Early biomarkers of joint damage in rheumatoid and psoriatic arthritis

Table 1 Radiological features that distinguish between rheumatoid arthritis and psoriatic arthritis

Disease feature	Rheumatoid arthritis	Psoriatic arthritis	Imaging technique	Reference
Number of erosions	+++	+	X-ray	[18]
	+++	+++	μCT	[82]
Severity of erosions	+++	++	μCT	[83]
Shape of erosions
Ʊ	+	+++	μCT	[83]
Tubule	+	+++	μCT
U	+++	+	μCT
Erosion distribution	Preponderance for radial sites	Evenly distributed	μCT	[83]
DIP joint erosion	–	+++	US, MRI, X-ray	[84]
Number of osteophytes	+	+++	μCT	[82]
Severity of osteophytes (size)	+	+++	μCT	[82]
Bone proliferation	+	+++	US, MRI, X-ray	[84]
Inflammatory changes
Synovitis	+++	++	MRI, US	[84]
Tenosynovitis	+++	++	MRI, US	[84]
Enthesitis	+	+++	MRI, US	[85]
Dactylitis	–	+++	US, MRI	[86]
Mutilans (erosions on both sides of joints)		+	X-ray	[87]

Disease features present in RA and PsA and the radiological imaging technique used to measure the feature. The number of erosions observed in RA appears to be greater than that in PsA. However, more sophisticated higher resolution techniques reveal this is not accurate because erosions in PsA are generally smaller and their detection requires these more sensitive techniques. Hence, μCT reveals a comparable extent of bone erosion in RA and PsA. MRI and US capture differences in sites affected by inflammation in these disorders. In PsA it is the enthesis that are major sites of inflammation, whereas in RA the synovium becomes chronically inflamed. Inflammation of the tendons is also prevalent in both disorders although more severe in RA. Distinct features of PsA include bony proliferation, and dactylitis. DIP, distal interphalangeal; μCT, micro computational tomography; MRI, magnetic resonance imaging; PsA, psoriatic arthritis; RA, rheumatoid arthritis; US, ultrasound

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