From the Guidelines
Nerve conduction studies (NCS) should be interpreted in the context of the patient's clinical presentation, taking into account the amplitude, latency, conduction velocity, and waveform morphology of the recorded responses, as well as patient factors like age, height, and temperature, to accurately diagnose neurological disorders. When interpreting NCS, it is essential to consider the parameters that reflect the health and function of peripheral nerves, including amplitude, latency, conduction velocity, and waveform morphology 1. The amplitude measures the strength of the nerve signal and correlates with the number of functioning nerve fibers, while reduced amplitude suggests axonal loss or conduction block. Latency refers to the time taken for the impulse to travel from stimulation to recording site, with prolonged latencies indicating demyelination. Conduction velocity calculates how fast signals travel along the nerve, with slowed velocities typically indicating demyelinating processes.
Key Parameters for Interpretation
- Amplitude: measures the strength of the nerve signal and correlates with the number of functioning nerve fibers
- Latency: refers to the time taken for the impulse to travel from stimulation to recording site
- Conduction velocity: calculates how fast signals travel along the nerve
- Waveform morphology: examines the shape and characteristics of the recorded responses
Clinical Context
The diagnosis of painful diabetic peripheral neuropathy (DPN), for example, relies on the patient's description of pain, symptoms, and clinical examination, with NCS and quantitative sensory testing providing supporting evidence 1. The clinical diagnosis may be supported by NCS, which are particularly important to exclude other cases of pain, such as entrapment syndromes. The pattern of abnormalities in NCS helps distinguish between axonal neuropathies, demyelinating conditions, focal nerve injuries, and more diffuse processes.
Limitations and Considerations
It is crucial to consider technical factors and anatomical variations that can influence NCS results, as well as the patient's clinical presentation, to accurately interpret the findings. Additionally, NCS may not detect small fiber neuropathy, which constitutes a significant proportion of peripheral nerve fibers and underlies the symptoms of painful diabetic neuropathy 1. Therefore, a validated measure of small fiber neuropathy may be used to define and quantify the severity of diabetic sensori-motor polyneuropathy, especially when NCS are normal.
From the Research
Interpretation of Nerve Conduction Studies
Nerve conduction studies (NCS) are a crucial diagnostic tool for evaluating neurological disorders, particularly those affecting the peripheral nervous system. The interpretation of NCS involves analyzing the results to determine the presence, location, and severity of nerve damage or dysfunction.
Key Components of NCS Interpretation
- Nerve conduction velocity: reflects the speed of propagation of action potentials along large myelinated axons in a peripheral nerve 2
- Amplitude of sensory nerve action potentials (SNAPs): determined by the number of axons in a sensory nerve 2
- Amplitude of compound motor action potentials (cMAPs): reflects integrated function of motor axons, neuromuscular junction, and striated muscle 2
- Pattern of abnormalities: distinguishes between primarily axonal and demyelinating pathology, and helps to identify the severity of neuropathic damage 3
Patterns of Abnormality
- Demyelinating neuropathies: characterized by slowing of nerve conduction, increased temporal dispersion, or conduction block 3
- Axonal neuropathies: mainly affect sensory nerve and compound muscle action potential amplitudes 3
- Hereditary vs. acquired demyelinating neuropathies: distinguished by the pattern of demyelination, with hereditary neuropathies typically showing uniform demyelination and acquired neuropathies showing segmental demyelination 3
Clinical Applications
- Diagnosis of peripheral neuropathies: NCS helps to diagnose and classify neuropathies, and to distinguish between different types of neuropathies 3, 2
- Identification of nerve damage: NCS can detect damage to motor and/or sensory nerve cell bodies or peripheral nerves, and indicate the primary target of the damage (axon or myelin sheath) 2
- Localization of nerve damage: NCS can determine the distribution of nerve damage, whether it is generalized, multifocal, or focal 2