Victor Forge
Symmetrical muscle wasting, or symmetric weakness, is a common complaint among patients presenting to family physicians. It is characterised by muscle atrophy, or wasting, that affects both sides of the body evenly. The most common pattern of symmetrical muscle wasting in myopathies predominantly affects the proximal muscles of the legs and arms, or the so-called limb-girdle distribution. This pattern of weakness is seen in most hereditary and acquired myopathies. Determining the cause of symmetrical muscle wasting involves distinguishing primary weakness from fatigue or asthenia, which are common conditions that differ from, but often overlap with, muscle weakness.
| Characteristics | Values |
|---|---|
| Definition | Symmetrical muscle wasting is a common sign of muscle atrophy, which can be difficult to detect, especially in older adults. |
| Common Causes | Hereditary and acquired myopathies, cardiac cachexia, CHF, endocrine changes, metabolic changes, inflammatory and rheumatologic myopathies, neurogenic disorders, neuromuscular junction disorders, CNS lesions, peripheral nerve compression or inflammation, systemic processes, and infectious diseases. |
| Symptoms | Muscle weakness, difficulty walking, climbing stairs, or performing fine motor tasks, leg bowing, pseudofractures, joint swelling, exercise intolerance, respiratory muscle weakness, and increased morbidity and mortality. |
| Diagnosis | Patient history, physical examination, neurological examination, laboratory testing, genetic testing, blood chemistries, thyroid-stimulating hormone assay, creatine kinase level, antinuclear antibody assays, biopsy, and pathologic evaluation of muscle tissue. |
| Treatment | No specific treatment mentioned, but early diagnosis and management of underlying causes may help improve outcomes. |
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What You'll Learn
Myopathies and muscle weakness
Myopathies refer to diseases that affect skeletal muscles—those that connect to bones and enable voluntary movement. Myopathies cause muscle weakness due to a dysfunction of the muscle fibres. The most common pattern of muscle weakness in myopathies is symmetric weakness, predominantly affecting the proximal muscles of the legs and arms, or the so-called "limb-girdle" distribution. The distal muscles are usually involved, but to a much lesser extent.
Myopathies can be categorized as inherited or acquired. Inherited myopathies are those that are passed down genetically, often from inheriting an abnormal gene mutation from a parent. Congenital myopathies are a type of inherited myopathy and are somewhat unique compared to other types, as muscle weakness affects all muscles and is often non-progressive. Mitochondrial myopathy is caused by a defect in the mitochondria, which are the energy-producing part of cells. Metabolic myopathies are caused by defects in genes that code for enzymes needed for normal muscle function and movement. They often manifest as exercise intolerance, exertional muscle pains in the shoulders and thighs, or non-traumatic rhabdomyolysis.
Acquired myopathies develop later in life and can be due to other medical disorders, infections, exposure to certain medications, or electrolyte imbalances, among other possibilities. Autoimmune/inflammatory myopathies are diseases in which the body attacks itself, causing problems with muscle function. Toxic myopathy happens when a toxin or medication interferes with muscle structure or function. Toxins include alcohol and toluene, a vapor found in spray paint and other inhalants.
The facial muscles are typically spared in myopathies, and involvement of other muscles is extremely variable. In addition, the weakness is often asymmetric between the two sides, which is uncommon in most myopathies. This pattern is indicative of inclusion body myositis. Myotonic dystrophy may also present with symmetric muscle weakness.
Diagnosing myopathies can be challenging, and careful consideration of the distribution of muscle weakness and attention to common patterns of involvement in the context of other aspects of the neurologic examination and laboratory evaluation can assist in making a timely and accurate diagnosis. Over the past decade, genetic testing has also become an option for diagnosing myopathies, although it is often extremely expensive and not always covered by insurance.
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Muscle wasting and atrophy
Muscle weakness is a common complaint among patients, and it can be challenging to distinguish weakness from fatigue or asthenia, which are separate conditions with different etiologies that can coexist with or be mistaken for weakness. The pattern and distribution of muscle wasting and weakness can help localize the lesion to a peripheral nerve, plexus, or root. For example, in cases of anterior horn or proximal root involvement, fasciculation may occur. The distribution of sensory loss can also aid in localizing the lesion. Deep tendon reflexes (DTRs) may be brisk or exaggerated in spinal lesions or in ALS, but they may be absent in root/plexus/nerve lesions.
