Latent trigger points: Biopsies of latent trigger points stained appropriately showed accumulation of fine fat droplets in the muscle cells.

Active trigger points: Biopsies showed fat dusting and mild dystrophic changes.  The muscle fibers were variable in width, and stain uptake, and contained increased numbers of nuclei inside and outside the muscle fibers.

Vigorously Active trigger points: More severe dystrophic pathology has been demonstrated by electron microscope:

• Interstitial abnormalities with or without fiber degeneration,
• Contracture knots, club-like distensions of contracted myofibrils beside a section of empty sarcolemma tube
• Loss of cross striations
• Extreme variability in staining of fibers
• Dense accumulation of nuclei, especially near blood vessels
• Fat and connective tissue replace muscle fibers
• Intracellular lipid droplets
• Interstitial infiltration with mucopolysaccharide deposits in 75% of "fibrositis" muscles as compared with 25% of controls
• Degranulating mast cells
• Platelets occurring in large clusters
• Giant sarcomeres extending beyond z-lines

Four Stages in the degenerative Process:

1. Mitochondria are swollen.  Myofilaments are moth-eaten in the I-band where actin attaches to the Z line, which marks the end of the sarcomere.
2. Myofilament destruction included A bands (myosin). Z bands are intact.
3. Disrupted sarcomere remnants are scattered but recognizable.
4. Complete destruction of contractile substance with fine granular residue within the sarcolemma. Accumulations of collagen appear in the area of necrosis.