Statins can cause a necrotizing myopathy and hyperCKaemia which is reversible on 
cessation of the drug. What is less well known is a phenomenon whereby statins 
may induce a myopathy, which persists or may progress after stopping the drug. 
We investigated the muscle pathology in 8 such cases. All had myofibre necrosis 
but only 3 had an inflammatory infiltrate. In all cases there was diffuse or 
multifocal up-regulation of MHC-I expression even in non-necrotic fibres. 
Progressive improvement occurred in 7 cases after commencement of prednisolone 
and methotrexate, and in one case spontaneously. These observations suggest that 
statins may initiate an immune-mediated myopathy that persists after withdrawal 
of the drug and responds to immunosuppressive therapy. The mechanism of this 
myopathy is uncertain but may involve the induction by statins of an endoplasmic 
reticulum stress response with associated up-regulation of MHC-I expression and 
antigen presentation by muscle fibres.