Severely atrophic muscle fibers with nuclear clumps survive many years in permanently denervated human muscle.

The Open Pathology Journal 2009; 3: 106-110. Severely atrophic muscle fibers with nuclear clumps survive many years in permanently denervated human muscle Helmut Kern, MD,1 Ugo Carraro, MD,2 Donatella Biral, DBiol,3 Nicoletta Adami, DBiol,2 and Sandra Zampieri, DBiol, PhD4 1 Ludwig Boltzmann Institute of Electrostimulation and Physical Rehabilitation, Department of Physical Medicine, Wilhelminenspital. A-1171 Vienna, Austria. 2 Laboratory of Translational Myology of the Interdepartmental Research Center of Myology, c/o Department of Biomedical Science, University of Padova, I-35121 Padova, Italy. 3 C.N.R. Institute of Neuroscience c/o Department of Biomedical Science, University of Padova, I-35121 Padova, Italy. 4 Division of Rheumatology, Department of Clinical and Experimental Medicine, University of Padova, Italy Abstract After complete lumbar-ischiatic spinal cord injury (SCI) the lower motor neuron (LMN) denervated human muscle fibers lose completely the myofibrillar apparatus and the coil distribution of myonuclei that are relocated in groups (nuclear clumps) in the center of these “severely atrophic” muscle fibers. In our cohort of patients, the “severely atrophic” myofibers are frequent in muscle biopsies harvested three to six years after SCI. Up to two years of LMN denervation the muscle fibers with nuclear clumps are 2±5 % (mean ±SD) of the total muscle fibers. The percentage increases to 27±9 % between three and six years of denervation (p< 0.001), and then abruptly decrease from the 6th year of LMN denervation onward, when fibrosis takes over to neurogenic muscle atrophy. Immunohistochemical analyses show that nuclear grouping occurs in both fast and slow muscle fibers. These results show that human muscle fibers survive permanent denervation much longer than generally accepted.