Purines are part of the structure of nucleic acids, molecules that make up DNA. They're present in every cell in the human body. When purines break down, they form uric acid, a waste product normally excreted by the kidneys. Gout is a condition that results from a buildup of uric acid in the body. Uric acid forms sharp crystals that gather in the joints. Though less often involved than the joints of the foot, ankle and knee, the shoulder can be affected by gout.
The sharp structure of uric acid crystals can irritate the soft tissues of a joint that has been affected by gout, causing pain. In some cases, these crystals can become so prevalent that they can lend the joint a spiky appearance upon X-ray, a condition referred to by researchers as porcupine shoulder. Pain associated with gout can be throbbing, crushing and excruciating, according to MedlinePlus. It comes on suddenly, most often in the middle of the night, and can be so severe that even the pressure of a bed sheet on the affected joint can cause extreme pain.
Gout causes inflammation in the joint, which can manifest in symptoms such as redness and swelling, according to FamilyDoctor.org. Swelling occurs when the body floods an irritated area with histamines, which increase permeability in the blood vessels. This allows increased amounts of fluids to flow out of the blood vessels and into the tissues of the affected area.
When gout has reached a chronic stage, the patient may experience the formation of tophi, knobby crystalline lumps that gather beneath the skin of the affected joint. Tophi are typically painless but can cause pain if they interfere with joint function.
Drainage of chalky material from the tophi may occur. Orthopedic surgeon Sean T. O’Leary reports that tophaceous gout in the muscle of the shoulder is far less common than pseudogout affecting the same joint. Pseudogout presents with symptoms similar to gout but is caused by a calcium deposits rather than uric acid.
Limited Range of Motion
Gout is a form of arthritis, and the New York Times notes that untreated, persistent gout can result in a deterioration of the joint structure. This can lead to deformities and decreased range of motion in the shoulder joint. O’Leary adds that rotator cuff tophi were determined to cause impingement of the shoulder joint, with subsequent decreases in all shoulder-related ranges of motion.