Article Text
Abstract
Objective: To characterise morphological abnormalities in relation to muscle fibre type in sporadic inclusion body myositis (s-IBM).
Methods: 14 muscle biopsies from 11 patients with s-IBM were characterised for morphological abnormalities and fibre type composition as well as muscle fibre regeneration and cytoskeletal structure, using histochemical and immunohistochemical techniques.
Results: Morphological abnormalities included inflammatory infiltrates and “rimmed vacuoles,” and pronounced variation in fibre size. There were no significant differences in fibre type composition between s-IBM patients and controls based on the myofibrillar ATPase staining. A differential effect on muscle fibre sizes was noted, type II fibres being smaller in the s-IBM patients than in the controls. Conversely, the mean type I muscle fibre diameter in the s-IBM patients was larger than in the controls, though this difference was not significant. An ongoing intense regeneration process was present in s-IBM muscle, as indicated by the expression of neonatal myosin heavy chain, vimentin, and CD56 (Leu-19) in most of the muscle fibres. The cytoskeletal proteins dystrophin and desmin were normally expressed in s-IBM muscle fibres that were not undergoing degeneration or regeneration.
Conclusions: There are extensive morphological and morphometric alterations in s-IBM, affecting different muscle fibre types in different ways. The cytoskeletal structure of type I and II muscle fibres remains unaffected in different stages of the disease.
- inclusion body myositis
- cytoskeletal structure
- muscle fibre regeneration
- myosin heavy chain
- CMT, Charcot-Marie-Tooth disease
- CP, cricopharyngeus muscle
- mATPase, myofibrillar ATPase
- MCSA, mean cross sectional area
- MHCf, fast myosin
- MHCn, neonatal myosin
- MHCs, slow myosin
- s-IBM, sporadic inclusion body myositis
- TA, tibialis anterior muscle
- VA, vastus lateralis muscle
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Footnotes
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Competing interests: none declared