• Infectious arthritis. Also called septic arthritis, infectious arthritis refers to arthritis that is caused by an infection within the joint. Infectious arthritis is often caused by bacteria that spread through the bloodstream to the joint. Sometimes it is caused by viruses or fungi. Infectious arthritis can affect the shoulders. Untreated, infection can lead to joint destruction.

Learn more about septic arthritis from the National Library of Medicine.

  • Polymyositis. Polymyositis, meaning inflammation of many muscles, is one of a group of disorders characterized by inflammation and muscle weakness. The main symptom of polymyositis is symmetric weakness of the large muscles closest to the trunk. Initially, the hips, thighs and shoulders are commonly affected. The shoulder and pelvic girdle muscles are most severely affected. The weakness may make it difficult to lift heavy objects or even lift your arm to comb your hair or to put on a coat.

 

  • Dermatomyositis. Dermatomyositis is an inflammatory disease of the muscles, like polymyositis. However, dermatomyositis has a somewhat severe onset and affects both children and adults. In addition to the symptoms of polymyositis, including pain and weakness of the muscles around the shoulders and pelvis, symptoms of dermatomyositis also include a patchy skin rash, purplish discoloration of the eyelids, swelling around the eyes, changes around the nail beds and calcium deposits in the shoulders, pelvis, hips, calves and thighs, which may limit motion.

 

  • Polymyalgia rheumatica. Polymyalgia rheumatica is a rheumatic disorder characterized by pain and stiffness in the neck, shoulders and hips. It usually develops gradually but may come on suddenly. It is rare in people less than age 50, but becomes more common with age. It often resolves on its own over time.

Learn more about polymyalgia rheumatica from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS).

  • Osteonecrosis. Also called avascular necrosis, aseptic necrosis or ischemic necrosis, osteonecrosis is a disease in which a temporary or permanent loss of blood supply to the bone causes the bone to die and eventually collapse. It often occurs in a bone near the joint, which causes the collapse of the joint surface. The disease is most common in the top of the thigh bone (femur). Other common sites include the upper arms, knees, shoulders and ankles.

Learn more about osteonecrosis from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS). 

  • Lyme disease. Lyme disease is an infectious disease spread by the bite of deer ticks infected with the bacteria Borrelia burgdorferi. The first symptoms are often a bulls-eye-shaped rash and flu-like symptoms. If not treated early, the disease symptoms may progress to involvement of the heart, nervous system and joints, including the shoulder.

Learn more about Lyme disease.

  • Other diseases. Sometimes pain in the shoulders is due to causes outside the joint. Causes of pain to the shoulder are as diverse as gallstones, liver abscess, angina or heart attack, or even an ectopic pregnancy. If you experience unusual shoulder pain it is important to see a doctor to find the cause.