Morphological and morphometrical study of human muscle spindles in Werdnig-Hoffmann disease (infantile spinal muscular atrophy type I).

A study was made of the morphological and morphometrical features of muscle spindles in biopsies of patients with Werdnig-Hoffmann disease (infantile spinal muscular atrophy type I) to investigate the possible involvement of the muscle spindles in the pathological processes of the disease. A total of 57 muscle spindles from 26 cases were studied. The parameters determined were: the diameter and area of spindles, the number, diameter and area of intrafusal fibers, the number and area of nuclei. In addition, the ratio of the area of the intrafusal fibers to the area of nuclei and the ratio of the area of the spindle to the area of the intrafusal fibers were calculated. Statistical evaluation of the data showed significant differences regarding the area of the muscle spindle, the diameter of the intrafusal fibers and the mean area of nuclei of the intrafusal fibers, which were all smaller in patients than in controls (p=0.03, 0.01 and 0.02, respectively), while the thickness of the capsule was greater in patients than in controls (p=0.01). Our results indicate that the muscle spindle participates in the pathological processes of Werdnig-Hoffmann disease.