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Focal muscle atrophy, also known as focal muscular atrophy (FMA), is a condition that causes muscle wasting or thinning of muscle mass. It can be caused by various factors, including nerve damage, nerve dysfunction, immobility, aging, malnutrition, medications, or injuries and diseases that affect the musculoskeletal or nervous system. FMA can lead to muscle weakness and cause difficulty in performing daily tasks, such as opening jars, holding objects, or walking. The treatment for FMA depends on the underlying cause and may include exercise, nutritional therapy, and molecular strategies like gene transfer to promote muscle regeneration.
| Characteristics | Values |
|---|---|
| Definition | Focal atrophy of an individual muscle or group of muscles |
| Prevalence | No overall prevalence rates are available due to the heterogenous nature of the disorder |
| Causes | Neurogenic conditions, disuse of muscles, malnutrition, age, genetics, lack of physical activity, certain medical conditions |
| Symptoms | Decrease in muscle mass, one limb being smaller than the other, numbness, weakness, tingling in limbs, difficulty swallowing or speaking |
| Diagnosis | Physical exam, blood test, muscle or nerve biopsy, electromyography (EMG), nerve conduction studies, CT scan, MRI scan |
| Treatment | Physical therapy, occupational therapy, routine exercise, immunosuppressive therapy |
| Prognosis | Benign, does not affect lifespan |
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What You'll Learn
- Focal muscular atrophy (FMA) is caused by several anomalies that affect the LMN
- FMA is characterised by muscle wasting and weakness
- FMA can be caused by polio or monomelic amyotrophy
- FMA can be treated with exercise and a healthy diet
- Focal nerve injuries can be treated with molecular strategies such as gene transfer
Focal muscular atrophy (FMA) is caused by several anomalies that affect the LMN
Focal muscular atrophy (FMA) is a condition that causes muscle wasting and can be caused by several anomalies that affect the LMN. FMA is characterised by asymmetric weakness and/or atrophy in muscles, with muscle twitching, cramping and pain also being common symptoms. The onset of FMA can be insidious, with muscle wasting as the presenting symptom, or more abrupt, with muscle weakness being the primary symptom.
There are two main types of muscle atrophy: disuse (physiologic) atrophy and neurogenic atrophy. Disuse atrophy occurs when muscles are not used enough, which can be due to a sedentary lifestyle, malnourishment, old age, or certain medical conditions such as a stroke. Neurogenic atrophy, on the other hand, is caused by nerve problems or diseases that affect the nerves connecting to the muscles. This can include nerve injury, trauma, or compression, as well as diseases of the muscles such as muscular dystrophy or myopathies.
FMA specifically can be caused by a variety of anomalies that affect the LMN. These include poliolike viruses, paraneoplastic anomalies, and bulbar palsy due to ALS. Poliolike viruses can cause neuronopathy following acute hemorrhagic conjunctivitis, for example, the EV70 virus. Paraneoplastic anomalies are associated with cancer or lymphoma, especially Hodgkin's disease. Lastly, bulbar palsy due to ALS eventually leads to limb involvement in most cases, although this is rare initially.
In addition to these causes, FMA has also been linked to degenerative, infectious, and ischemic mechanisms. For instance, in India, Korea, and Japan, FMA is termed benign focal amyotrophy, Hirayama disease, or wasted leg syndrome, and is thought to be caused by repeated compression of the dura and spinal cord during neck flexion, leading to ischemic myelopathy.
Although the diseases that cause FMA are typically self-limiting and benign, they can significantly impact an individual's quality of life. Treatment options are limited, but they may include exercise, a healthy diet, and nutritional therapy.
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FMA is characterised by muscle wasting and weakness
Focal Muscular Atrophy (FMA) is a condition that causes muscle wasting and weakness. It can be caused by various anomalies affecting the lower motor neuron (LMN). FMA often arises from nerve damage or dysfunction, which inhibits muscle contractions and results in muscle wasting. The hallmark sign of FMA is the loss of lean muscle mass, which can be difficult to detect due to obesity, changes in fat mass, or oedema.
Muscle wasting is typically the presenting symptom of FMA, with weakness being more prevalent when the onset is abrupt. Proximal weakness in the upper limbs may manifest as difficulty raising the arms or reaching for high objects, while weakness in the lower limb muscles can lead to challenges in walking, climbing stairs, navigating uneven surfaces, and stumbling over small objects.
The rate of muscle atrophy can vary, with disuse atrophy occurring within two to three weeks of immobilisation. The elderly are particularly vulnerable to rapid muscle loss with immobility. In addition to immobility, ageing, malnutrition, medications, and various injuries or diseases affecting the musculoskeletal or nervous system can contribute to muscle atrophy.
FMA can be treated with exercise and a healthy diet, and in some cases, anabolic agents may be considered. Molecular strategies such as gene transfer can also promote muscle regeneration and enhance muscle bulk, strength, and functional activity.
While FMA can cause significant muscle wasting and weakness, it is important to note that the diseases leading to FMA are mostly self-limiting and benign, and they do not affect the lifespan of the individual.
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FMA can be caused by polio or monomelic amyotrophy
Focal muscular atrophy (FMA) is characterised by muscle wasting and weakness. It can arise from several anomalies that affect the lower motor neuron (LMN). FMA can be caused by polio or monomelic amyotrophy (MMA).
