EMG diagnostics in neuromuscular disorders
Electromyography – EMG is performed to evaluate functional state of peripheral nervous system and muscular system.
EMG consists of:
Peripheral nerve conduction test
The aim of this examination is to determine the velocity of conduction in a nerve, the degree and type of nerve damage and, indirectly, the reason of a damage. Stimulus is triggered off with a bipolar stimulating electrode (surface electrode) on the surface of the skin over the area of anatomical peripheral nerve course. Stimulus intensity and time of duration depends on whole nerve fibres excitability up to the moment of formation of action potential of highest possible amplitude value.
The aim of this examination is to evaluate functionality of a muscle in rest, during routine movement and during maximal effort. This examination is performed with a needle electrode , which is inserted directly into the examined muscle. Motor unit parameters: amplitude, time of duration, area and size index are used to muscle assessment and enable diagnostics of neuropathic or myopathic process.
Neuromuscular transmission (repetitive nerve stimulation RNS, fatigability test)
The aim of this examination is to evaluate neuromuscular conduction after stimulation with supramaximal stimuli. Evaluation of amplitude values 4:1 enables detection of neuromuscular conduction abnormalities due to, for example, myasthenia. This examination is performed with surface electrodes attached to the skin over the muscle of stimulated nerve.
Neuromuscular hyperexcitability (tetany test, ischaemic test)
This examination is performed with needle electrode, which is inserted into the first dorsal interosseus muscle, and with an elastic cuff, which is wrapped around the patient’s arm for 10 minutes. During the last 2 minutes of the examination the patient is hyperventilating. After removing the elastic cuff discharges characteristic for tetany can be observed.
EMG EXAMINATION IS ESSENTIAL IN THE DIAGNOSTICS OF UNDERMENTIONED DISEASES
- Neuromuscular junction diseases (myasthenia, myasthenic syndrome)
- Polyneuropathies of different causes (diabetic neuropathy, toxic, inflammatory neuropathy, Guillian-Barre syndrome, CIDP)
- Single peripheral nerves neuropathy due to pressure or injury (carpal tunnel syndrome, tarsal tunnel syndrome)
- Neural plexuses injuries (brachial plexus injury, lumbosacral plexus injury)
- Motor neuron damage (SLA amyotrophic lateral sclerosis)
- Neuromuscular hyperexcitability syndrome (tetany)
- Poly-muscular damage of different causes (toxic, for example drug-induced, metabolic, for example hypothyroidism, genetically determined inflammation)
- Single muscles damage due to injury
- Radicular syndromes – cervical and lumbosacral (brachialgia, ischialgia) especially with strong pain and deficit symptoms
- Evaluation of muscle tension (stiffness syndromes of different causes), hypertonia (spasticity) due to neural diseases
INFORMATION ABOUT EXAMINATIONS
- Conduction in motor and sensory nerve fibres + F wave. Non-invasive examination, usually well tolerated by the patient. The aim of the examination is to evaluate conduction velocity in motor and sensory peripheral nerve fibres. It enables evaluation of both the nerve damage degree and its character. Supramaximal electric stimulus is used for stimulation in several areas of anatomical nerve course.
- Examination is performed with needle electrode, it helps to determine level and kind of a damage. This examination may be painful, minor, usually transient pain may be felt also after the examination.
- Partial ulnar nerve examination, between medial and lateral epicondyle of humerus, enabling evaluation of a damage level (nerve compression in ULNAR NERVE GROOVE). It is a subsidiary examination of ulnar nerve (SURFACE ELECTRODE)
- H (Hoffmann) reflex – monosynaptic spinal reflex used in the diagnostics of S1 radiculopathy due to the ease of its obtaining from lower limb muscles. It eases differentiation with the damage of L5 nerve root and is helpful especially in case of monolateral radicular damage. Advantage of obtaining H reflex in radicular syndromes is a possibility of demonstrating sensory fibres damage and the fact, that this reflex becomes changed on the early stages of the disease, and changes last as long as compression process. Usability of H reflex is limited by small number of muscles, from which it can be obtained; in a routine practise those are only lower limb muscles (S1 nerve root). H reflex can be preserved in case of partial root damage, and absent in other diseases and in people over 60.
- Fatigability test – consists in repetitive stimulation of weak (fatigue) muscle nerve. It’s used in neuromuscular junction diseases like: myasthenia, Lambert-Eaton syndrome, congenital myasthenic syndrome, botulism poisoning.
