Muscle pathology in ankylosing spondylitis.

The results of histological, histochemical and electron microscopic study of the muscular involvement in eight patients with Ankylosing Spondylitis (AS) are described. Muscle tissue from all these patients showed gross abnormalities of the sacrospinalis muscle, which had a 'targetoid core' appearance common to several myopathic and neurological diseases. In our opinion, there is always constant and early involvement of this muscle in AS. Several factors associated with the disease (chronic inflammation, multiple enthesopathies, muscle stiffness and bone lesions) could be responsible for this not fully understood aspect of AS. They may lead to a non specific damage of the nervous and/or muscular components of the spine in these patients.