• Twelve patients suffering from congenital neuromuscular disorders showed at least two of the following structural changes in their muscle biopsy specimens: rods, cores, miniature cores (M lesions), and focal loss of cross-striations (F lesions).
There appeared to be no essential differences between M and F lesions except for the presence of vesicular nuclei in and around the latter.
A striking finding was the presence of adjacent M lesions, F lesions, or both in two or several adjoining muscle fibers. Serial sections often showed a definite relationship of the lesions with blood vessels. The finding of rods, cores, and M and F lesions, not only in one biopsy specimen but also in one muscle fiber, raised the intriguing possibility of common pathogenic mechanisms producing these lesions.
Bethlem J, Arts WF, Dingemans KP. Common Origin of Rods, Cores, Miniature Cores, and Focal Loss of Cross-Striations. Arch Neurol. 1978;35(9):555–566. doi:10.1001/archneur.1978.00500330003002