Ultrasonographyc Evaluation of Metacarpophalangeal Joints Can be Useful in the Differential Diagnosis of Early Rheumatoid Arthritis and Early Spondyloarthritis. A Monocentric Preliminary Study

Background/Purpose: A number of studies have demonstrated that musculoskeletal ultrasonography (MSUS) is more sensitive in diagnosing arthritis than clinical examination although, as underlined in a recent review, it remains controversial whether it can substantially improve discrimination in the setting of early arthritis (EA). In 2011, Gutierrez et al. published preliminary data showing a high frequency of peritenon extensor tendon inflammation in patients with psoriatic arthritis (PsA), thus suggesting the potentially important role of US in the differential diagnosis of rheumatoid arthritis (RA) and PsA at metacarpophalangeal (MCP) joint level, and recommending additional research in order to confirm these data.Aim was to compare MSUS findings at MCP joint level in patients with early RA and early spondyloarthritis (SpA). Methods: We retrospectively selected 35 patients who had been definitely diagnosed as having RA (2010 ACR/EULAR criteria) or axial/peripheral SpA (2009 ASAS criteria) within one year of their first visit from a consenting cohort of EA patients attending our Rheumatology Department between November 2012 and July 2016. Their demographic, clinical data and baseline MCP/wrist MSUS assessment data were recorded during the patients’ first visit to our EA clinic by an experienced rheumatologist and a blinded experienced sonographer. All of the patients were scanned using an ESAOTE MyLAB 70 equipped with a 6-18 MHz linear array transducer, and the findings were scored in accordance with the OMERACT guidelines. Results: The MSUS data of 20 RA patients (17 females and three males; median age 59 years, range 35-83 years; median time to a definite diagnosis 2.4 months, range 1-11 months) and 15 SpA patients (nine females and six mles; median age 53 years range, 18-78 years; median time to definite diagnosis 1.7 months, range 1-8 months) were retrospectively analysed. At the time of their first visit at the EA clinic, all of the patients had at least one MCP joint with synovial fluid and/or synovial hypertrophy with a grey scale (GS) score of >1, and there were no statistically significant differences in the percentages of patients presenting at least one power Doppler(PD)-positive joint (55% of RA and 53% of SpA patients; p= 0.92) and PD-positive tenosynovitis of the flexor tendons in at least one finger (10% of RA and 33% of SpA patients; p= 0.08). There was a statistically significant difference in the percentage of patients with erosion in at least one MCP (25% of RA and 0% of SpA patients; p=0.036) and in the percentage of patients with PD-positive paratenonitis of the extensor tendons in at least one finger (30% of RA and 80% of SpA patients; p= 0.003). Conclusion: The patients with early RA showed a statistically higher percentage of erosions at the MCP MSUS evaluation of their first visit to the EA clinic than the patients with early SpA, who presented a higher percentage of PD-positive paratenonitis at the level of the extensor tendons than the patients with early RA. Larger studies are required to confirm the potential role of MCP MSUS in the differential diagnosis of early RA and early SpA.