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A study of patients presenting over three years with syndromes affecting skeletal muscles has found that those with serum antibody to the signal recognition particle (SRP) represent a defined syndrome. Empirical evidence suggests that early corticosteroid treatment may improve muscle strength.
Seven patients had antibodies to SRP but no antibodies linked with other myopathies. Their age range was 32–70 years and five were women. In most patients the disease started in the autumn (August-January), and all had similar signs and symptoms—severe, rapidly increasing weakness of proximal muscles, leading to disability. Muscle strength was recorded in some proximal muscles as MRC grade 0/5 in five patients and 3/5 in two. The weakness was always greatest in the deltoid and psoas muscles. Sensation was unaffected. Creatine kinase was greatly increased, up to 3000–25 000 U/l, and active myopathy was confirmed by electromyography.
Biopsy specimens of affected muscles showed active degeneration and regeneration of muscle fibres and swollen, but sparse, endomysial capillaries containing deposits of the terminal C5b–9 components of the complement cascade. No inflammation was evident in any of the samples, marking out this syndrome from other immune myopathies.
Patients had a neuromuscular examination and biopsy of muscles of grade 4/5 strength. Frozen sections were examined by histochemical and immunocytochemical methods and compared with those from six normal controls.
Subgroups of myopathologic syndromes are starting to be recognised by their specific clinical, immunological, and pathological criteria, and some are associated with specific serum antibody, the best defined so far and most common is with anti-Jo-1.