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
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What systems are involved?
Motor, sensory, autonomic, or combinations
What is the distribution of weakness?
Only distal vs. proximal and distal
Focal/asymmetrical vs. symmetrical
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)
Is there evidence of upper motor neuron involvement?
Without sensory loss
With sensory loss
What is the temporal evolution?
Acute (days to 4 weeks)
Subacute (4–8 weeks)
Chronic (>8 weeks)
Monophasic, progressive, or relapsing-remitting
Is there evidence for a hereditary neuropathy?
Family history of neuropathy
Lack of sensory symptoms despite sensory signs
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).
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.)
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