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BASIC PRINCIPLES OF ELECTRODIAGNOSTICS
- The human body constantly generates electrical energy. Specifi cally, the muscle and nerve cells constantly use electric discharges to communicate among different parts of the body.
- These electric discharges can be recorded, displayed, measured, and interpreted by using specialized equipment.
- In the presence of disease or injury, the architecture and normal processes of nerves and muscles are altered. Recognizing these changes can be useful for diagnosis, monitoring disease progression, and assessing treatments.
- Electrodiagnostic (EDX) medicine is the process of observing and interpreting neuromuscular electrical discharges for clinical purposes. We use “EDX” for the remainder of this book to represent this testing, which includes nerve conduction studies (NCS) and electromyography (EMG) .
BASIC LOGISTICAL DETAILS FOR YOUR FIRST DAY PERFORMING ELECTRODIAGNOSTICS
- The novice EDX consultant (from here on referred to as “you”) is faced with learning many new concepts in parallel and at once.
- These include the associated basic science concepts ( Table 1 . 1 ), hands-on EDX procedures, and analysis of the EDX results. The second basic concept—the hands-on EDX procedure – is the emphasis of this book.
- At fi rst, you will just perform the procedures of an algorithm accurately and effi ciently under the guidance of your instructor.
- Once your hands are moving easily from one procedure to the next, you should be able to spontaneously analyze on the fl y and mentally adjust a dynamic algorithm.
BASIC CONSTRUCTION OF AN ELECTRODIAGNOSTIC CONSULT
You will be consulted by a clinician who will send all types of chief complaints to “rule out” things. These usually include complaints of numbness, tingling, or weakness. You should view the referral simply as a guideline or starting point for the EDX visit.
The EDX encounter is different from a regular consult because the emphasis is placed on you as a technician. Therefore, you may want to be more focused and direct without sacrifi cing professionalism, compassion, or congeniality. Look for possible contraindications (see Box 3.3 in Chapter 3) prior to performing the procedure. Point out reasonable expectations of the test to your patients and warn them that it is uncomfortable but well tolerated by most people.
This is the time to establish a broad differential diagnosis. Try to fi gure out which body system is involved. Is the etiology neurological? Musculoskeletal? Psychological? Bilateral? Proximal versus distal?
At this time, you will essentially confi rm your thoughts using the history. This will inform and direct your EDX testing, which should never be set in stone.
Nerve Conduction Studies
Typically, this is the fi rst part of the EDX examination. You will stimulate nerves by delivering an electrical current usually via a stimulator wand. The axons of the stimulated nerve generate action potentials that propagate both proximally and distally from the site of stimulation. Electrodes placed over the nerve or a relevant muscle “pick up” the action potential as it propagates under them. The electrical signal that is picked up by the electrodes is amplifi ed, fi ltered, and processed by the equipment.