A persistent infection of enteroviruses and cardioviruses has been implicated in polymyositis and dermatomyositis, but conventional hybridisation studies of the presence of enterovirus RNA and encephalomyocarditis (EMC) virus RNA in affected muscle have yielded conflicting results. To investigate further the possibility of viral persistence, the presence of viral RNA in muscle from patients with adult onset polymyositis and dermatomyositis was investigated using a polymerase chain reaction (PCR) technique.
Muscle tissue was obtained from 10 patients with polymyositis and five patients with dermatomyositis, all with adult onset active disease. A PCR was performed using primers with high specificity for enterovirus and EMC virus RNA, followed by Southern blot hybridisation with an oligonucleotide probe directed against the internal portion of the amplified product. A PCR directed against the Abelson tyrosine kinase mRNA served as an internal control for the presence and quality of RNA.
A specific amplification for enterovirus or for EMC virus could not be seen in any of the muscle biopsy samples, despite a sensitivity of about 30 plaque forming units for enterovirus and of 100 plaque forming units for EMC virus. Southern blot hybridisation confirmed these results in that positive controls hybridised with the oligonucleotide probe, but no signal was obtained with the muscle specimens.
A sensitive and specific PCR technique showed no evidence of the presence of enterovirus or EMC virus RNA in muscle samples from patients with polymyositis or dermatomyositis. These data do not support the proposal that viral RNA persistence plays a part in these idiopathic inflammatory myopathies.