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Anti-Signal Recognition Particle Autoantibody Not Specific Only For Polymyositis

Anti-signal recognition particle (SRP) autoantibody remains specific for polymyositis but is also detected in patients without polymyositis with other immunologic syndromes, report researchers from the United States.

Anti-SRP autoantibodies are associated mainly with polymyositis (PM), but are not frequently found in patients with other inflammatory conditions such as arthritis and Raynaud's phenomenon.

In this study, Amy H. Kao and colleagues, University of Pittsburgh School of Medicine, prospectively evaluated the long-term clinical, serologic, and pathologic features of patients with connective tissue disease (CTD) and the anti-SRP autoantibody. Patients included 134 with PM, 129 with dermatomyositis, and 790 with systemic sclerosis (SSc) or 109 with overlap syndrome. There were 16 patients with PM and SRP-positive. These patients were compared to 2 control groups of 118 patients with PM and SRP-negative: 46 patients who were synthetase-positive and 72 who were synthetase-negative. Each of these 2 groups were also compared to patients with PM and SRP-positive.

At initial evaluation, the frequency of severe proximal muscle weakness was significantly increased in the patients with PM and SRP-positive compared to the synthetase-negative control PM patients (P < .0001) and synthetase-positive control PM patients (P < .001). Muscle atrophy was also significantly more frequent at initial evaluation for the PM and SRP-positive group than for the synthetase-positive control group (P < .0001). Only 13% of the SRP-positive PM patients had cardiac involvement, and malignancy was not associated with anti-SRP. Of 6 of the 18 SRP-positive PM patients in whom swallowing studies were performed, oesophageal dysmotility was found in all 6.

Pathologic findings of muscles showed more hypertrophic myofibers in SRP-negative controls compared to SRP-positive PM (47% vs. 10%, respectively), which was not significant (P =.09). Significantly less endomysial inflammation was found in biopsy specimens from the SRP-positive PM patients compared to the SRP-negative PM patients (P = .007).

Survival rates were comparable, with an 86% 5-year cumulative rate in the SRP-positive PM patients compared to 83% and 75% in the synthetase-negative and positive controls, respectively.

The authors conclude that "although anti-SRP remains an autoantibody specific for PM, it is occasionally detected in patients with other immunologic syndromes in the absence of PM."

Arthritis Rheum 2004 Jan;50:1:209-15. "Anti-signal recognition particle autoantibody in patients with and patients without idiopathic inflammatory myopathy"

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