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Early ultrastructural alterations in adult dermatomyositis. Capillary abnormalities precede other structural changes
M De Visser1, A M Emslie-Smith, A G Engel
1Department of Neurology, University of Amsterdam, The Netherlands.
Abstract:
In 6 adults with dermatomyositis, minimally weak or nonweak muscles that showed inconclusive light-microscopic alterations were examined by electron microscopy. In all 6 specimens, this revealed pathologic changes in endomysial capillaries. The endothelial cells harbored microtubular inclusions and microvacuoles in all cases; pale swollen endothelial cells were observed in 3 specimens. There were no significant ultrastructural changes in the muscle fibers. In all cases, a small proportion of muscle capillaries were immunoreactive for complement membrane attack complex neoantigens. The findings imply that in adult dermatomyositis capillary injury precedes muscle fiber damage and infiltration by inflammatory cells, and that the microvasculature is an early and specific target of the disease process in muscle.
Insights
In adult dermatomyositis, electron microscopy reveals capillary damage precedes muscle fiber injury. This suggests the microvasculature is an early target in this inflammatory muscle disease.
Area of Science:
- Neurology
- Immunology
- Pathology
Background:
- Dermatomyositis is an idiopathic inflammatory myopathy.
- Muscle weakness is a primary symptom, but early pathological changes are not fully understood.
Purpose of the Study:
- To investigate ultrastructural changes in muscle capillaries in adult dermatomyositis.
- To determine if capillary pathology precedes muscle fiber damage.
Main Methods:
- Electron microscopy was used to examine muscle biopsies from 6 adults with dermatomyositis.
- Immunohistochemistry was performed to detect complement membrane attack complex neoantigens.
Main Results:
- Pathologic changes were observed in endomysial capillaries in all specimens.
- Endothelial cells showed microtubular inclusions and microvacuoles; some exhibited swelling.
- No significant ultrastructural changes were found in muscle fibers.
- Muscle capillaries were immunoreactive for complement membrane attack complex neoantigens.
Conclusions:
- Capillary injury is an early event in adult dermatomyositis.
- The microvasculature appears to be a specific early target in the muscle pathology of dermatomyositis.
- These findings suggest a potential mechanism for muscle damage in the disease.