Electrodiagnostic studies

Electrodiagnostic studies

• Creating a standard calibration curve

• Accuracy within 5%–10%

• Radiation dose higher than that for DEXA

   

• Most accurate and reliable for predicting fracture risk

• Radiation dose lower than that for quantitative CT

• Measures bone mineral content and soft tissue components

  • Nerve conduction studies

    • Evaluation of peripheral nerves

    • Nerve impulses stimulated and recorded by surface electrodes

      • Allows calculation of conduction velocity

    • Measures latency (time from stimulus onset to response) and response amplitude

    • Late responses (F wave, H reflex) allow evaluation of proximal lesions.

      • Impulse travels to the spinal cord and returns

  • Electromyography

     

    Table 1.42

     

    Nerve Conduction Study Results

     

     

    Condition Latency Conduction Velocity Evoked Response
    Normal study	Normal	Upper extremities: >45   m/sec; lower extremities: >40 m/sec	Biphasic
    Axonal neuropathy	Increased	Normal or slightly decreased	Prolonged, decreased amplitude
    Demyelinating neuropathy	Normal	Decreased (10%–50%)	Normal or prolonged, with decreased amplitude
    Anterior horn cell disease	Normal	Normal (rarely decreased)	Normal or polyphasic, with prolonged duration and decreased amplitude
    Myopathy	Normal	Normal	Decreased amplitude; may be normal
    Neurapraxia:
    Proximal to   lesion	Absent	Absent	Absent
    Distal to lesion	Normal	Normal	Normal
    Axonotmesis:
    Proximal to   lesion	Absent	Absent	Absent
    Distal to lesion	Absent	Absent	Normal
    Neurotmesis:
    Proximal to   lesion	Absent	Absent	Absent
    Distal to lesion	Absent	Absent	Absent

     

     

    Modified from Jahss MH: Disorders of the foot, Philadelphia, 1982, Saunders.

     

    • Use of intramuscular needle electrodes to evaluate muscle

      units

    • Used to evaluate denervation

      • Fibrillations; earliest sign usually at 4 weeks

      • Sharp waves

      • Abnormal recruitment pattern

    • Interpretation

      • Peripheral nerve entrapment syndromes

      • Distal motor and sensory latencies more than 35 m/sec

      • Nerve conduction velocities less than 50 m/sec

      • Changes over a distinct interval (Table 1.42)