31st January 2024

Articular vs Extra-articular Manifestations

Extra-articular manifestations of gout present as gouty tophi. These are subcutaneous concentrations of urate crystals. These appear as white deposits of a chalk-like substance beneath the skin. Tophi can occur without previously having an acute attack of gout and do not typically cause pain. Common sites for tophaceous deposits include:

• The pinna of the ear. 
• The Achilles tendon
• The pulp of the fingers
• The olecranon bursa. This can give the appearance of rheumatoid nodules, so careful history and examination of the patient are needed.

Another extra-articular feature of gout are renal calculi. These form due to uric acid salt deposition within the renal matrix. Low urinary pH increases the risk of uric acid stones and nephrolithiasis. Stone formation is an important cause of renal failure and should be considered and the risk reduced. 

Complications of Hyperuricaemia

In addition to renal impairment, studies have shown that uric acid levels are independent risk factors for cardiovascular disease and associated mortality, particularly in those with hypertension and diabetes mellitus. This is related to oxidative stress caused by raised urate levels and inflammatory changes in the vasculature and is supported by urate-lowering therapies, such as allopurinol, resulting in improved cardiovascular outcomes.

The inflammatory process, when triggered within blood vessels, causes damage to the endothelium. Attempts to repair the damage results in fatty plaque deposits within the blood vessels, causing atheroma formation. This contributes to hypertension, which in turn increases blood vessel damage. Studies have shown that individuals with obesity but without metabolic syndrome have increased risk of diabetes and hypertension with raised serum urate levels. This is also true of lean individuals. 

Image Source: Wikimedia Commons (2014). Tophaceous gout, Licensed under a creative commons licence. Available for free at:  https://commons.wikimedia.org/wiki/File:Tophaceous_gout.jpg (Accessed: 30 April 2022).

Pseudogout often has a more insidious course, and symptoms may take longer to reach maximum debilitation during each flare, and there is often a longer recovery period. It is not uncommon for larger joints to be affected by pseudogout, such as knees.