This is the first study to demonstrate that HRUS detects significantly more erosions than x ray in the 1st MTPJs of patients with gout, and that pathological findings can occur in clinically silent joints. It also describes sonographic findings in the 1st MTPJs that may represent changes of gout.
Previous reports, in other inflammatory joint diseases, have also demonstrated the ability of HRUS to detect more erosions than conventional x
The high spatial resolution and multiplanar capability of the technique make it particularly suitable for this purpose. Conventional x
ray will only detect erosions that are in a plane that is tangential to the radiographic beam. Variations in film projection and penetration may further limit the quality of the x
ray image, which ultimately relies upon the projection of a three dimensional image on to a two dimensional medium.14
Only the standard posteroanterior and lateral x
rays of the MTPJs were used in this study. This may have led to underestimation of the ability of plain radiography to detect erosions, but this is an accurate reflection of everyday clinical practice.
Some studies have used MRI as the “gold standard” for imaging small joints.7,15
MRI is becoming more widely available for this purpose, but it does have certain limitations when used to detect small bony erosions. MRI cannot visualise the bone cortex directly and if marrow oedema is present, a volume‐averaging effect can lead to difficulty in interpretation. Sonography has superior spatial resolution to MRI and some or all of these factors may explain some reports showing that HRUS is superior to MRI in the detection of smaller erosions in both hands and feet.8,15
We did not use MRI, as the routine use of MRI for imaging of MTPJs in patients with chronic gout is rare because of the expense and time required. Others would suggest that CT should be the “gold standard” when detecting small‐joint bone erosions. Although there has been no direct comparison between HRUS and CT in the detection of small‐joint bone erosions, HRUS has been shown to be superior to CT in the detection of erosions on larger bones.16
Nevertheless, further studies should be conducted using MRI or CT to confirm our findings. One disadvantage of HRUS is the inability to fully blind the sonographer to the diagnosis, as visual clues from the gross presentation and levels of joint tenderness can be elicited when placing the probe on the joint.
There are very few reports on the sonographic features of gout in both joints and soft tissues. Filippucci et al17
showed the potential benefit of HRUS in the monitoring of patients with gout, whereas others have described case reports of gouty tenosynovitis, rotator cuff lesions, upper‐limb cellulitis and tendon tophi.18,19,20,21
Gerster et al22
looked at the knee joint in four patients with gout and compared CT, MRI and sonography for imaging tophaceous deposits. They concluded that CT was the best modality for imaging gouty tophi.
In the current literature, there are very few reports concerning the differences found on HRUS in different arthritides.23
In our study, there were non‐specific pathological findings (eg, bone erosions, joint effusion, synovial hypertrophy and hyperechoic spots). However, sonographic findings suggesting the presence of tophus or double contour were significantly more frequent in patients with gout than in either of the control groups. The presence of these sonographic findings in the 1st
MTPJs may represent changes due to gout and could be a useful clinical tool in differentiating gout from other inflammatory arthritides. However, further studies are needed to ascertain the pathology underlying these sonographic findings.
The decision to introduce hypouricaemic therapy for chronic gout usually depends upon the frequency of gouty attacks as well as the presence of radiographic erosions and/or tophaceous deposits. Generally, it is accepted that hypouricaemic therapy should be life long with the goal of reducing and eventually eliminating gouty attacks, thereby stopping further joint destruction.24
As expected, we demonstrated a positive correlation between the number of attacks of gout in the 1st
MTPJ and the presence of erosions, but the association between the two was weak. This indicates that other factors, other than clinical attacks, must be important predictors of joint damage. This conclusion is supported by the fact that we found evidence of erosive joint damage in MTPJs that patients recalled never having been subjected to an attack of gouty arthritis. These sonographic findings in clinically silent joints have parallels with a recent study of renal tract sonography in urate nephropathy. This showed a higher than expected incidence of urolithiasis in asymptomatic patients with gout when sonography was compared with clinical signs and symptoms alone.25
In our study, there could be a bias towards patients not recalling an attack of gout in the 1st
MTPJ. However, owing to the extreme pain and discomfort often associated with acute gout in the 1st
MTPJ, inaccurate patient recall would be minimal.
Tophaceous deposits become clinically apparent only after a long period of asymptomatic hyperuricaemia.24
If one could detect tophi at a much earlier stage of the disease, this could lead to a more timely therapeutic intervention and the prevention of joint and other organ damage. x
Rays cannot be relied upon for the early detection of urate deposits in soft tissues, whereas HRUS can quickly (approximately 5 min per MTPJ in this study) and accurately detect soft‐tissue pathology.26
Furthermore, in our patients with gout, there was a high prevalence of sonographic features suggestive of intra‐articular tophi, as well as enhancement of the superficial margin of the articular cartilage (the double contour sign). These findings were infrequent in both control groups. Four disease controls appeared to exhibit the sonographic features of soft tophus‐like deposition, but this may reflect the propensity for soft tophi to be confused with extensive synovial hypertrophy.
The introduction of biological treatments for rheumatoid arthritis and other inflammatory arthritides27
has placed an obligation on rheumatologists to detect these diseases early in order to reduce joint damage by aggressive and more targeted treatment.28
To this end, the use of HRUS by rheumatologists is increasing rapidly to aid with early detection of synovitis and erosions in these patients. The same paradigm should be applied to the management of gout. New treatments to aid with uric acid suppression are currently being developed,29,30
and the ability to detect joint damage and tophaceous deposition at an early stage using HRUS should allow earlier and more timely intervention.
HRUS may assist with the management of gout in two ways: first, by aiding in the diagnosis by identifying sonographic features that may be representative of the disease, and, second, by allowing the early detection of erosive joint damage and/or tophaceous deposits even in clinically silent joints. Both require further studies.