Nerve conduction study

Nerve conduction studies (NCS) evaluate the function of individual nerves. During NCS, the nerve of interest is stimulated (electrical pulse) at one location while electrodes (wires taped to the skin) record from a different site along the same nerve. The NCS is performed to measure the timing (latency, conduction velocity), size (amplitude), and shape (morphology) of the nerve's response to the stimulus across any given segment of its pathway. NCS can be performed on strictly motor or sensory fibers, or a nerve containing both motor and sensory fibers (a mixed nerve).

Other types of NCS include:

Inching

Inching, or Short-Segmental Incremental Stimulation (SSIS), is a technique that tests a region of suspected focal slowing, or conduction block. The nerve is stimulated above and below the presumed site of the block at 1-cm intervals, while searching for a dramatic focal change in latency.

Repetitive Stimulation

This is the procedure of evaluating the neuromuscular junction (NMJ) by recording muscle responses to a series of stimuli both before and after exercise, or following a train of high-frequency stimuli.

Blink Reflex

A blink reflex is the electrophysiological analog of the corneal reflex. The test can detect early pathologies of the fifth (trigeminal) and/or seventh (facial) cranial nerves, or cerebellopontine angle tumors.

Jaw Jerk Reflex

The Jaw Jerk Reflex is the stimulation and recording of the monosynaptic volley from the jaw (mandible) to the brainstem (trigeminal motor nucleus).

Masseter Inhibitory Reflex

A Masseter Inhibitory Reflex (MIR) consists of recording the marked attenuation of muscle-activity that is elicited by stimulation of the mental nerve during maximum contraction of a jaw (masseter) muscle.

H-Reflex

The H-Reflex is the electrophysiological correlate of the monosynaptic ankle tendon reflex that volleys through the spinal cord. The exam helps evaluate proximal peripheral nerve segments that are inaccessible by routine NCS. It also can be used to assess motor neuron excitability.

Electromyography

Electromyography (EMG) is a procedure which examines the spontaneous and volitional electrical activity of muscle, or motor unit potentials (MUPs), using a disposable needle electrode.

Specializations of EMG include:

Quantitative EMG

Quantitative EMG (QEMG) is the process of collecting, recording and analyzing (duration, amplitude, turns, proportion of polyphasics) a representative sample of MUPs from a given muscle.

Single Fiber EMG

Single Fiber EMG (SFEMG) is a specialized type of EMG that assesses the integrity of the NMJ. The exam requires the use of a unique needle electrode which records the time-variability (or "jitter") between the activation of a motor nerve and the generation of its individual muscle fiber action potentials.

Autonomic Nervous System Evaluation

Quantitative Sensory Testing

Quantitative Sensory Testing (QST) examines the function of small-diameter peripheral nerves that are responsible for the sensation of temperature and vibration. After various cold/warm/vibration stimuli are presented to either the hand or foot, stimulus thresholds are calculated. These techniques help assess altered sensory functions that contribute to neuropathic pain.