To Determine Diagnosis

A nerve disorder can be from the brain, anterior horn cell, spinal root, plexus, peripheral nerve(s), neuromuscular junction, and/or the muscle. 

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Deciphering between central versus peripheral nervous system lesions

• Neurological symptoms resulting from stroke, brain injury, spinal cord injury, multiple sclerosis, and other central processes appear normal on electrodiagnostics

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Motor neuron disease

• Neurological symptoms arising from disease of the anterior horn cells appear abnormal on electrodiagnostics
• Presently, we do not manage motor neuron disease. If this is highly suspected, we refer to the appropriate neuromuscular experts

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Root avulsion

• Patients typically complain of very severe pain with true root avulsions. This can be seen with the presence of a pseudomeningocele on MRI of the cervical spine
• Electrodiagnostics can assess the completeness of the root avulsion, if present

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Radiculopathy

• Electrodiagnostics rarely produce false positive results, whereas imaging studies are notorious for demonstrating incidental abnormalities   
• Electrodiagnostics help determine the severity of a radiculopathy by quantifying axonal damage, if present
• In this way, electrodiagnostics aligns the patient history, physical examination, and imaging to help determine whether the apparent pathology is of clinical significance
• Reasons why nerve conduction studies may be “normal”
  • Most radiculopathies are sensory in nature, and with pathology being proximal to the dorsal root ganglion (DRG), nerve conduction studies appear normal as Wallerian degeneration proceeds centrally
  • An exception to this rule is an L5 radiculopathy, where the DRG is within the intervertebral foramen, but this is rare
• Reasons why needle EMG studies of the muscle may be “normal”
  • The injury is affecting purely sensory nerves, and so the axons of motor neurons are intact
  • The injury is purely demyelinating, and so the signaling of motor neurons is intact. A complete conduction block, however, would demonstrate reduced recruitment of motor units
  • The injury is acute, and so a pattern of muscle involvement proximal to distal cannot be demonstrated
  • The section of muscle sampled may be spared given input from other roots
  • The entire muscle is spared as the nerve fascicle supplying it is unaffected at the root-level  

Plexopathy (cervical/lumbosacral)

• Electrodiagnostics can help identify specific nerves involved and non-compressive lesions where imaging may be normal
• Plexopathies can occur for many reasons, from acute trauma, compression, even systemic disease (e.g. diabetes, autoimmune)
• Presently, we do not assess plexopathies in babies as a result of birth trauma

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Peripheral nerve

• Common examples include
  • Median nerve at the wrist (carpal tunnel syndrome)
  • Ulnar nerve at the elbow
  • Sciatic nerve near the low back (“sciatica”)
  • Fibular nerve at the knee (“drop foot”)

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Polyneuropathy (PN)

• Common causes include diabetes, medications, and nutritional deficiencies
• Electrodiagnostics helps categorize PN into primarily demyelinating, mixed, or axonal categories. It can further separate it into uniform, segmental, or length-dependent processes. This may affect only sensory, only motor, or both types of nerves. Standard electrodiagnostics cannot detect a predominately small fibre process.
• Presently, we do not offer nerve biopsies for small fibre testing, but this is often not required for diagnosis. 

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Neuromuscular junction

• Diseases of the neuromuscular junction include myasthenia gravis and Lambert-Eaton myasthenic syndrome
• Presently, we do not offer repetitive nerve conduction testing or single fibre EMG. If this is highly suspected, we refer to the appropriate neuromuscular experts

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Myopathy

• Needle EMG can identify muscle membrane irritability and disrupted motor units
• Presently, we do not offer perform muscle biopsies. If this is highly suspected, we refer to the appropriate neuromuscular experts