MYOPATHIES WITH MYOSIN LOSS

Myosin Loss: Histochemistry H&E stain Some patients have small angular fibers on H&E stain. These small fibers often are basophilic and have large nuclei (Right).

Gomori trichrome stain	NADH stain
The small muscle fibers stain darkly on Gomori trichrome & NADH.

ATPase pH 9.4 stain
The small muscle fibers with myosin loss have less staining than type I muscle fibers on ATPase pH 9.4 stain.

Comparison of ATPase pH 9.4 (Left) & 4.3 (Right) in serial sections
Type I fibers (1): Darker staining at pH 9.4 than 4.3 Type II fibers (2): Darker staining at pH 4.3 than 9.4 Myosin loss fibers (0 or arrows): No staining at both pH 9.4 and pH 4.3
ATPase pH 9.4 stain	ATPase pH 4.3 stain

Myosin Loss: Anti-myosin antibody Reduced myosin in many small   muscle fibers

H & E stain		Myosin ATPase, pH 9.4 stain
A focal pattern of myosin loss may also occur in muscle fibers.   Focal regions of myosin loss in type I and II muscle fibers.   These regions appear basophilic on H & E stain.   Myosin loss may occur in large as well as small fibers

Myosin loss: Ultrastructure Thick filament loss with relative preservation of thin filaments & Z-lines From: R Schmidt Thick filament loss can involve some regions within muscle fibers but not others