Victor Forge
Muscle fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. The first recorded observations of muscle fibrillations were reported by Schiff in 1851, who observed fibrillations in the tongue muscles of dogs. Fibrillations are spontaneous depolarizations of the membrane of individual muscle fibres that result in contraction. They occur when a muscle fibre is disconnected from the motor neuron, resulting in the loss of electrical and chemical stimuli. Fibrillations can be detected by electrodiagnostic testing, such as electromyography (EMG), which measures the electrical activity of skeletal muscles. While muscle fibrillations do not typically cause serious health issues, they can be indicative of axonal loss in peripheral nerve disorders or primary muscle diseases such as polymyositis and muscular dystrophy.
| Characteristics | Values |
|---|---|
| Definition | The rapid, irregular, and unsynchronized contraction of muscle fibers |
| Types | Two major classes of cardiac fibrillation: atrial fibrillation and ventricular fibrillation |
| Atrial Fibrillation | An irregular and uncoordinated contraction of the cardiac muscle of atria |
| Atrial Fibrillation Treatment | Usually treated with anticoagulation and sometimes with conversion to normal sinus rhythm |
| Ventricular Fibrillation | An irregular and uncoordinated contraction of the cardiac muscle of ventricles |
| Ventricular Fibrillation Outcome | Usually fatal if not reversed by defibrillation |
| Cause | The spontaneous firing of a single muscle fiber when it is disconnected from the motor neuron |
| Detection | Not visible through the skin surface, detectable by electrodiagnostic testing like electromyography (EMG) and Dynamic Echomyography (DyEM) |
| Fibrillation Appearance on Ultrasound | Small, irregularly oscillating movements of muscle tissue in all directions, while the overall shape of the muscle is preserved |
| Ultrasound Sensitivity | Depends on the amount of fibrillations present and limb temperature |
| Fibrillation Potentials | Not diagnostic of denervation as they can occur in primary muscle diseases like polymyositis and muscular dystrophy |
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What You'll Learn
- Muscle fibrillation is not visible through the skin surface
- Fibrillation is caused by the spontaneous firing of a single muscle fibre
- Fibrillation can be detected by electrodiagnostic testing
- Fibrillation can be a sign of axonal loss in peripheral nerve disorders
- Fibrillation can be treated with electrical muscle stimulation
Muscle fibrillation is not visible through the skin surface
Muscle fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. It is the spontaneous firing of a single muscle fibre, which results when a muscle fibre is disconnected from the motor neuron.
Fibrillation of skeletal muscle is not visible through the skin surface. It can only be detected by electrodiagnostic testing, such as electromyography (EMG), which measures the electrical activity of skeletal muscles. On an EMG, fibrillation appears as a low-amplitude, short-duration potential with an initial negative deflection. Fibrillation typically repeats in a rhythmic pattern but can also occur irregularly.
EMG is useful in determining the progress, prognosis, and efficacy of therapeutic interventions, particularly for patients with peripheral nerve injury. However, EMG may miss focal areas with fibrillations within a muscle due to sampling error. In such cases, ultrasound techniques can be used to visualise fibrillations, appearing as small, irregularly oscillating movements of muscle tissue in all directions while preserving the overall shape of the muscle.
While muscle fibrillation is not visible through the skin, fasciculations, which are also spontaneous contractions, can be seen. These involve small groups of muscle fibres and can be observed in lower motor neuron lesions.
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Fibrillation is caused by the spontaneous firing of a single muscle fibre
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. It is caused by the spontaneous firing of a single muscle fibre, which occurs when a muscle fibre is disconnected from its motor neuron. This disconnection results in the loss of electrical stimulus and any chemical "neurotrophic" factors the nerve would have supplied.
The first recorded observations of muscle fibrillations after denervation were reported by Schiff in 1851, who observed fibrillations in the tongue muscles of dogs after bilateral hypoglossal nerve section. Later, in 1915, Langley and Kato explicitly showed that fibrillations followed denervation. Fibrillations typically repeat in a rhythmic pattern but can also occur irregularly. They appear on ultrasound videos as small, irregular oscillating movements of muscle tissue in all directions, while the overall shape of the muscle is preserved.
Electromyography (EMG) is a useful tool for detecting fibrillations, as it measures the electrical activity of skeletal muscles. Fibrillations show up as very tiny electrical impulses on EMGs, in contrast to fasciculations, which show large impulses. However, EMG may miss focal areas with fibrillations within a muscle, and newer ultrasound techniques with better resolution and higher frame rates have been developed to visualize fibrillations.
The exact mechanism producing fibrillations is not known, but several hypotheses have been proposed. Fibrillating muscle fibres have local segments of abnormal muscle fibre membrane, which are probably not more than millimetres in length. These abnormal regions are the origin of fibrillation potentials and most often occur near the neuromuscular junction but can occur anywhere along the length of the muscle fibre. These spontaneous depolarizations of the membrane may be caused by altered sodium conductance in the abnormal segment of the membrane.
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Fibrillation can be detected by electrodiagnostic testing
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. It occurs when a muscle fibre is disconnected from the motor neuron. Fibrillation can be detected by electrodiagnostic testing, which consists of nerve conduction studies and needle electrode examination. This form of testing helps to precisely locate disease processes affecting the peripheral nervous system and has limited use in the evaluation of central nervous system disorders. Electrodiagnostic testing is considered an extension of the physical examination and is most useful in the workup of conditions such as carpal tunnel syndrome, ulnar neuropathy, and tarsal tunnel syndrome.
