Differential Diagnosis of Polyarticular Arthritis.

Polyarticular arthritis is commonly encountered in clinical settings and has multiple etiologies. The first step is to distinguish between true articular pain and nonarticular or periarticular conditions by recognizing clinical patterns through the history and physical examination. Once pain within a joint or joints is confirmed, the next step is to classify the pain as noninflammatory or inflammatory in origin. Noninflammatory arthritis, which is mostly related to osteoarthritis, has a variable onset and severity and does not have inflammatory features, such as warm or swollen joints. Osteoarthritis usually presents with less than one hour of morning stiffness and pain that is aggravated by activity and improves with rest. A review of systems is usually negative for rashes, oral ulcers, or other internal organ involvement. In contrast, inflammatory arthritis generally causes warm, swollen joints; prolonged morning stiffness; and positive findings on a review of systems. Once inflammatory arthritis is suspected, possible diagnoses are sorted by the pattern of joint involvement, which includes number and type of joints involved, symmetry, and onset. The suspicion for inflammatory arthritis should be confirmed by the appropriate serologic/tissue and/or imaging studies in the clinical setting or in consultation with a subspecialist.