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
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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
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Neurological symptoms arising from disease of the anterior horn cells appear abnormal on electrodiagnostics
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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
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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
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Electrodiagnostics can assess the completeness of the root avulsion, if present
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Radiculopathy
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Electrodiagnostics rarely produce false positive results, whereas imaging studies are notorious for demonstrating incidental abnormalities
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Electrodiagnostics help determine the severity of a radiculopathy by quantifying axonal damage, if present
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In this way, electrodiagnostics aligns the patient history, physical examination, and imaging to help determine whether the apparent pathology is of clinical significance
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Reasons why nerve conduction studies may be "normal"
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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
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An exception to this rule is an L5 radiculopathy, where the DRG is within the intervertebral foramen, but this is rare
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Reasons why needle EMG studies of the muscle may be "normal"
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The injury is affecting purely sensory nerves, and so the axons of motor neurons are intact
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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
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The injury is acute, and so a pattern of muscle involvement proximal to distal cannot be demonstrated
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The section of muscle sampled may be spared given input from other roots
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The entire muscle is spared as the nerve fascicle supplying it is unaffected at the root-level
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Plexopathy (cervical/lumbosacral)
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Electrodiagnostics can help identify specific nerves involved and non-compressive lesions where imaging may be normal
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Plexopathies can occur for many reasons, from acute trauma, compression, even systemic disease (e.g. diabetes, autoimmune)
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Presently, we do not assess plexopathies in babies as a result of birth trauma
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Peripheral nerve
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Common examples include
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Median nerve at the wrist (carpal tunnel syndrome)
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Ulnar nerve at the elbow
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Sciatic nerve near the low back (“sciatica”)
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Fibular nerve at the knee (“drop foot”)
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Polyneuropathy (PN)
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Common causes include diabetes, medications, and nutritional deficiencies
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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.
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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
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Diseases of the neuromuscular junction include myasthenia gravis and Lambert-Eaton myasthenic syndrome
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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
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Needle EMG can identify muscle membrane irritability and disrupted motor units
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Presently, we do not offer perform muscle biopsies. If this is highly suspected, we refer to the appropriate neuromuscular experts