Internally nucleated skeletal muscle fibers

What it means

An abnormally increased proportion of nuclei of sarcomeres with an internal localization. Individual muscle fibers are syncytia, formed by embryonic fusion of many myoblasts or later, myosatellite cells. Each muscle fiber contains many nuclei, peripherally positioned immediately adjacent to the sarcolemmal membrane. In healthy muscle only 3-5% of fibers contain nuclei that are located internally, within the cell, but many disease processes lead to internal nuclei.

A normal muscle fiber contains many nuclei, peripherally positioned immediately adjacent to the sarcolemmal membrane. In healthy muscle only 3-5 percent of fibers contain nuclei that are located internally, within the cell, but many disease processes lead to internal nuclei.

Rare diseases that can present with this5

The range is how often this sign appears among people diagnosed with each disease — it is not a probability of having any of them. Many of these signs also occur in common, non-rare conditions. A sign on this page is a conversation to have with a clinician, not a conclusion.

Part of the broader category

Also called: Internally nucleated skeletal muscle fibres