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Distal limb muscles are those that are farther away from the centre of the body, such as those in the hands and feet. Proximal muscles, on the other hand, are those closest to the body, such as those in the shoulders, upper arms, pelvic area, and thighs. Distal myopathies are a group of primary muscle disorders where weakness and atrophy are restricted to distal muscles, at least initially. They are characterised by muscle weakness affecting the ankles and may spread to affect the muscles of the shinbone. Hereditary distal myopathies include Laing myopathy, Miyoshi myopathy, and Distal Myopathy with Vocal Cord and Pharyngeal Signs.
| Characteristics | Values |
|---|---|
| Definition | Distal myopathy is a group of rare progressive genetic disorders that cause weakness and wasting of the muscles in the hands and feet. |
| Symptoms | Muscle weakness and degeneration ranging from mild to severe. Muscles in the hands are affected first, with the legs becoming involved later or not at all. |
| Diagnosis | EMG is an important initial test to confirm the myopathic origin of weakness. MRI and muscle biopsy can also be used for diagnosis. |
| Treatment | DNA testing and dysferlin gene mutation analysis can be used to confirm the presence of distal myopathy. |
| Prevalence | Distal myopathy is rare, with an estimated prevalence of approximately 2 in every 100,000 individuals. |
| Onset | The age of onset varies, but Miyoshi myopathy typically presents before age 20. |
| Progression | The progression of distal myopathy is slow, eventually leading to wheelchair dependency 10 to 20 years after symptom onset. |
| Inheritance | Distal myopathy can be inherited in an autosomal dominant or recessive pattern. |
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What You'll Learn
Distal myopathy gene disorders
Distal myopathies are a group of rare, progressive genetic disorders characterised by muscle weakness and degeneration, typically affecting the hands and feet. The progression of muscle weakness is slow, and muscles in the hands are usually affected first. The age of onset, severity, and progression of symptoms vary greatly, even among individuals in the same family.
The term distal myopathy was first mentioned in 1902, describing a person with concurrent facial weakness, which may have been an early description of myotonic dystrophy type 1. In 1951, distal myopathy was reported in an adult-onset autosomal dominant disorder with weakness of long extensors in the hand, affecting 249 people from 72 Swedish families. The molecular genetic era for distal myopathies began in 1995 with the mapping of Laing’s distal myopathy to chromosome 14 and the discovery of causative MYH7 mutations. The Gene Table of Neuromuscular Disorders now lists 18 gene disorders under the heading of distal myopathies, with seven more recently added.
Distal myopathies are inherited as either autosomal dominant or recessive traits. Dominant genetic disorders occur when only a single copy of an abnormal gene is necessary for the disease to appear. The abnormal gene can be inherited from either parent or can be the result of a new mutation in the affected individual. The risk of passing the abnormal gene from an affected parent to their offspring is 50% for each pregnancy, regardless of the resulting child's sex. Autosomal recessive genetic disorders occur when an individual inherits an abnormal gene for the same trait from each parent. If an individual receives one normal gene and one gene for the disease, they will usually not show symptoms but can still be a carrier.
Some types of distal myopathy include Miyoshi myopathy, Laing's myopathy, Welander distal myopathy, Udd distal myopathy, and distal myopathy with vocal cord and pharyngeal signs (Distal Myopathy 2; MPD2).
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Hereditary distal myopathies
The age of onset varies from early childhood to late adulthood, and the predominant muscle weakness can affect the calf, ankle dorsiflexor, or distal upper limb muscles. A spectrum of muscle pathological changes, varying from nonspecific myopathic changes to rimmed vacuoles to myofibrillar pathology to nuclei centralization, have been noted. Likewise, the underlying molecular defect is heterogeneous. There is also evidence that distal myopathies can result from defective proteins encoded by genes causative of neurogenic disorders, be a manifestation of multisystem proteinopathies, or the result of the altered interplay between different genes.
Some specific types of hereditary distal myopathies include Laing's myopathy, Miyoshi myopathy, GNE myopathy, and Udd's myopathy. Laing's myopathy is an early-onset disorder that begins with selective weakness of foot dorsiflexors and great toe extensors, followed by weakness of neck flexors and finger extensors, and, in some cases, progresses to facial and proximal limb muscle weakness. Miyoshi myopathy is a primary disorder of skeletal muscle that usually presents with onset before the age of 20, early involvement of posterior foreleg muscles, and markedly elevated CK levels. GNE myopathy is a primary skeletal myopathy that usually presents in late adolescence and early adulthood with bilateral foot drop and steppage-pattern gait caused by anterior tibialis muscle weakness. Udd's myopathy is an autosomal dominant disorder first described in Finnish individuals, with all reported cases having a unique 11-bp deletion/insertion that changes four amino acid residues in exon Mex6.
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Distal myopathy diagnosis
Distal myopathy is a class of muscular dystrophies that primarily affect distal muscles, which include the muscles of the lower arms, hands, lower legs, and feet. It is a group of rare, genetic, and degenerative diseases that primarily affect voluntary muscles. Diagnosis of distal myopathy is a multi-step process that involves clinical evaluation, patient history, identification of characteristic findings, and various tests.
One of the key tests for distal myopathy diagnosis is electromyography (EMG), which assesses the health of muscles and the nerves that control them. During an EMG, a needle electrode is inserted through the skin into an affected muscle to record its electrical activity. This test helps determine whether muscle weakness is caused by the muscles themselves or by the nerves controlling them. EMG can also provide clues about the specific type of myopathy, such as myotonic discharges indicating myotonic dystrophy or Pompe's disease.
