An augmented computer model of motor unit reorganization in neurogenic diseases of skeletal muscle.

A computer model of denervation and complete reinnervation in skeletal muscle was originally developed for the purpose of furthering an understanding of the underlying mechanisms of motor unit reorganization in neurogenic diseases. We now describe its successor, a computer model for investigating different rates of denervation and reinnervation, as well as incomplete reinnervation. The new model introduces the concept of permanent denervation and features enhanced interactive control over the distribution of motor unit centers and additional measures of dispersion and co-dispersion of muscle fibers. The use of this model for investigating pathophysiologically significant issues in denervating diseases is illustrated with five different sets of parameters. These simulate some of the processes that may be operational in chronic spinal muscular atrophy, amyotrophic lateral sclerosis, and progressive postpolio muscular dystrophy. The enhanced model will allow in-depth analysis of the influence of hypothesized pathophysiological processes on clinical, electrophysiological and pathological outcomes in human disease.

Quantitative morphometric study of muscle in inclusion body myositis.

Clinical and electromyographic findings do not clearly distinguish inclusion body myositis (IBM) from chronic polymyositis (PM). The rimmed vacuoles and filamentous nuclear and cytoplasmic inclusions that characterize IBM are often sparse and may be overlooked; conversely, these features may occasionally be seen in other diseases. Preliminary studies suggested that muscle fiber hypertrophy occurred more frequently in IBM than in PM. To investigate whether fiber hypertrophy can be used to improve the ability to separate IBM from PM, we report a morphometric analysis of 28 IBM cases, 22 PM and 22 dermatomyositis (DM) cases. The analysis, using a computer automated system, included proportion of hypertrophied fibers and also fiber type proportions, average fiber diameter, proportion of atrophic and angulated fibers, and the co-dispersion index (CDI). The proportion of hypertrophied fibers was greater in IBM than the other two conditions (IBM (mean +/- SEM) 31.0 +/- 4.7% and 12.2 +/- 2.4% for type 1 and type 2 fibers, respectively, compared to 9.8 +/- 3.0% and 3.3 +/- 1.7% in PM, and 7.7 +/- 2.7% and 3.9 +/- 1.9% in DM). These differences were statistically significant (P < 0.05) in both sexes for type 1 fibers and in women for type 2 fibers. Also, the average fiber size and hypertrophy factors for type 1 and type 2 fibers were increased in IBM compared to PM and DM. This study confirms that the presence of muscle fiber hypertrophy in biopsies from IBM patients may help differentiate them from other clinically similar inflammatory myopathies.