The diagnosis of muscle wasting and atrophy begins with a comprehensive evaluation, including a thorough examination and coordination of laboratory, radiologic, electrodiagnostic, and pathologic studies. Electromyography may be used to confirm the presence of a myopathy or evaluate for a neuropathy or neuromuscular junction disorder. Laboratory studies may include blood chemistries, thyroid-stimulating hormone assays, creatine kinase levels, and antinuclear antibody assays to evaluate for various causes, such as electrolyte, endocrine, rheumatologic, inflammatory, genetic, or metabolic issues. In some cases, a muscle biopsy may be necessary for diagnosis, involving histologic, histochemical, electron microscopic, biochemical, and genetic analyses.
The pattern of muscle weakness can provide important clues about the underlying condition. For example, in most hereditary and acquired myopathies, symmetric weakness affecting the proximal muscles of the legs and arms is commonly seen, although distal muscles may also be involved to a lesser extent. On the other hand, asymmetric weakness is more typical of inclusion body myositis and some cases of myotonic dystrophy. Focal muscular atrophy of an individual muscle or group of muscles may also be observed and can present diagnostic and therapeutic challenges, as it can be associated with various neurologic disorders.
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Diagnosis and treatment
Symmetrical muscle wasting, or muscle atrophy, is the wasting or thinning of muscle mass. It can be caused by disuse of muscles or neurogenic conditions. The diagnosis of muscle weakness can be challenging and must be differentiated from subjective fatigue or pain-related motor impairment with normal motor strength. A physical examination is crucial to diagnosing the cause of muscle weakness. The patient's medical history, along with physical examination and diagnostic tests, will help determine the cause of muscle wasting.
To diagnose muscle atrophy, a healthcare provider will give the patient a physical exam and ask about their symptoms. They will look at the patient's arms and legs and measure their muscle mass. The healthcare provider may also order tests, including blood tests, muscle or nerve biopsies, electromyography (EMG), nerve conduction studies, computed tomography (CT) scans, and magnetic resonance imaging (MRI) scans.
The treatment of muscle atrophy depends on the type of atrophy. Disuse (physiologic) atrophy can be treated with regular exercise, a healthy diet, and physical therapy. A healthcare provider may recommend an exercise plan that includes exercises in the pool to reduce the patient's muscle workload. They may also suggest nutritional supplements. Neurogenic atrophy, on the other hand, typically cannot be reversed due to the physical damage done to the nerves. However, it can sometimes be treated with a special kind of physical therapy called electrical stimulation.
In some cases, muscle wasting can be improved or reversed with the right interventions, such as physical therapy, exercise, and a nutritious diet. It is important to address any underlying medical conditions that may be causing the muscle wasting. Ultrasound therapy is a non-invasive procedure that can aid in healing. If tendons, ligaments, skin, or muscles are too tight and prevent movement, surgery may be necessary.
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Causes and risk factors
Symmetrical muscle wasting, or symmetric weakness, is a common complaint among patients. It is characterised by symmetric causes of weakness arising from peripheral nerve, neuromuscular junction (NMJ), or intrinsic muscular disorders. CNS or UMN diseases are uncommon causes of symmetric weakness.
The causes of symmetrical muscle wasting are varied and can be challenging to diagnose. A comprehensive evaluation of patients includes a thorough examination and coordination of appropriate laboratory, radiologic, electrodiagnostic, and pathologic studies. Determining the cause of muscle weakness involves distinguishing primary weakness from fatigue or asthenia, which are common conditions that differ from, but often overlap with, muscle weakness.
Symmetric muscle weakness can be caused by hereditary and acquired myopathies. The most common pattern of muscle weakness in myopathies affects the proximal muscles of the legs and arms, or the "limb-girdle" distribution. The distal muscles are usually involved but to a lesser extent. The facial muscles are typically spared, and weakness is often asymmetric between the two sides, which is uncommon in most myopathies.
The CK level may be a determining factor in distinguishing different forms of muscular dystrophy. For example, in Duchenne dystrophy, the CK is at least 10 times normal, whereas in most other myopathies, there are less significant elevations. CK levels may be lowered by factors including profound muscle wasting, corticosteroid administration, collagen diseases, alcoholism, or hyperthyroidism.
