A H & E stain Image: Small angular muscle fibers |
What are causes of small angular muscle fibers? Answers Subacute partial denervation Type 2 muscle fiber atrophy Myosin-loss (Critical illness) myopathy Inclusion body myopathies What stains are useful in this differential diagnosis? Answers ATPase Denervation: Small fibers of both types Type 2 atrophy: Smallest fibers are type 2 Myosin loss: ATPase pH 9.4 shows muscle fibers with staining intensity less than type 1 H&E: Small angular fibers have large nuclei Non-specific esterase & NADH stain of small fibers: Denervation dark; Type 2 atrophy pale |
B ATPase pH 9.4 stain |
What disease most commonly produces this pattern of muscle fiber types & size changes? Image: Region of grouped atrophy with muscle fibers of mixed types Answer: Amyotrophic lateral sclerosis Multiple small regions of grouped atrophy Fibers in area of grouped atrophy commonly have varied types. |
C NADH-TR stain |
What processes produce this anatomical change in muscle fibers? What muscle most frequently shows this change? Could these be cores? Image: Rounded clear regions with dark rim & internal regions of staining Answers: Targets Most sensitive stains: NADH; COX; SDH; Caveolin-3 Occur with: Subacute denervation, possibly with some reinnervation; Tenotomy Especially common in the gastrocnemius muscle Often have darker rims and central staining regions, but cores do not |
D ATPase pH 9.4 stain |
What disease processs most commonly produces this pattern of muscle fiber types & size changes? Image Large grouped atrophy Large muscle fibers: Predominantly type 1 Small fibers: Mixed type Answers: Spinal muscular atrophy Small fibers in SMA may be mostly type 2 or of mixed type Other causes of chronic partial denervationgwith reinnervation may also produce this pattern |
E VvG stain |
What is this structure (arrow)? What stains best visualize it? Answer: Polyglucosan body Polyglucosan bodies in terminal axons in muscle are non-specific. They are most easily seen on VvG stain. The swellings are positively staind by PAS. Diseases that cause polyglucosan bodies and other axonal swellings |
F H & E stain |
What is this dark stained structure (arrow)? Answer: Pyknotic nuclear clump How did it develop? Answer: A muscle fiber that is so severely atrophied that only its pyknotic (dark shrunken) nuclei remain. What disorders can produce it? Answers Chronic denervation of a muscle fiber without reinnervation Neuropathies, chronic Myasthenia gravis: Under-treated Myotonic dystrophy General: Pyknotic nuclear clumps suggest a neuropathy but are not specific for denervation. |