Electrodiagnostic testing can be performed on multiple muscles, typically between 6 and 15 muscles. An electrode is inserted into the muscle belly to record electrical activity at rest and during voluntary contraction. Abnormal spontaneous activity in the form of fibrillation or positive sharp wave potentials signifies loss of muscle innervation, necrosis, or inflammation. During voluntary muscle activation, the needle electrode records the size, morphology, and firing pattern of a motor unit action potential.
Single fibre electromyography (SFEMG) is a type of electrodiagnostic testing that is particularly sensitive for detecting myasthenia gravis and other neuromuscular junction pathologies. It is also useful for assessing motor unit morphology in some neuromuscular diseases. Electromyography (EMG) is another valuable tool for determining progress, prognosis, and the efficacy of therapeutic interventions. EMG is also useful for detecting subclinical myopathy, assessing disease activity, and selecting a suitable muscle for biopsy.
While EMG is considered the gold standard for fibrillation detection, it can miss focal areas with fibrillations within a muscle due to sampling error. In such cases, ultrasound techniques can be advantageous as they can visualize larger areas of the muscle. Ultrasound detects fibrillations as small, irregularly oscillating movements of muscle tissue in all directions while preserving the overall shape of the muscle. However, the sensitivity of ultrasound for detecting fibrillations depends on factors such as the amount of fibrillations present and limb temperature.
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Fibrillation can be a sign of axonal loss in peripheral nerve disorders
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. It occurs when a muscle fibre is disconnected from the motor neuron, resulting in the spontaneous firing of a single muscle fibre. Fibrillations are not visible from the outside and can only be detected by electrodiagnostic testing, such as electromyography (EMG).
EMG is particularly useful in patients with peripheral nerve injuries, as it can help determine the progress, prognosis, and efficacy of therapeutic interventions. Peripheral nerve disorders, such as peripheral neuropathy, can result from various causes, including diabetes, alcohol use disorder, vitamin deficiencies, trauma, surgery, vascular disorders, and autoimmune conditions.
In the context of peripheral nerve disorders, fibrillation can indeed be a sign of axonal loss. Axonal degeneration is the most common pattern observed in peripheral neuropathy. When a muscle loses connection with its nerve, it loses both the electrical and chemical signals provided by the nerve. This disconnection results in the spontaneous contractions characteristic of fibrillation.
Research has shown that the onset of fibrillation potentials after axonal nerve injury typically occurs within 1 to 4 weeks, although this timeline may vary depending on the distance between the neural lesion and the muscle. The detection of fibrillations is important in understanding the progress and prognosis of peripheral nerve injuries and can guide therapeutic interventions to preserve muscle function and counteract atrophy.
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Fibrillation can be treated with electrical muscle stimulation
Fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres. This occurs when a muscle fibre is disconnected from the motor neuron. Fibrillation can be treated with electrical muscle stimulation, also known as transcutaneous electrical nerve stimulation (TENS). TENS uses a mild electrical current to treat pain and relieve muscle contractions.
The TENS unit is a battery-powered device with electrodes that deliver electrical impulses through the surface of the skin. The electrodes are placed at or near trigger points or affected nerves. The intensity, frequency, and duration of the pulses can be adjusted to suit the patient's needs. TENS therapy is usually used to ease pain during treatment, and it can be used to treat both acute and chronic conditions.
Electrical muscle stimulation has been shown to be effective in treating peripheral nerve injuries and preventing muscle atrophy. It can also be used to increase muscle strength, improve shoulder subluxation, and reduce muscle tone. For example, functional electrical stimulation (FES), a subtype of neuromuscular electrical stimulation (NMES), can be used to assist patients in performing functional movements such as standing, walking, and grasping objects.
FES has been shown to be particularly useful in helping individuals who have suffered a stroke or spinal cord injury regain their motor functions. The electrical discharges applied to the muscles allow them to contract in a sequence that enables the performance of various tasks. FES systems that facilitate specific movements are often referred to as neuroprostheses.
Additionally, electrical stimulation has been found to prevent the development of sensitivity to ACh in denervated rat muscles and cause ACh-sensitivity to disappear. This demonstrates that muscle sensitivity to ACh is dependent on electrical input rather than trophic factors contributed by the nerves.
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Frequently asked questions
Muscle fibrillation is the rapid, irregular, and unsynchronized contraction of muscle fibres.
Fibrillation occurs when a muscle fibre is disconnected from its motor neuron, resulting in the spontaneous firing of a single muscle fibre.
Fibrillation can be detected through electrodiagnostic testing, such as electromyography (EMG) or dynamic echomyography (DyEM). EMG is considered the gold standard for fibrillation detection, but it may miss focal areas of fibrillation within a muscle. Ultrasound techniques have also been used to visualise fibrillations, but their sensitivity depends on factors such as limb temperature and the amount of fibrillation present.
There are two main types of muscle fibrillation: rhythmic fibrillation and irregular fibrillation. Rhythmic fibrillation occurs regularly due to oscillating fluctuations in membrane potential, while irregular fibrillation results from random, spontaneous depolarization of abnormal segments in the muscle fibre.
