Gout is a common form of inflammatory arthritis caused by hyperuricemia, an excess of uric acid in the blood. This metabolic imbalance causes uric acid to crystallize within joints and soft tissues, leading to sudden, debilitating flares of pain and swelling. While gout is strongly associated with the lower extremities, understanding its atypical presentations, such as in the shoulder, is important for proper diagnosis and care.
The Mechanism of Gout and Typical Locations
Gout begins with hyperuricemia, occurring when the body either produces too much uric acid or the kidneys do not excrete enough of it. When the blood becomes oversaturated, uric acid precipitates out, forming sharp, needle-shaped monosodium urate (MSU) crystals. These crystals deposit in the joint space, triggering an intense inflammatory response.
Immune cells recognize the MSU crystals and activate a pathway that releases inflammatory mediators, resulting in the hallmark symptoms of a gout attack: severe pain, redness, and warmth. The condition most frequently affects peripheral joints, such as the metatarsophalangeal joint of the big toe (podagra). The ankles, knees, and elbows are also common targets, as the lower temperature of the extremities enhances uric acid crystallization.
Gout in the Shoulder: Atypical Presentation
Gout can affect the shoulder, though this is considered an atypical presentation compared to lower limb joints. When it occurs, it may involve the main glenohumeral joint, the smaller acromioclavicular joint, or surrounding soft tissue structures. It often occurs in patients with long-standing, poorly controlled gout, but the shoulder may occasionally be the first joint affected.
A gout flare in the shoulder involves the sudden onset of severe pain that often peaks within hours. The joint becomes visibly swollen, red, and hot to the touch, with tenderness that limits mobility. In advanced or chronic cases, solid deposits of MSU crystals called tophi can form in the soft tissues around the shoulder, such as the rotator cuff tendons or bursae.
Distinguishing Gout from Other Shoulder Pain
Diagnosing gout in the shoulder is challenging because its symptoms can mimic common conditions, such as rotator cuff injuries, mechanical impingement, or septic arthritis. Mechanical shoulder pain is typically related to movement or chronic wear, while a gout flare is inflammatory, sudden, and presents with intense pain even at rest. The presence of systemic signs of inflammation, like fever or malaise, may also suggest an acute inflammatory process.
The gold standard for a definitive diagnosis is joint aspiration (arthrocentesis). A physician draws a sample of synovial fluid from the affected joint, which is then examined under a polarized light microscope to look for the presence of negatively birefringent MSU crystals. While blood tests can measure serum uric acid levels, they may be normal during an acute attack and are not sufficient for a conclusive diagnosis. Imaging studies, such as ultrasound, can also be used to visualize crystal deposits, sometimes revealing a characteristic “double contour sign” on the joint cartilage.
Treatment and Long-Term Management
The treatment of gout focuses on resolving the acute flare and preventing future attacks. Acute pain and inflammation are typically managed with medications like nonsteroidal anti-inflammatory drugs (NSAIDs), such as indomethacin, or the anti-inflammatory medication colchicine. Corticosteroids, administered orally or injected directly into the shoulder joint, are also effective for rapidly reducing inflammation during a flare.
Long-term management focuses on reducing the body’s overall uric acid burden through urate-lowering therapies (ULTs). Medications like allopurinol or febuxostat work by blocking the enzyme responsible for uric acid production. The goal of ULT is to maintain serum uric acid levels below 6 mg/dL, and often below 5 mg/dL if tophi are present, to dissolve crystal deposits over time and prevent joint damage. Patients beginning ULT are often prescribed a prophylactic course of colchicine or low-dose NSAIDs for several months to suppress inflammation and prevent flares that can occur as uric acid levels begin to change.