Pulmonary testing may reveal the crackles of a restrictive lung defect, found in some inflammatory and rheumatologic myopathies. Gastrointestinal examination may reveal hepatomegaly, associated with metabolic storage diseases and amyloidosis. Skin findings are possible in multiple disease categories (e.g., skin bronzing in adrenal insufficiency; Gottron’s papules and heliotrope rash in dermatomyositis; and erythema nodosum in sarcoidosis).
Symmetric muscle weakness can also be caused by systemic diseases such as TSH, cortisol level, CK and aldolase, serum electrolytes, and autoimmune tests if an inflammatory source is suspected. Localized atrophy is more characteristic of a mechanical tendon or muscle problem or nerve entrapment.
In the case of focal muscular atrophy (FMA), the genetic profile is highly heterogeneous when hereditary. Associated features, such as gynecomastia and testicular atrophy in bulbospinal muscular atrophy or pes cavus in distal SMA, may help pinpoint the diagnosis of subtypes.
Overall, the determination of symmetric versus asymmetric weakness is a critical first step in identifying the underlying cause of muscle wasting.
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Progression and complications
Symmetrical muscle wasting, or muscle atrophy, is the wasting or thinning of muscle mass, resulting in muscles looking smaller than normal. It can be caused by disuse of muscles or neurogenic conditions. The progression and complications of symmetrical muscle wasting vary depending on the cause and type of muscle atrophy.
Disuse (Physiologic) Atrophy
Disuse atrophy occurs when muscles are not used enough, leading to a decrease in size and strength. This can be caused by leading a sedentary lifestyle, malnutrition, age-related factors, or certain medical conditions that limit mobility, such as stroke or injuries. The process of disuse atrophy can start within two to three weeks of muscle disuse. It can be reversed through exercise and a healthy diet, with specific exercises depending on the individual's condition.
Neurogenic Atrophy
Neurogenic atrophy is caused by nerve problems or diseases that damage the nerves connecting to the muscles. This damage impairs the nerve's ability to trigger the muscle contractions necessary for stimulating muscle activity. Neurogenic atrophy may develop sooner depending on the individual's health condition.
Muscular Dystrophy
Muscular dystrophy (MD) is a group of inherited diseases that cause progressive weakness and degeneration of skeletal muscles. There are more than 30 types of MD, with varying ages of onset, severity, and patterns of affected muscles. MD grows worse over time, and many individuals with MD eventually lose the ability to walk. Some types of MD also affect other organs, such as the heart, lungs, and gastrointestinal system. The progression of MD can lead to significant muscle weakness and loss of independence in performing daily tasks.
Spinal Muscular Atrophy (SMA)
SMA is a group of inherited diseases characterized by damage and death of motor nerve cells, leading to widespread, symmetric muscle weakness. There are five types of SMA, varying in age of onset and severity. SMA type 0 is the most severe form, affecting fetuses before birth. SMA type 4 is the mildest form, typically manifesting during adulthood. The progression of SMA results in worsening muscle weakness and wasting over time.
Amyotrophic Lateral Sclerosis (ALS)
ALS is a neurological condition causing skeletal muscle wasting due to the death of motor neurons. It typically affects individuals between the ages of 55 and 75, with symptoms steadily worsening over time. The hallmark symptom of ALS is progressive muscle weakness, leading to muscle wasting, twitching, and paralysis. ALS is a fatal disease, with individuals usually surviving only a few years after detection.
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Frequently asked questions
Symmetrical muscle wasting is a type of muscle atrophy that affects muscles on both sides of the body equally. It can be caused by a variety of neurological disorders and can affect the legs and arms, neck muscles, and in rare cases, the facial muscles.
The symptoms of symmetrical muscle wasting include muscle weakness, which can manifest as difficulty walking, climbing stairs, or performing fine motor tasks with the hands. Patients may also experience fatigue and asthenia, which is a sense of exhaustion.
The diagnosis of symmetrical muscle wasting begins with a thorough patient history and physical examination, including a neurologic survey. Laboratory tests such as blood chemistries, thyroid function tests, and creatine kinase levels may be ordered to evaluate for potential causes. Electromyography and muscle biopsies can also be used to confirm a diagnosis of symmetrical muscle wasting.
Treatment options for symmetrical muscle wasting depend on the underlying cause and may include physical therapy, medication, or other interventions. In some cases, early diagnosis and intervention can help slow the progression of the condition and improve patient outcomes.
