GENERAL INDICATIONS FOR MUSCLE BIOPSIES

• Presence of some evidence of muscle disease
  • Weakness
  • Muscle symptoms: Discomfort; Cramps; Fatigue with activity (r/o myasthenia)
  • Elevated (very high or high) creatine kinase (CK)
  • Myopathic EMG
• Presence of a neuropathy for which a nerve biopsy is indicated
• Presence of a systemic disorder that may have silent manifestations in muscle
  • Vasculitis
  • Sarcoidosis
• Not generally indicated in some disorders better diagnosed by electrodiagnostic methods
  • Myasthenia gravis (May be suggested on biopsy if esterase-stained NMJs are small)
  • Myotonias

SELECTION OF MUSCLE TO BIOPSY

• Chronic disease: Muscle with moderate, but not severe, weakness
• Acute disease: Muscle with severe or moderate weakness
• Best specific muscles: Deltoid; Biceps; Quadriceps
• MRI can be used to select pathological muscle site in difficult cases
• Avoid: Muscles that were site of EMG, injections,or trauma

BIOPSY PROCEDURES

• Technique: We almost always use open biopsy procedure to obtain muscle.
  • Open biopsy strongly indicated for disorders with patchy pathology, e.g. polymyositis
  • Do not use cautery, sutures, or clamps.
  • Some laboratories use needle for many biopsies to minimize trauma.
    • May miss patchy or epimysial pathology
  • Obtain several samples from biopsy site: Especially with possible
    • Multifocal disease: Inflammatory myopathies
    • Need for metabolic analysis
• Transportation
  • Muscle may be saved in saline moistened gauze for several hours.
  • Keep specimen cool.
  • Muscle should NOT be immersed in saline, fixative or other liquids.
  • Frozen muscle may be safely shipped "overnight" with adequate dry ice
• Preservation
  • Freeze most tissue in isopentane precooled to -160^oC in liquid nitrogen.
    • Frozen muscle for histochemistry provides
      • Excellent muscle fiber morphology
      • Most diagnostic information with light microscopy
    • Freezing process should be rapid to prevent artifact.
    • Store frozen muscle at -80^oC.
  • Fix some muscle in 4% glutaraldehyde.
    • Embed most fixed muscle in plastic
      • For ultrastructural analysis, if necessary
      • Good visualization of muscle endomysial capillaries
    • Paraffin embedded material
      • Useful for surveys for inflammation & morphology of inflammatory cells
      • Gives poor muscle fiber morphology