Bilateral shoulder pain: psoriatic arthritis masquerading as overuse

A 25-year-old man who played summer softball developed bilateral shoulder pain. The pain was not alleviated by decreased activity, and signs and symptoms, including previous bilateral foot pain that developed before the onset of a psoriatic scalp lesion, suggested psoriatic arthritis (PA). Bilateral pain is unusual with PA; more typically, patients have monarticular pain (see "Asymmetric Presentation of Psoriatic Arthritis," below). Discussed are differential diagnosis, etiology, clinical features, and treatment, including physical therapy, NSAIDs, and disease-modifying agents such as sulfasalazine.