Abstract
It is believed that one muscle fiber consists of one fiber type determined by its innervating neuron. In biopsied muscles of Duchenne muscular dystrophy (DMD), however, the author has incidentally found a double-typed fiber which is divided into inner and outer parts. The author termed it a “boiled-egg fiber”. The author has examined the appearance rate of the boiled-egg fibers on 682 biopsied muscles obtained from patients with various neuromuscular disorders, and classified the types of the inner and outer parts of the boiled-egg fibers by ATPase staining.
Boiled-egg fibers were recognized in 17 cases out of 60 with DMD, 5 out of 146 with other types of muscular dystrophy and 6 out of 94 with myositis. No boiled-egg fiber was found in the remaining 382 cases with other disorders which did not represent necrosis with regeneration of muscle fibers. The total number of boiled-egg fibers was 235 with 192 in DMD and 43 in other disorders. 197 of 235 (83.8%) had the same type for both inner and outer parts and remaining 38 (16.2%) had different types for their inner parts. In 133 of 235 (56.6%), the inner parts were type 2C fibers. Boiled-egg fibers were segmentally found with the length of several hundred micrometers.The above findings suggest that boiled-egg fibers reflect an abnormal regenerating process. It remains to be clarified whether or not inner and outer parts of boiled-egg fibers are double-innervated respectively.
