Patterns of abnormal protein expression in target formations and unstructured cores

Streaming of Z-disks and focal myofibrillar degeneration occur both in target formations (TF) and unstructured cores (UC). Similar myofibrillar alterations are also part of the spectrum of ultrastructural reactions that can occur in the myopathies associated with myofibrillar degeneration and abnormal foci of desmin positivity. In the latter disorders, there is ectopic overexpression of dystrophin, neural cell adhesion molecule (NCAM), gelsolin, β-amyloid precursor protein (βAPP) epitopes, α₁-antichymotrypsin (α₁-ACT), and many abnormal fiber regions are also strongly congophilic. Therefore, we searched for similar abnormalities in TF and UC. The UC and the center of TF show increased immunoreactivity for actin, α-actinin, gelsolin, dystrophin, βAPP epitopes, (α₁-ACT, β2-microglobulin, desmin, and NCAM, but minimal or no congophilia. The periphery of the TF reacts strongly for nebulin but not for actin. The observed immunocytochemical alterations in TF and UC may represent a stereotyped cellular response associated with myofibrillar degeneration due to any cause. However, the three-dimensional profile of the TF and UC as well as their fiber-type specificity distinguish them from lesions that have similar immunocytochemical profiles in other myopathies.