Complex Repetitive Discharges

Sweep speed = 10 ms/div; Sensitivity = 0.1mV/div

Bursts of recurrently firing complex muscle action potentials Discharges of individual, and groups of, muscle fibers Origin: Muscle fibers Activated ephaptically: From muscle fiber to muscle fiber Time linked May be recurrent Persist with neurmuscular junction blockade Onset Stimulus: Spontaneous or with Muscle irritation Rate Range: 5 to 100 Hz Most common frequencies: 30 to 40 Hz More consistent during burst than myotonia Patterns Usual: Firing in a regular pattern Occasional: Abrupt change in frequency; Irregular firing Abrupt onset & end Non-rhythmic bursts Single fiber EMG: Low jitter Rarely or never the only abnormality on EMG Pathologic associations Chronic partial denervation: Grouped atrophy of muscle fibers, Large & Small Plexopathy or Radiculopathy Spinal muscular atrophy Motor neuron disease Not common in: Mononeuropathy; Acute disorders Myopathies Necrosis Inflammation Muscle fiber splitting Acid maltase deficiency May produce muscle hypertrophy Pharmacology: Corticosteroids may suppress CRDs