Table 3.

Description of lesions observed on individuals from Cambridge and differential diagnosis.

PSN	Age and Sex	Affected elements	Description of Lesions	Differential diagnosis	Final Diagnosis
42	Middle adult male	Left first metatarsal	Well-defined, cavernous lytic lesion with thin, overhanging sclerotic margins present on the medial aspect of the head, adjacent to the joint surface (Fig. 4a, c). The distal joint surface is laterally deviated with an anterolateral extension of the joint surface (Fig. 4b, f, indicated by grey arrow). There is also a ridge on the distal articular surface of the head, located approximately 3 mm from the medial margin of the articular surface (Fig. 4f, indicated by white arrow).	The observed lesions are symmetrical, but only the medial aspects of the heads of the first metatarsals are affected. This distribution is inconsistent with rheumatoid arthritis. There are no proliferative changes or ankylosis present so unlikely to be erosive osteoarthritis. There is no involvement of the sacroiliac joints or spine, therefore it is unlikely to be psoriatic arthritis and is less likely to be reactive arthritis. The ridges on the distal articular surface of each metatarsal are consistent with lateral deviation of the first proximal pedal phalanx.	Both gout and hallux valgus
		Right first metatarsal	Well-defined, cavernous lytic lesion with thin, overhanging sclerotic margins present on the medial aspect of the head, adjacent to the joint surface (Fig. 4e). The distal joint surface is laterally deviated (Fig. 4d and there is a ridge located on the distal articular surface of the head, located approximately 2−3 mm from the medial margin of the articular surface.
93	Mature adult male	Left first metatarsal	Large, scooped-out lytic lesion with thin overhanging sclerotic margins located on the medial aspect of the head. The lesion is primarily located adjacent to the joint surface, but some of erosion of the medial aspects of the articular surface with signs of overlying taphonomic damage is present (Fig. 3b). New reactive bone formation surrounds the lesion.	The distribution of the lesions is symmetrical, but lesions are only present in the feet. This is uncommon with rheumatoid arthritis and erosive osteoarthritis, which more commonly affect the hands. The sacroiliac joints are not affected, but vertebral fusion is present (see below). Psoriatic arthritis and reactive arthritis are considered below.	Gout
		Right first metatarsal	Scooped-out lytic lesions with sclerotic margins that have coalesced located on the medial aspect of the head with evidence of erosion of the medial and dorsal aspects of the articular surface.
		Right first proximal pedal phalanx	Multiple scooped-out lytic lesions with sclerotic margins that have coalesced present on the medial aspect of the head with evidence of erosion of the medial and planter aspects of the articular surface (Fig. 3b).
		Right first distal pedal phalanx	Well-defined scooped-out lytic lesion with thin overhanging margins located on the dorsal margin of the proximal articular surface.
		Thoracic vertebrae	T6-9 ankylosed with extensive bone proliferation located on the right side of the vertebral column. These are ‘dripping candle wax’ in appearance. T10 also has adhering bone proliferation present on the right aspect of the vertebral body but remains unfused. The vertebral disc space is preserved. No sacroiliac involvement.	The preserved joint spaces and ‘dripping candle wax’ ossifications that are found exclusively on the right side of the affected vertebra is diagnostic of DISH. There is no evidence of sacroiliac joint fusion and the morphology of the changes is inconsistent with ankylosing spondylitis, reactive arthritis and psoriatic arthritis.	DISH
522	Old adult male	Right first metatarsal	Multiple scooped-out lytic lesions with sclerotic margins that have coalesced resulting in significant erosion to the medial aspect of the head and the distal articular joint surface (Fig. 2).	The distribution of lesions is symmetrical but confined to the pedal elements. There is no evidence of erosive lesions in the joints of the hands or elsewhere in the skeleton. This distribution of lesions observed here is uncommon in rheumatoid arthritis as the distal phalanges tend to not be affected. There are no proliferative changes, so it is unlikely to be erosive osteoarthritis. There is no involvement of the sacroiliac joints or spine, so it is unlikely to be psoriatic arthritis or reactive arthritis. The distribution and erosive nature of the lesions is inconsistent with hallux valgus.	Gout
		Left first metatarsal	Multiple scooped-out lytic lesions with sclerotic margins that have coalesced located on the medial aspect of the head. The distal articular surface has been affected on the medial and planter aspects (Fig. 3a).
		Right first proximal pedal phalanx	Well-defined, erosive lesions with sclerotic margins on the dorsal surface of the element, immediately adjacent to the proximal articular surface.
		Right first distal pedal phalanx	Small (2 mm in diameter), scooped-out lytic lesion with overhanging, sclerotic margins located on the dorsal aspect immediately adjacent to the proximal articular surface.
		Right 5th metatarsal	Multiple scooped-out lytic lesions with thin, overhanging, sclerotic margins that have coalesced resulting in substantial damage to the lateral aspect of the head and the lateral border of the lateral aspect of the distal articular surface.
		Left 5th metatarsal	Multiple scooped-out lytic lesions with thin, overhanging, sclerotic margins that have coalesced resulting in substantial damage to the lateral aspect of the head and the lateral border of the distal articular surface (Fig. 3a).
		Right pedal sesamoid bone (x2)	Multiple scooped-out lytic lesions with sclerotic margins that have coalesced resulting in substantial damage to the elements (Fig. 3a).
523	Young adult male	Right first distal pedal phalanx	Well-defined, scooped-out lytic lesion with sclerotic margins present on the dorsal aspect of the element, immediately adjacent to the proximal articular surface (Fig. 3d).	Only one joint is affected which is inconsistent with the distribution of rheumatoid arthritis. There are no proliferative changes, so it is unlikely to be erosive osteoarthritis. Nor is there involvement of the sacroiliac joints or spine, thus it is unlikely to be psoriatic arthritis or reactive arthritis.	Gout
535	Adult, sex unobservable	Right intermediate pedal phalanx	Scooped-out lytic lesions with overhanging, sclerotic margins that has resulted in the destruction of much of the lateral and planter aspect of the shaft. The lesion is located adjacent to the proximal joint surface (Fig. 3c).	The asymmetrical distribution of lesions in the feet is inconsistent with rheumatoid arthritis. There is no involvement of the sacroiliac joints or spine, thus unlikely to be psoriatic arthritis or reactive arthritis. There are no proliferative lesions associated with the erosive lesions, so it is unlikely to be erosive osteoarthritis.	Gout
		Right first metatarsal	Well-defined lytic lesions with sclerotic margins on the medial aspect of the head, located adjacent to the distal articular surface. There is also a ridge on located approximately 3 mm from the medial margin of the distal articular surface.
		Left first metatarsal	There is a ridge located approximately 2 mm from the medial margin of the joint surface on the distal articular surface.		Hallux valgus
797	Middle adult female	Right first metatarsal	Well-defined, scooped-out lytic lesion with overhanging, sclerotic margins present on the medial aspect of the head, located immediately adjacent to the distal articular surface.	The asymmetrical distribution of the lesions is inconsistent with rheumatoid arthritis. There is no involvement of the sacroiliac joints or spine, thus unlikely to be psoriatic arthritis or reactive arthritis. There are no proliferative lesions associated with the erosive lesions, so it is unlikely to be erosive osteoarthritis.	Gout
		Right first distal pedal phalanx	Well-defined, scooped-out lytic lesion with overhanging margins, located on the medial aspect of the proximal articular surface. The lesion is primarily located on the joint margin, but the proximal articular surface is also affected.