A complete and thorough neurological examination is of extreme importance in patients suffering from lower extremity nerve disorders. The Podiatrist must be able to monitor the course of the neuropathy and stratify patients according to their risk factors. Those patients found to be at high risk can be treated prophylactically with accommodative orthoses, custom molded shoes, braces and/or surgery. Traditional methods of assessing the sensory nervous system includes semm weinstein filaments, tuning fork and use of a pinwheel are highly subjective, variable and prone to the examiner bias, making their use for assessment over time very difficult. Current Perception Threshold evaluations that can be performed in the office and aid in the diagnosis and treatment of neuropathy and nerve entrapment/compression syndromes.
The current perception threshold evaluation is a quantitative test which provides a reproducible functional assessment of the peripheral sensory nervous system.1 The current perception threshold is the minimum amount of a transcutaneously applied current that an individual consistently perceives as evoking a sensation. The evaluation is painless, non-invasive and easy to perform. The current perception threshold evaluation is performed using the Neurometer CPT/C Device. This is a neuroselective diagnostic stimulator which uses a microprocessor-controlled stimulus to obtain current perception threshold measures. The electrical stimulus selectively excites distinct subpopulations of nerve fibers as a function of the sinusoid frequency.2 The 2000-Hz stimulus evokes responses from the A beta, the 250-Hz stimulus evokes responses from the A delta, and the 5-Hz evokes responses from the C fibers. As compared to Nerve Conduction Velocity, tests solely large fiber function and thermal perception threshold, test solely small fiber function. These different nerve-fiber populations have shown varying susceptibilities in radiculopathies and compressive neuropathies.3 Patients with neuropathy have been shown to anesthetic to the maximum stimulus at one frequency of the current perception threshold evaluation but within normal threshold range for the other 2 frequencies.4 Therefore, the testing of all three nerve fibers is of the utmost importance.
The procedure for CPT evaluations is quite simple. The patient is made comfortable in a location with minimal distractions. A pair of 1 cm diameter electrodes is coated with conductive gel and then taped to the body site that is being tested. The device controls are shielded from the patient's view and the sinusoidal electrical stimulus is slowly increased, from 0.00 up to 9.99mA, until the patient reports feeling it. The stimulus is then turned off, the intensity level lowered, change the frequency level and then the stimulus is turned back on.
The Neurometer CPT devices are prescription devices and U.S. Federal Law requires that they be limited to use only by or under the order of a physician or other appropriate medical personnel. The Neurometer was approved by the F. D. A. in 1986.
Quantitative sensory nerve testing with the current perception threshold evaluation provides an objective, reproducible, reliable and painless measure of both Hyperesthesia and Hypoesthesia in the 3 different nerve fibers; A beta, A delta and C fibers. This is extremely helpful in the initial evaluation and workup of patients with painful neurological conditions, as well as a valuable tool in the serial evaluation of patients to assess the outcome of any therapeutic and/or surgical intervention.