Anastomoses of transverse tubules with terminal cisternae in polymyositis

Abnormal transverse or T tubules spatially continuous with sarcoplasmic reticulum (SR), as visualized with a lanthanum (La) tracer, were found in biopsy specimens from nine patients with polymyositis whose serum enzyme (creatine phosphokinase [CPK]) levels were elevated before the time of biopsy. On comparison with the T system in more than 50 control subjects without CPK elevation, it became apparent that presumed anastomoses of T tubules with SR were the most consistent anatomical correlates of the enzyme leakage. Two types of anastomoses were seen on the basis of passage of La: first, early segmental dilation of T tubules and perpendicular continuations with SR; and second, focal proliferation of T tubules forming "T tubule networks" and then anastomosing with SR at the periphery of the networks. The latter is considered to be a concurrent repair process for the injured triads. Lanthanum did not penetrate freely through the plasma membrane of necrotized muscle fibers. It is concluded that junctional sites between T tubules and SR may be the primary sites of leakage of sarcoplasmic enzymes in polymyositis.