The histographic analysis of human muscle biopsies with regard to fiber types

Histograms were constructed of each biopsy, using the techniques previously described.’ The only modification was that the magnification used for taking the photographs from which histograms were made was altered in some cases. Magnifications of 2 0 0 ~ and 4 0 0 ~ were used when the standard 100 x -magnification was insufficient to produce a photograph containing about 200 fibers in an area of about 12 sq. in. Histograms were plotted independently for each of the two main fiber types. There was only one criterion for including a patient in the study and that was that the patient was 15 years of age or less. There were many different disease categories and many patients with diseases that did not fall into a clear-cut diagnostic category. Thus, to present the results by classifying the patients under disease categories would be a confusing and cumbersome approach. All of the 180 biopsies fell into one of five clear-cut histographic types. The patients are therefore presented according to the histographic appearance of their biopsies. These groups are de6ned more exactly below, but they may be summarized as [ l ] biopsies with fiber types I and I1 of equal size and apparently normal variability, 121 biopsies with type I1 fibers smaller than type I, [3] biopsies with type I fibers smaller than type 11, 141 biopsies with a twin-peaked histogram of one or both fiber types, and [5] biopsies with an abnormal variability in the size of individual fibers not fitting into one of the other groups.