- Short branches of brachial plexus (SURFACE ELECTRODE) – nerves beginning from supraclavicular and infraclavicular part of brachial plexus. The time of conduction (standardised latency) is evaluated with reference to 3 nerves: radial nerve (triceps brachii muscle), musculocutaneous nerve (biceps brachii nerve) and axillary nerve (deltoid muscle). It is also possible to examine other short nerves of the plexus: dorsal scapular nerve, long thoracic nerve, suprascapular nerve, subscapular nerve)
- Examination of brachial plexus – examination of long and short nerves and respective muscles according to the level of a damage (SURFACE AND NEEDLE ELECTRODE)
- Tetany test – the examination lasts about 15 minutes. Patient’s blood pressure is measured, and then a pressure cuff is inflated about 20-30 mmHg above systolic pressure. Next, a needle electrode is inserted into the first dorsal interosseus muscle (between the thumb and index finger). In the 8th minute of the examination intensive breathing is added (so called hyperventilation), which lasts up to 10th minute of the examination, next the cuff is released and a monitor is observed. If the test is positive, multiplet discharges characteristic for tetany, are visible on the monitor. The examination helps to diagnose both manifest and latent tetany.
- Diagnostics of facial nerve damage. Examination performed to evaluate time of conduction in a facial nerve (peripheral part). Depending on the level of a damage it can be performed to register data from 3 muscles: frontal muscle, orbicularis oculi muscle or orbicularis oris muscle. Allows to confirm peripheral character of the damage of facial nerve (surface electrode).
- Blink reflex – bilateral constriction of orbicularis oculi muscles after electrical stimulus being applied monolaterally to the supraocular area. Examination enables evaluation of intracranial parts of nerves V and VII function (surface electrode).
- Examination for myopathy. Examination consists in basic neural conduction examinations (surface electrode).
- Examination of proximal muscles with needle electrode for evaluation of rest activity, motor unit potentials during routine limb movements and analysis of effort electromyogram. Examination for polyneuropathy – consists in conduction in upper and lower limb nerves. Depending on kind of changes in examined nerves – axonal process, demyelinating or mixed process, additional examination with needle electrode should be performed (usually performed in case of axonal changes in examined nerves).
- Examination for motor neuron disease – conduction in upper and lower limb nerves, and examination of distal and proximal upper and lower limbs muscles and, additionally, of tongue muscle and paraspinal muscles.
- Examination for Guyon’s canal syndrome. Standard ulnar nerve examination with pressure to distal damage location.
- Additionally, midsgittal nerve examination is performed to eliminate generalised disease. Additional diagnostic tests are performed to determine damage location and type. Ulnar nerve can be pressed in any part of the Guyon’s canal leading to sensory, motor or sensory-motor deficits.
- Examination for tarsal tunnel syndrome. This syndrome is a compression neuropathy of tibial nerve, it can affect nerve trunk or its plantar or calcaneal branches. Apart from neurological examination, EMG is essential to diagnose the syndrome. Routinely, neurographic examination of motor and sensory fibres of tibial nerve together with one of the nerves outside tarsal canal (for example peroneal nerve) is performed (SURFACE ELECTRODE). If neurographic examination indicates, that damage area is located inside tarsal canal, examination of inner foot muscles can be performed to confirm the diagnosis or evaluate the process activity.
- Examination for carpal tunnel syndrome. CTS – carpal tunnel syndrome is the most frequent compression mononeuropathy. Differential diagnosis should exclude other diseases of similar symptoms, like: pronator teres syndrome, anterior interosseus syndrome, thoracic outlet syndrome (TOS), ulnar nerve neuropathy, superficial radial nerve neuropathy, or early stage of polyneyropathy. Routinely sensory-motor conduction of median and ulnar nerves is performed. In case of doubts, additional diagnostic test are recommended to help to confirm the diagnosis.
PREPARATION FOR THE EXAMINATION
- The examination does not require any special preparation but it is recommended that before the examination no creams or balms are used on examination area.
- In winter, it is recommended to warm up the examination area before the examination, especially during electroneurography.
- It is recommended to discontinue taking vitamin complexes few days before tetany test, as they may influence the test result.
- The patient should get undressed before the examination. Sometimes, it is enough to roll up the sleeves above the elbow, in other cases, the patient has to be in underwear only.
- Most examinations are performed when the patient is lying down. The time of examination depends on the type of examination, the number of examined nerves or muscles and cooperation of the patient during the examination.
- In case of examinations with needle electrode the patient should discontinue taking acenocumarol-like drugs (that influence INR) at least 3 days before the examination, and, after doctor’s consultation and dose adjustment, should start taking low-molecular-weight heparin. Low-molecular-weight heparins (clexane, fraxiparine) should not be taken.
- In case of pacemaker, cardioverter defibrillator, a cardiologist’s permission is necessary before the full examination.
- A barrier to the examination performance may be constant orthopaedic supply, for example cast that makes impossible to reach the examined limb with electrodes or numerous prostheses, foreign bodies in examined limbs (which can interfere with examination result and impede the result assessment).
- The patient has to wait for the result for 1 day.
For every examination due to pressure, another imaging, such as ultrasound or MRI should be made.
To register for the examination and get detailed information call +48 (22) 566 22 22.