Table 2.

Descriptions of conditions that should be included in the differential diagnosis for gout.

Condition	Description of skeletal involvement	References
Gout	Asymmetric erosive arthritis that primarily affects the peripheral joints. Although rare, skeletal changes can also be present in the axial skeleton. Lesions are well-defined and are ‘scooped-out’ in appearance, often with a thin, overhanging, hook-like sclerotic margins. The first metatarsophalangeal joint is commonly affected but any joint can be affected.	Ortner (2003), Rogers et al. (1987), Rothschild and Heathcote (1995)
Rheumatoid arthritis	An autoimmune disorder of unknown aetiology that causes symmetrical erosive polyarthritis that most often affects the synovial joints of the appendicular skeleton including the small joints of the hands and feet. Most commonly the metacarpophalangeal joints and the metatarsophalangeal joints and the proximal interphalangeal joints are affected, but the distal interphalangeal joints are rarely affected. Ankylosis of joints in the hands and feet can occur in severe cases.	Rogers et al. (1987), Ortner (2003), Waldron (2019)
Erosive osteoarthritis	Asymmetrical arthropathy that produces both proliferative and erosive changes along with ankylosis. Metacarpals as well as proximal and distal interphalangeal joints of the hands are most commonly affected. Other joints are rarely affected.	Rogers et al. (1987), Waldron (2019)
Psoriatic arthritis	An asymmetric erosive arthritis associated with psoriasis, which is usually negative for rheumatoid factor. Commonly affects four joints or fewer. The involvement of the spinal joints and sacroiliac joints is typical and enthesopathy is common. Erosive lesions in the distal interphalangeal joints of the hands are common and these lesions are often accompanied by proliferative lesions located at erosion margins. The “pencil-in-cup” deformity (when the tip of a bone becomes pointed like a pencil) of the distal interphalangeal joints is characteristic.	Rogers et al. (1987), Rogers (2000), Sudoł-Szopińska et al. (2016), Waldron (2019)
Reactive arthritis	A form of reactive arthritis that occurs in reaction to an infection by certain bacteria elsewhere in the body. Sacroiliac involvement (bilateral or unilateral) is common and paravertebral bridges may cause spinal fusion with skip lesions. Asymmetrical erosive changes to the small joints can occur in the feet and less commonly, the hands. Erosion of the metatarsophalangeal joints and of the metatarsal heads is relatively common. Lanois deformity can occur in the feet.	Waldron (2019), Martel et al. (1979)
Hallux valgus	Hallux valgus is lateral angulation of the great toe. Inflammation at the insertion of the metatarsophalangeal collateral ligaments and sesamoid ligaments can trigger lytic cavitating lesions on the medial side of the metatarsal head. Characteristics of hallux valgus include: laterally angulated first metatarsophalangeal joint surface, a ridge on the medial side of the distal articular surface, degenerative changes to the distal articular surface and/or sesamoid bones. Lesions on the medial aspect of the head tend to have rounded margins and do not affect the articular surface of the first metatarsophalangeal joint.	Mays (2005)