[Clinical and myopathological studies on rigid spine syndrome]

Rigid spine syndrome (RSS) is thought to be a group of heterogeneous muscle disorders. We reviewed the clinical and myopathologic findings of 55 patients with RSS including 49 previously reported and our own 6 patients. The results were as follows: the first, 80% showed restrictive ventilatory failure and 40% atrophy of the sternocleidomastoid muscle (SCM), which became manifest in the early stage of the illness, namely in less than 5 years from the onset. The second, paraspinal muscles usually began to be involved from the cervical semispinal muscle extending to other paraspinal muscles such as the more laterally located splenium muscle. The third, muscle biopsy demonstrated rimmed vacuoles (RV) in 41% of the 55 patients. RV were more frequently seen in the paraspinal muscles than the limb muscles, where marked myopathic changes of endomysial fibrosis and increased variation of the muscle fiber size were recognized. Based on the anatomical analysis of the paraspinal muscles, alligator sign, a radiological finding of the posterior opening between the cervical spine C1 and C2, seemed to result from the shortening of the cervical semispinal muscle due to its degeneration. This sign may, however, disappear as the whole paraspinal muscles including the semispinal muscles are affected. The RV seen in RSS seems to be a secondary, nonspecific structure related to the muscle degeneration. On the other hand, the above findings, namely the atrophy of SCM, restrictive ventilatory failure, and RV, have not been reported in Emery-Dreifuss muscular dystrophy (EDMD) so far. Accordingly, those findings and the absence of cardiac conduction abnormality are valuable for differential diagnosis of RSS from EDMD.