Polio is a highly contagious virus that affects nerve cells called motor neurons, which carry messages between the brain and muscles. Motor neurons in the spinal cord are particularly affected by the poliovirus. An initial polio infection can lead to post-polio syndrome (PPS), a condition causing gradual muscle weakness and atrophy. PPS usually occurs 10 to 40 years after recovery from the initial polio infection. The condition is rarely life-threatening, but severe muscle weakness can lead to falls, fatigue, pain, and difficulty with breathing and swallowing.
Monomelic amyotrophy (MMA) is a rare disease characterised by muscular weakness and wasting in the distal upper extremities, beginning in adolescence. MMA affects the lower motor neurons, which help communicate information from the brain to the muscles involved in movement. MMA causes weakness and loss of muscle mass in the arms and fingers, with no associated pain or sensory changes. MMA is most common in Asia, especially in Japan and India, and is more prevalent in males than females. The exact cause of MMA is unknown, but it can sometimes run in families.
Both polio and monomelic amyotrophy are disorders that can cause FMA. While polio is a contagious viral infection, MMA is a rare disease with an unknown cause, though it may have a genetic component. PPS and MMA present with similar symptoms of muscle weakness and atrophy, though PPS can also cause muscle pain and respiratory issues. MMA affects the upper extremities, while PPS can affect muscles involved in breathing and swallowing.
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FMA can be treated with exercise and a healthy diet
Focal muscular atrophy (FMA) is a heterogeneous disorder with diverse etiologies, characterised by wasting or thinning of muscle mass. It can be caused by disuse of muscles or neurogenic conditions. FMA can arise from several anomalies that affect the lower motor neuron (LMN) or, at times, secondary to nonneurologic disorders. The organ ultimately affected is the muscle, although the pathology may be anywhere along the LMN.
Disuse atrophy can be caused by leading a sedentary lifestyle, malnourishment, having a desk job, or being on bed rest. It can be treated with exercise and a healthy diet. Your healthcare provider may start you on a programme that includes exercises in the pool, as working out in the water can reduce your muscle workload. They may also recommend physical therapy or an exercise plan, and suggest nutritional supplements.
Neurogenic atrophy, on the other hand, is caused by an injury or disease affecting nerves that connect to your muscles. When these nerves are damaged, they cannot trigger the muscle contractions needed to stimulate muscle activity. Unfortunately, neurogenic atrophy typically cannot be reversed because of the physical damage that has been done to the nerves. However, it can sometimes be treated with a special kind of physical therapy called electrical stimulation.
Treatment of FMA varies according to the cause. When patients with these conditions have disabilities, the treatment consists of physical and occupational therapy and rehabilitation.
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Focal nerve injuries can be treated with molecular strategies such as gene transfer
Focal muscle atrophy (FMA) is a heterogeneous disorder with diverse etiologies and various signs and symptoms. It can be caused by several anomalies that affect the lower motor neuron (LMN) and can be secondary to non-neurologic disorders. FMA often presents as muscle wasting or atrophy, which can be restricted to a single limb or part of a limb. This can lead to weakness and functional difficulties, such as opening jars, typing, or walking.
Focal nerve injuries, a common cause of muscle loss, can result in poor muscle repair or regeneration, leading to functional impairment. However, molecular strategies, such as gene transfer, offer promising treatment options for focal nerve injuries and subsequent muscle atrophy.
Gene therapy has been successfully employed in animal models of optic nerve diseases, such as glaucoma, optic neuritis, and Leber's hereditary optic neuropathy (LHON). For instance, gene therapy using adeno-associated virus (AAV) vectors has demonstrated significant neuroprotective effects in a rat model of glaucoma. Similarly, AAV-mediated gene therapy has been used to replace defective mitochondrial enzymes in cells derived from LHON patients. These studies highlight the potential of gene therapy in treating focal nerve injuries and promoting regeneration and functional recovery.
Molecular strategies targeting the nuclear factor kB (NF-kB) pathway have also been explored in the context of muscle atrophy caused by focal nerve injury. NF-kB activation is elevated in denervated muscles, leading to skeletal muscle atrophy by inhibiting new muscle formation and enhancing the breakdown of existing muscle. Researchers have developed serotype 8 adeno-associated viral vectors (AAV8) carrying expression cassettes designed to inhibit pathological NF-kB activation, which may improve muscle bulk and strength.
Additionally, stem cell therapy, combined with gene therapy or biomaterials, could further enhance the regeneration of damaged neurons. While current strategies face limitations, such as low cell survival rates, innovative approaches like nanostructured biomaterials and in vivo gene expression reprogramming show promising results in promoting neural regeneration and repair.
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Frequently asked questions
Focal muscle atrophy (FMA) is the wasting or thinning of muscle mass in a single limb or part of a limb. It can be caused by nerve damage, nerve dysfunction, disuse of muscles, or neurogenic conditions.
Symptoms of focal muscle atrophy include muscle weakness, decrease in muscle mass, one limb being smaller than the other, and numbness, weakness and tingling in the limbs.
Focal muscle atrophy can be caused by nerve injury, trauma, or compression. It can also be caused by immobility, aging, malnutrition, medications, or a wide range of injuries or diseases that impact the musculoskeletal or nervous system.
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