Morphological spectrum and clinical features of myopathies with tubular aggregates.

Tubular aggregates (TAs) are aggregates of densely packed tubules in human skeletal muscle fibers with particular histochemical and ultrastructural features that most probably arise from the sarcoplasmic reticulum. Some studies have shown an additional mitochondrial origin of TAs. We studied the histopathological spectrum and clinical features in a large cohort of patients with TAs in their muscle biopsy (106 biopsies), derived from our muscle biopsy archive (15,412 biopsies in total). In particular, we examined light microscopic, enzyme histochemical, immunohistochemical and ultrastructural features in the muscle biopsies, as well as the patients' clinical data. We found TAs in 0.5% of all muscle biopsies. Based on the size of TAs, we identified two sub-groups: (1) myopathies with large TAs (29 biopsies) in type 2 fibers and sometimes also in type 1 fibers, absence of any other associated disorder, and a familial history in half of the cases, and (2) myopathies with small TAs (77 biopsies), exclusively in type 2 fibers, presence of another associated disease in the majority of patients and mostly no familial history. In the sub-group with large TAs, we observed a high variability of ultrastructural changes. The most frequent clinical symptom in both groups was limb muscle weakness. No significant differences in clinical presentation, age at onset or disease duration at the time of biopsy were found between the two groups. In conclusion, myopathies with TAs can be sub-divided into a group with large TAs, probably corresponding to the so-called primary TA myopathies, and into a group with small TAs as a feature of another underlying condition.