Maximus Gage
Proximal limb muscles are those closest to the centre of the body, including the muscles of the shoulders, upper arms, pelvic area, and thighs. Proximal myopathy is a condition that causes symmetrical weakness of the proximal upper and/or lower limbs. This can be caused by a variety of factors, including drugs, alcohol, thyroid disease, osteomalacia, idiopathic inflammatory myopathies, hereditary myopathies, malignancy, infections, and sarcoidosis. Limb-girdle muscular dystrophy (LGMD) is a group of disorders characterised by weakness and atrophy of the proximal limb muscles, specifically around the hips and shoulders. LGMD can cause a range of symptoms, including an unusual walking gait, difficulty with daily activities, and in some cases, breathing problems and cardiomyopathy.
| Characteristics | Values |
|---|---|
| Definition | Proximal limb muscles are those closest to the centre of the body. |
| Location | Hips, shoulders, upper arms, pelvic area, and thighs. |
| Associated Conditions | Limb-girdle muscular dystrophy (LGMD), inflammatory myopathies, endocrine myopathies, colchicine-induced myopathy, hypothyroid myopathy, and more. |
| Symptoms | Muscle weakness, atrophy (wasting), pain, and cramping. |
| Diagnosis | Creatine kinase, thyroid function, vitamin D levels, neurophysiological studies, muscle imaging, and muscle biopsy. |
| Treatment | Removal of offending agents, correction of endocrine/metabolic problems, corticosteroids, immunosuppressive therapy, physical therapy, rehabilitation, and genetic counselling. |
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What You'll Learn
Proximal myopathy causes and symptoms
Proximal myopathy is a condition characterised by symmetric weakness affecting the proximal muscles of the limbs. The proximal muscles control the shoulder blade (scapula), and weakness in these muscles can result in a "winging" appearance. Proximal myopathy can present in both the upper and lower limbs, causing generalised weakness and muscle pain that can significantly impact an individual's daily life.
There are various causes of proximal myopathy, including drugs, alcohol, thyroid disease, osteomalacia, endocrine disorders, and hereditary factors. In terms of drugs, colchicine therapy can induce myopathy as a rare side effect, and steroid-induced myopathy is also recognised, particularly with oral and intravenous formulations. Proximal myopathy can also be caused by sodium-glucose co-transporter 2 (SGLT2) inhibitors, a class of antidiabetic drugs.
Hereditary proximal myopathies include Duchenne's and Becker's muscular dystrophies, which are the most prevalent forms, as well as limb girdle muscular dystrophies, facioscapulohumeral muscular dystrophy, and proximal myotonic myopathy. Additionally, glycogen and lipid storage diseases can contribute to proximal myopathy. For example, McArdle's disease, a glycogen storage disease, can cause fast exhaustion, myalgia, and cramping in working muscles.
Proximal myopathy can also be associated with inflammatory conditions such as polymyositis, dermatomyositis, inclusion body myositis (IBM), and Systemic Lupus Erythematosus (SLE). Overlap syndromes, where inflammatory rheumatic disorders present with clinical signs of multiple immunological diseases, can also lead to proximal myopathy. Furthermore, endocrine disorders such as Conn's syndrome and hypothyroidism have been implicated in causing proximal myopathy.
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Proximal myopathy diagnosis
Proximal myopathy is a condition that causes muscle weakness and pain, affecting the proximal muscles of the limbs, which control movement in areas such as the shoulder blade. The condition can be challenging to diagnose due to its varied presentation. The most common pattern is symmetric weakness, which can affect the upper and/or lower limbs.
The first step in diagnosing proximal myopathy is to identify the underlying cause, which can include a broad range of factors such as drugs, alcohol, thyroid disease, osteomalacia, endocrine disorders, toxins, malignancy, infections, sarcoidosis, and hereditary myopathies. Initial tests can include creatine kinase, thyroid function, and vitamin D levels. Further evaluation may involve neurophysiological studies, muscle imaging, and muscle biopsy, particularly if no toxic, metabolic, or endocrine cause is identified.
In terms of specific diagnostic approaches, it is important to distinguish proximal myopathy from other conditions with similar presentations, such as other muscle disorders or rheumatologic diseases. Reflexes are usually intact in proximal myopathy, so any abnormal reflexes may suggest a neurological cause. A comprehensive neurological examination should be conducted, including an examination of the face, hands, lower limbs, chest, and abdomen, as any abnormalities can aid in differential diagnosis.
Proximal myopathy can be associated with inflammatory myopathies, which have an incidence rate of 1.16 to 19 per million people per year. It is also linked to hereditary disorders, such as limb girdle muscular dystrophies, facioscapulohumeral muscular dystrophy, and Duchenne and Becker muscular dystrophy. In terms of treatment, management depends on the underlying cause but can include removing the offending agent, correcting endocrine or metabolic problems, corticosteroids, immunosuppressive therapy, and physical therapy.
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Proximal myopathy management and treatment
Proximal myopathy is a condition characterised by symmetrical weakness of the proximal upper and/or lower limbs. The proximal muscles are those closest to the centre of the body, including the muscles in the shoulders, upper arms, hips, and thighs. This condition can cause significant difficulty in performing daily activities such as bathing, dressing, or even simple tasks like combing one's hair. Proximal myopathy can result from a broad range of underlying causes, including drug use, alcohol consumption, thyroid disease, osteomalacia, idiopathic inflammatory myopathies, hereditary myopathies, malignancy, infections, and sarcoidosis.
