Periarthritis of the shoulder generally occurs in people over 40 years old, with the most common symptom being pain in the shoulder joint. Initially, there may be a soreness and pain in the shoulder, which is milder during the day and often worsens at night. The pain may intensify with changes in weather or after exposure to cold. In later stages, the pain may gradually spread around the entire shoulder joint and may involve the neck, scapular area, deltoid muscle, upper arm, or the lateral side of the forearm. Periarthritis not only causes shoulder pain, but also leads to restricted movement of the shoulder. This manifests as difficulties in simple actions that require raising the arms, such as combing hair, dressing, or scratching an itch. In advanced stages of periarthritis, there may also be muscle atrophy in the shoulder, particularly in the lateral deltoid muscle, which intensifies the movement disorders of the shoulder joint, resulting in difficulties in lifting the upper arm and extending it backward. Shoulder pain is not solely caused by periarthritis and should not be self-diagnosed. If shoulder pain occurs, it is advisable to seek medical treatment at a hospital.