M13.9: Arthritis, unspecified

Arthritis, unspecified (M13.9) is a condition that involves inflammation of one or more joints in the body. Although the exact cause in this unspecified variant is unclear, it generally occurs when an individual's immune system mistakenly begins to attack its own tissues, resulting in swelling, pain, and stiffness in the affected joints. Over time, such inflammation can worsen, leading to substantial discomfort and potentially causing the affected joints to lose their natural shape and alignment. Arthritis can affect any joint in the body, although it's commonly seen in the hands, knees, and hips. Symptoms of this condition often tend to progress slowly, with early-stage signs like joint tenderness or aching being common. As the condition develops, individuals may notice their symptoms becoming more persistent or a limited range of motion in the affected joints. It's also common for individuals with arthritis to experience bouts of increased disease activity, known as flares, followed by periods of relative remission where symptoms lessen.