Blood tests are another important diagnostic tool for distal myopathy. These tests can reveal elevated levels of creatine kinase (CK), an enzyme that is often elevated when muscles are damaged or inflamed. While elevated CK levels can be found in some cases of distal myopathy, they are particularly high in Miyoshi myopathy. However, it is important to note that elevated CK levels alone cannot confirm a distal myopathy diagnosis.
Magnetic resonance imaging (MRI) of muscle tissue is also valuable in distal myopathy diagnosis. MRIs can reveal distinct patterns of muscle damage or involvement, which have been identified in individuals with Welander, Udd, and other distal myopathies. Imaging upper and lower limb muscles with MRI provides valuable insights, especially when the clinical exam is limited, such as in obese individuals.
In some cases, a muscle biopsy may be necessary for distal myopathy diagnosis. A biopsy involves the surgical removal and microscopic examination of affected muscle tissue. It can reveal characteristic changes, such as increased connective tissue, fat, and sub-cellular compartments known as rimmed vacuoles. However, with the availability of next-generation DNA testing, muscle biopsies are not always required, especially if DNA test results are conclusive.
It is important to note that distal myopathies can have similar symptoms to other muscle diseases, such as metabolic myopathies (Pompe disease), inflammatory myopathies (dermatomyositis, polymyositis), and congenital myopathies (nemaline myopathy). Therefore, a thorough differential diagnosis should consider these additional forms of muscle disease.
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Distal limb muscle control
Distal limb muscles refer to the muscles of the hands and feet, fingers and toes. Distal myopathies are a group of rare progressive genetic disorders characterised by muscle weakness and degeneration, which can range from mild to severe. The muscles in the hands are affected first, with the legs becoming involved later, or sometimes not at all. Distal myopathies can lead to clumsiness and an inability to turn the feet and toes upward, making it difficult to pick up the front of the foot when walking.
Distal muscle control can be assessed through an EMG test, which can confirm the myopathic origin of weakness and search for other diagnostic clues. This can include identifying the onset of symptoms, family history and pattern of muscle involvement. MRI scans can also be used to provide valuable insight into patterns of muscle involvement.
Distal muscle control can be improved through robotic rehabilitation, which has been shown to be more effective than proximal-emphasised rehabilitation. This is particularly useful for those recovering from a stroke, with distal-emphasised robotic rehabilitation showing better improvements in muscle strength and quality of movement during functional activities.
The dorsolateral pathways are important for control of distal upper limb movements, while ventromedial pathways act more on the axial and proximal upper limb muscles.
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Distal myopathy treatments
Distal myopathy is a rare, progressive genetic disorder characterised by muscle wasting and weakness. It is a form of muscular dystrophy that specifically involves muscles in the throat, lower legs, forearms, hands, and fingers. While there is currently no cure for distal myopathy, there are treatments available to help manage the condition.
Treatments for Distal Myopathy
Due to the progressive nature of distal myopathy, treatment typically focuses on managing symptoms and slowing the progression of the disease. Here are some common approaches:
- Physiotherapy and Exercise: Physiotherapy and tailored exercise programmes can help improve muscle strength, flexibility, and range of motion. These interventions may include aerobic exercises, strength training, and stretching routines.
- Orthotic Devices: Braces, splints, or other orthotic devices can provide support and improve stability for individuals with distal myopathy. These devices can help with walking, maintaining balance, and performing daily activities.
- Occupational Therapy: Occupational therapy can assist individuals in adapting their environment and learning new ways to perform daily tasks. This may include recommending assistive devices, modifying the home or workplace, and providing guidance on energy conservation techniques.
- Speech Therapy: For those with distal myopathy affecting the throat and vocal cords, speech therapy can be beneficial. A speech therapist can provide exercises to strengthen the vocal cords and improve speech and swallowing abilities.
- Medication: While there is no specific medication to cure distal myopathy, certain drugs may be prescribed to manage associated symptoms. For example, immunosuppressants or corticosteroids may be used to reduce inflammation and slow the progression of the disease.
- Surgical Interventions: In some cases, surgery may be considered to correct deformities or stabilise joints affected by muscle weakness. This can help improve function and mobility, as well as prevent further complications.
- Supportive Care: As distal myopathy can impact an individual's ability to perform daily tasks, supportive care services are important. This may include assistance with activities of daily living, respiratory support, or nutritional guidance to maintain a healthy weight.
- Clinical Trials: Participating in clinical trials can provide access to emerging treatments and therapies. These trials aim to test the safety and effectiveness of potential new treatments, which may offer hope for improved management of distal myopathy in the future.
It is important to note that the treatment plan for distal myopathy should be tailored to the specific needs of each individual, as the symptoms and progression can vary greatly. Working closely with a healthcare team, which may include neurologists, physiotherapists, and occupational therapists, is crucial for effective management of the condition.
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Frequently asked questions
Distal limb muscles are those farther away from the centre of the body, for example, in the hands and feet.
Distal myopathy is a group of disorders that cause weakness and atrophy of distal limb muscles. Miyoshi myopathy, Laing myopathy, and Welander distal myopathy are some examples of distal myopathies.
The symptoms of distal myopathy include muscle weakness and degeneration, which can range from mild to severe. The progression of muscle weakness is slow, typically affecting the hands first and then the legs.
Distal myopathy is typically diagnosed through an EMG test, which confirms the myopathic origin of weakness. Other diagnostic tools include MRI, muscle biopsy, and DNA testing.
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