Tophaceous gout

Clinical History

A 48-year-old male with a history of gout presents to the emergency department after falling off his truck. The patient reports pain in his right ankle and foot. He has swelling and tenderness of the right lateral malleolus, right fourth metatarsophalangeal joint, and distal fibular tenderness.

Imaging Findings

Anteroposterior radiograph of the right ankle reveals tophi and resulting soft tissue oedema overlying the lateral malleolus. The soft tissue oedema is due to interleukins such as IL-1, and inflammation as a result of monosodium urate crystals. Inflammatory mediators attract macrophages and neutrophils to perpetuate the inflammation and soft tissue oedema.
Lateral radiograph of the left elbow reveals tophi and nonspecific soft tissue prominence overlying the olecranon with findings favouring olecranon bursitis.
Posteroanterior radiograph of the right hand reveals tophi and resulting significant soft tissue oedema overlying the right fifth metacarpophalangeal joint. No fracture is present.

Discussion

Gouty arthritis manifests as excessive generation or inadequate degeneration of uric acid. As the production of uric acid exceeds the ability of xanthine oxidase to remove it, uric acid can saturate the blood and lead to the formation of monosodium urate crystals [1]. The monosodium urate crystals may gradually deposit around the joint in the articular cartilage and ligaments thereby causing an acute, painful arthritis or slowly destroying the cartilage [2]. The destruction of cartilage leads to erosion. Cartilage destruction and calcium salts combine with crystalline uric acid and results in tophus formation. Tophaceous gout is therefore a chronic process and defines advanced disease [3].
Patients present with painful swelling and erythema of the affected joint. Several joints may be involved as tophaceous gout may be polyarticular. The most common joint involved in gout is the first metatarsophalangeal joint of the foot, also known as podagra. On rare occasion, the urate tophi may be found in the intradermal layer of the skin of the inner thighs, shins, and forearms. This presentation is known as miliarial gout [4]. The erosions typically seen on radiographs of patients with gout are juxta-articular and located in the joint margins and lead to the classic finding of an overhanging osseous formation [5]. Soft tissue oedema is usually present due to inflammatory interleukins and macrophages and joint space is maintained.
Treatment of gout includes antihyperuricemic medications such as probenecid, losartan, allopurinol, or febuxostat [6]. The patient was given allopurinol, a xanthine oxidase inhibitor, in order to decrease the rate of generation of uric acid. Successful management of gout attacks depends mostly on patient compliance with dietary and lifestyle changes along with urate-lowering medications.
If tophaceous gout is clinically suspected, imaging studies along with synovial fluid analysis with gram stain, culture and polarizing light microscopy to examine for crystals may be useful. MRI T1-weighted images will demonstrate intermediate intensity of tophaceous deposits but findings are variable on T2 images [7]. The imaging modality of choice is ultrasound or dual-energy CT [8]. Ultrasound may reveal urate crystal deposition within the cartilage which is known as the starry sky appearance or the double contour sign. However, calcium pyrophosphate crystals cannot be differentiated from urate crystals on ultrasound. Dual-energy CT is able to demonstrate urate crystals in a different colour than surrounding structures and is therefore argued to be more specific than ultrasound.

Differential Diagnosis List

Final Diagnosis

Tophaceous gout

URL:	https://www.eurorad.org/case/14148
DOI:	10.1594/EURORAD/CASE.14148
ISSN:	1563-4086