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We here describe, for the first time, the development of unusually large synovial cysts, from the disproportionately small sternoclavicular joints, in a 58 year old man, with a 27 year history of severe, seropositive, erosive, destructive, deforming, nodular RA. Over the years he had been treated, albeit erratically, with several disease modifying antirheumatic drugs (DMARDs), but he had been poorly followed up.
Seven months ago, while receiving d-penicillamine 500 mg/day and methylprednisolone 2 mg/day, he presented with a 10 cm long and 5 cm thick, fluctuant, non-tender, sausage-like mass over the right clavicle, and a smaller one, about 5 cm long over the left clavicle, developed gradually over one month. Routine haematology and biochemistry were normal. A purified protein derivative (PPD) skin test was negative.
A chest computed tomomographic (CT) scan (fig 1A) showed sclerosis and subchondral and marginal erosions in the manubriosternal and both sternoclavicular and first costosternal articulations. The posterior sternal surface was largely eroded, and the cancellous portion transformed to a smooth walled cavity, filled up with soft tissue. The overlying anterior thoracic wall soft tissues contained several cystic lesions, 1–6 cm in diameter, arranged parallel to the two lateral sternal borders. The four upper costovertebral joints (not shown) were similarly affected. Paracentesis of the right mass yielded a turbulent dark yellow fluid, with white blood cells (WBCs) 40.5×109/l (82% polymorphonuclear cells (PMNs)), sugar of 80 mg/l and no malignant cells. Direct stains and cultures for common and acid fast bacteria and fungi were negative. An open biopsy of the wall of the mass on the right showed granulomatous fibrous tissue, with no evidence of malignancy and negative culture. After a repeat paracentesis with similar results, three months later, an injection, with a long acting corticosteroid preparation, of both masses was performed. Two months later, the left mass disappeared and that on the right was significantly reduced, confirmed by a second CT scan (fig 1B). This scan disclosed further excessive destruction of the left glenohumeral joint and a 6 cm synovial cyst, just anteroinferior to that, under the left upper thoracic muscles. A magnetic resonance imaging (MRI) scan confirmed, additionally, that the cysts contained only fluid, whereas their walls showed enhancement after the administration of paramagnetic medium, suggesting active inflammation (figures not shown). Furthermore, MRI showed that the soft tissue eroding the upper part of the sternum had broken into the anterior mediastinum, in close contact with the anterior pleura. Although the whole area was examined meticulously by MRI, in more than two planes, no communication of the cysts with the proximal or remote joints was demonstrated.
The synovial origin of the described lesions was strongly supported by (a) their cystic nature confirmed by CT and MRI; (b) the inflammatory character of the fluid they contained; (c) the exclusion of any infectious or malignant process; (d) the biopsy of the cystic wall, typical for synovial cyst; (e) the favourable response to the local steroid injection. Interestingly, imaging did not succeed in demonstrating any communication between the cysts and the sternoclavicular or the upper costosternal joints, a feature which even arthrography may not disclose. Nevertheless, the arrangement of the cysts along the sternal borders, and their close proximity to the severely affected sternal joints, led us to presume that they originated in the latter.
This unusual case emphasises the possibility of synovial cyst formation from any inflamed rheumatoid joint, no matter how small it may be, and the fact that such presentations may appear in very atypical locations, posing important and sometimes difficult diagnostic problems.
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