serositis: Pericarditis and/or pleuritis and/or peritonitis.
Sacroiliac joint arthritis: Presence of tenderness on direct compression over the sacroiliac joints.
Spondyloarthropathy: Inflammation of entheses and joints of the lumbosacral spine.
Uveitis: Chronic anterior uveitis as diagnosed by an ophthalmologist.