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Chapter 73: Electrodiagnostic Evaluation of Neuropathy

Leslie Zuniga; Mark A. Ross

INTRODUCTION

Electrodiagnostic studies are an important component of the evaluation of patients with suspected peripheral nerve disorders. The evaluation of the patient with suspected peripheral neuropathy involves consideration of multiple sources of information, including the clinical history, neurologic examination, electrodiagnostic (EDX) studies, and laboratory studies. Key questions such as the pattern of weakness and temporal history of sensory loss should be elicited during the history and physical examination (Table 73–1).1,3

Table 73–1Approach to Neuropathic Disorders: Seven Key Questions
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Table 73–1 Approach to Neuropathic Disorders: Seven Key Questions

  1. What systems are involved?

    Motor, sensory, autonomic, or combinations

  2. What is the distribution of weakness?

    Only distal vs. proximal and distal

    Focal/asymmetrical vs. symmetrical

  3. What is the nature of the sensory involvement?

    Temperature loss or burning or stabbing pain (e.g., small fiber)

    Vibratory or proprioceptive loss (e.g., large fiber)

  4. Is there evidence of upper motor neuron involvement?

    Without sensory loss

    With sensory loss

  5. What is the temporal evolution?

    Acute (days to 4 weeks)

    Subacute (4–8 weeks)

    Chronic (>8 weeks)

    Monophasic, progressive, or relapsing-remitting

  6. Is there evidence for a hereditary neuropathy?

    Family history of neuropathy

    Lack of sensory symptoms despite sensory signs

  7. Are there any associated medical conditions?

    Cancer, diabetes mellitus, connective tissue disease or other autoimmune diseases, infection (e.g., HIV, Lyme disease, leprosy)

    Medications including over-the-counter drugs that may cause a toxic neuropathy

    Preceding events, drugs, toxins

As an integral part of this comprehensive evaluation, electrodiagnostic studies can confirm and localize peripheral nerve disease, assess the type of nerve fiber involvement (motor and large sensory fibers), determine the distribution of nerve involvement, identify the underlying pathophysiologic process (axon loss, demyelination, or mixed features), determine the severity, and help monitor recovery or treatment effect (Fig. 73–1).

Figure 73–1

Approach to the evaluation of peripheral neuropathies. (CIDP = chronic inflammatory demyelinating polyradiculoneuropathy; EDx = electrodiagnostic; GBS = Guillain-Barré syndrome; IVIg = intravenous immunoglobulin) (Reproduced with permission from Amato AA, Barohn RJ. Peripheral Neuropathy. In: Kasper D, Fauci A, Hauser S, Longo D, Jameson J, Loscalzo J, eds. Harrison's Principles of Internal Medicine, 19e New York, NY: McGraw-Hill; 2014.)

"The sequence of evaluation is as follows. Does the patient complain of neuropathy? History and examination compatible with neuropathy? If No, evaluation of other disorder or reassurance and follow-up. If Yes, Mononeuropathy, Mononeuropathy multiplex, or Polyneuropathy. The evaluation for Mononeuropathy is as follows. E D x Is the lesion axonal or demyelinating? Is entrapment or compression present? Is a contributing systemic disorder present? Decision on need for surgery, nerve repair, transposition, or release procedure The evaluation for Mononeuropathy multiplex can be done in two ways. E Dx. Anoxal. Consider vasculitis or other multifocal process. Possible nerve biopsy. Treatment appropriate for specific diagnosis. E Dx. Demyelinating with focal conduction block. Consider multifocal form of CIDP. Test for paraprotein, HIV, Lyme disease. If tests are negative, consider treatment for CIDP. The evaluation for Polyneuropathy can be done in five ways. E Dx. Axonal. Subacute course, months. Review history for toxins, test for associated systemic disease or intoxication. Treatment appropriate for specific diagnosis. E Dx. Axonal. Chronic course, years. Review family history, examine family members, genetic testing. Genetic counseling if appropriate. E Dx. Demyelinating. Uniform slowing, chronic. Test for paraprotein, if negative. Review family history, examine family members, genetic testing. Genetic counseling if appropriate. E Dx. Demyelinating. Nonuniform slowing, conduction block. If chronic or subacute, C I D P. Treatment for C I D P. E Dx. Demyelinating. Nonuniform slowing, conduction block. If acute, G B S. I V Ig or plasmapheresis, supportive care including respiratory assistance."
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APPROACH TO THE EDX STUDY

The initial EDX studies in patients with suspected neuropathy should always include motor and sensory nerve conduction studies (NCSs) and needle electromyography (EMG) studies. The initial selection of nerves and muscles to study is guided by the clinical presentation of the individual patient. The NCSs are selected in the region of the patient's predominant clinical symptoms and pattern of involvement (Table 73–2).2

Table 73–2Patterns of Neuropathic Disorders
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Table 73–2 Patterns of Neuropathic Disorders
Pattern 1: Symmetrical proximal and distal weakness with sensory loss...

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