Complex Repetitive Discharges (CRDs)

Sweep speed = 10 ms/div; Sensitivity = 0.1mV/div
Complex muscle action potentials: Bursts; Recurrently firing
Complex Repetitive Discharges (CRDs)
  • General description
    • Complex of muscle fiber action potentials
    • Firing pattern: Repeated, Regular
    • Onset or Cessation: Abrupt
  • Features: Discharges of individual, and groups of, muscle fibers
    • Origin: Muscle fibers
      • Groups (Neighboring fibers)
      • Membranes have lower threshold for generating recurring action potentials
      • Activated ephaptically: From muscle fiber to muscle fiber
    • Other properties
      • Time linked
      • May be recurrent
      • Persist with neurmuscular junction blockade
    • Onset
      • Stimulus: Spontaneous or with Muscle irritation
    • Firing Rate
      • Range: 5 to 150 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
      • Associations
        • Usual: Occur in presence of other EMG abnormalities
        • Few patients: Only abnormality on EMG 1
          • Muscle involvement
            • Legs: Tensor fasciae latae, Gluteus maximus
            • Arms: Biceps brachii, Pronator teres
          • Associated lesions: L5; C6
          • Clinical syndrome: Pain, radicular or limb
  • Pathologic associations
  • Pharmacology: Corticosteroids may suppress CRDs
from M. Al-Lozi

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1. Muscle Nerve 2022 Nov 23