Anatomy

Neurons serve as the primary functional unit of the nervous system. The basis of the evaluation is centered around the basic components of a neuron. The components consist of a cell body that contains a nucleus and axon (nerve fiber) and creates an electrochemical action potential to stimulate communication with other neurons or muscle fibers; a dendrite that receives input from other neurons and transmits the signal to the cell body for interpretation; and the synapse, which is the connecting point between a neuron and muscle fiber or two neurons.

Peripheral nerves are a collection of thousands of nerve fibers whose cell bodies are located in either the dorsal root ganglia (sensory neurons) or the anterior horn (motor neurons) of the spinal cord. Nerve fibers can be characterized by the amount of myelin surrounding each axon. Myelin is an insulator that enhances the speed of action potential propagation. Thus, axons can be thinly myelinated (A-delta pain fibers), unmyelinated (temperature and pin prick), or thickly myelinated (motor or sensory fibers that carry vibration, light touch, and proprioception). Thin myelination is considered to be less than 0.5 mm, whereas thick myelination is greater than 1 mm.

Indications

Indications for NC-stat testing include the EMG diagnosis of the following:

Contraindications

Equipment and Supplies

NC-stat Biosensors

A biosensor is a preconfigured standard array of electrodes, eliminating the need for placement of multiple needles in very precise locations; multiple sites can be studied instead (Figs. 224-1 to 224-6). The NC-stat biosensor integrates flexible circuitry and a proprietary electrochemical gel with stimulus and sensing electrodes. An embedded chip monitors skin surface temperature, an important covariant for nerve conduction studies. A unique serial number is also embedded in the chip to conveniently link patients to their test results. Currently, biosensors are available for the median, ulnar, cubital, peroneal, sural, and tibial nerves.

Figure 224-1 A and B, Median nerve biosensor.

Figure 224-2 Ulnar nerve biosensor.

Figure 224-3 Cubital nerve biosensor.

Figure 224-4 Peroneal nerve biosensor.

Figure 224-5 Sural nerve biosensor.

Figure 224-6 Tibial nerve biosensor.

NC-stat Docking Station

This component receives nerve conduction data and waveforms from the monitor and, at the physician’s direction, can automatically transmit the data to the On-Call Information System at NeuroMetrix through any available analog telephone line (such as those used by facsimile machines) in minutes. The monitor can also be remotely upgraded by the docking station, thus ensuring that the system is always up to date with the latest software (Fig. 224-7).

Figure 224-7 The basic unit of operation in obtaining the recorded data.

Precautions

No general precautions are needed, except to remind the patient not to use lotions or oils, which may alter the quality of the signals evaluated. Alcohol wipes are sufficient to remove oils from contact points.

Preprocedure Patient Education and Forms

Patient education forms and insurance/Medicare/Medicaid waiver forms are available online at www.neurometrix.com.

Procedure

The bulk of this procedure is performed by ancillary staff. The biosensors are placed by staff who are trained in the proper technique or by the physician/clinician. Proper placement of the biosensors is essential for accurate interpretation of the submitted data (see Figs. 224-1 to 224-6). Instructions for the accurate placement of the leads and operation of the NC-stat module are found online at www.neurometrix.com. Proficiency in the use of the NC-stat system is easily attained. However, it is important to highlight the basic elements of interpretation of the traditional EMG, which correlate with the NC-stat system interpretation. The two major evaluative points of EMG or nerve conduction include (1) evaluation of spontaneous muscle activity performed while the muscle is at rest, and (2) evaluation of voluntary activity performed when the patient is requested to contract the muscle. The oscilloscope findings may demonstrate the muscle electrical potential tracings shown in Figures 224-8 to 224-10.

Figure 224-8 Normal wave pattern.

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