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Astute Clinical Neurological Assessment Must Precede EMG
By Albert L. Berarducci, Jr., M.D., A.B.P.N.
Electromyography or EMG is a respected technique that has matured through the years, gaining value as new technology has been adapted to it. It has maintained a high level of importance to specialists in neuromuscular disease.
However, EMG as a screening tool for pathology is not useful. Without insight from the clinical neurologic examination as a guide, information from the EMG may confuse the clinical picture, delaying eventual diagnosis and treatment.
Steady Improvement in Technology
Technology adapted to the EMG has steadily improved over the years. EMG was born almost at the same time as the discovery of electricity in the middle of the 19th century.
In the 1950s and 60s, computerization of the EMG study permitted electromyographers the opportunity to study small biogenic potentials averaged from routine electrical background "noise"--a quantum leap in capability. The advanced computing power of our newest EMG machines allows ever more sophisticated statistical analysis of even these small physiologic responses.
Insight Requires Coordinated Clinical Effort
From its earliest stages of development, EMG study has required that the neurological clinician and electromyographer work closely together. The clinician must frame the clinical questions as precisely as possible. The electromyographer must reformulate that question in electrophysiologic terms so the vast technical capacity of EMG will be most likely to clarify the answer to the clinical question. The clinician skilled at neurologic diagnosis and the electromyographer use similar logic but different disciplines in attacking a clinical problem. The neurological clinician defines the questions to be studied, while the electromyographer supplies the precision and objective detail in the answer.
For example, the clinician may know the general pattern of weak muscle groups. But the electromyographer can study atrophic, deeply situated muscles with the tip of an EMG needle that cannot be evaluated by even the best clinical examiners. The clinician may know which sensory fields are abnormal. But the electromyographer can study electrical parameters of small lengths of nerve to isolate the exact site of pathology.
The EMG can provide quantitative information about electrical reflexes (e.g. F-waves, H-reflexes, Blink Reflex, etc.) invisible to the neurological clinician. Abnormalities may even be found in these reflexes by EMG testing even if they are normal in the clinical neurological examination. The electromyographer can analyze parts of the peripheral nervous system (PNS), such as the neuromuscular junction, in which the neurological clinician may only suspect abnormality.
Prior Clinical Exam Essential
Fruitful EMG study of the PNS requires a close partnership between the clinician and the neurophysiologist. EMG should not be done in the absence of a good clinical neurological assessment of the problem. The capabilities and skill of the electromyographer are blunted without prior, astute clinical neurological examination to outline the field of study for the electromyographer.
Focused in this way, the EMG is most powerful. Just as pictures taken by the Hubbell space telescope need a series of lenses to sharpen the image, EMG used without the pathfinding help of a careful neurological examination is merely data without understanding.
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