The management and treatment of proximal myopathy depend on the specific underlying cause. Here are some common approaches:
Initial Evaluation and Diagnosis
Simple tests, such as creatine kinase, thyroid function, and (25)OH vitamin D levels, are typically the first step in evaluating proximal myopathy. If no toxic, metabolic, or endocrine cause is identified, further evaluation may be necessary, including neurophysiological studies, muscle imaging, and muscle biopsy.
Removal of Offending Agents
In many cases, proximal myopathy is caused by exposure to toxins or certain medications. Discontinuing the use of offending agents, such as alcohol, toluene, or specific medications like statins or glucocorticoids, can lead to significant improvement in symptoms.
Treating Underlying Conditions
For endocrine and metabolic disorders, addressing the underlying condition can help manage proximal myopathy. For example, treating thyroid disorders, adrenal dysfunction, parathyroid issues, or pituitary gland disorders can alleviate muscle weakness associated with these conditions.
Therapy and Rehabilitation
Physical therapy and rehabilitation play a crucial role in managing proximal myopathy, especially in cases of congenital myopathy or muscular dystrophy. These therapies can help improve strength, muscle bulk, and slow the progression of the disease.
Immunosuppressive Therapy and Corticosteroids
For cases of idiopathic inflammatory myopathies (IIM), immunosuppressive therapy and corticosteroids are often used to manage the condition. Corticosteroids are also the conventional treatment for sarcoidosis, an inflammatory disease sometimes associated with proximal myopathy.
Genetic Counselling
Genetic counselling is recommended for all patients with inherited myopathy and their family members. This counselling can help identify potential hereditary causes and provide guidance for the future.
It is important to note that most inherited and genetic myopathies do not have a specific cure, and management focuses on symptom control and various forms of therapy. However, specific medications can treat certain disorders, such as Duchenne muscular dystrophy and Pompe disease.
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Limb girdle muscular dystrophy (LGMD)
Proximal muscles are those closest to the centre of the body; distal muscles are farther away from the centre, for example, in the hands and feet. Proximal myopathy presents as symmetrical weakness of the proximal upper and/or lower limbs.
Limb-girdle muscular dystrophy (LGMD) is a group of disorders with many subtypes categorized by disease gene and inheritance. LGMD usually manifests in the proximal muscles around the hips and shoulders. The shoulder girdle is the bony structure that surrounds the shoulder area, and the pelvic girdle is the bony structure surrounding the hips. Collectively, these are called the limb girdles, and it is the observed weakness and atrophy (wasting) of the muscles connected to the limb girdles that has given this group of disorders its name. LGMD is the fourth most common muscular dystrophy, after the dystrophinopathies, myotonic dystrophies, and facioscapulohumeral muscular dystrophy.
The prevalence of LGMD, as a group, likely ranges from 2.27 to 10 per 100,000 (1:44,000 to 1:10,000). The prevalence of individual LGMDs, as studied in the United States, in descending order, are those due to mutation of 1) calpain, 2) dysferlin, 3) collagen VI, 4) sarcoglycans, 5) anoctamin 5, and 6) fukutin-related protein. In Euroasia, CAPN3 mutations are the most common cause of LGMD, however, in northern Europe, mutations in FKRP are also very common. It is difficult to calculate the worldwide prevalence of even the most common LGMD types due to the founder effect causing varying prevalence by region. The less common types are very rare, often only described in limited regions of the world.
The various forms of LGMD are caused by mutations in many different genes. These genes provide instructions for making proteins that are involved in muscle maintenance and repair. Some of the proteins produced from these genes assemble with other proteins into larger protein complexes. These complexes maintain the physical integrity of muscle tissue and allow the muscles to contract. Other proteins participate in cell signalling, cell membrane repair, or the removal of potentially toxic wastes from muscle cells. LGMD type 1 includes forms of the disorder that have an inheritance pattern called autosomal dominant. LGMD type 2 includes forms of the disorder that have an inheritance pattern called autosomal recessive. Calpainopathy, or limb-girdle muscular dystrophy type 2A, is caused by mutations in the CAPN3 gene. Type 2A is the most common form of limb-girdle muscular dystrophy, accounting for about 30 per cent of cases. Dysferlinopathy, also called limb-girdle muscular dystrophy type 2B, is caused by mutations in the DYSF gene. Sarcoglycanopathies are forms of limb-girdle muscular dystrophy caused by mutations in the SGCA, SGCB, SGCG, and SGCD genes. These sarcoglycanopathies are known as limb-girdle muscular dystrophy types 2D, 2E, 2C, and 2F, respectively.
There is currently no known cure or treatment for LGMD. However, MDA-supported scientists are pursuing several strategies in muscular dystrophy research that have implications for LGMD, including gene therapy, exon skipping, stop codon read-through, and myostatin blocking. Physical therapy may be required to maintain as much muscle strength and joint flexibility as possible. Corticosteroids in LGMD 2C-F individuals show some improvement.
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Duchenne and Becker muscular dystrophy
Proximal myopathy is characterised by symmetrical weakness of the proximal upper and/or lower limbs. It can be caused by a range of factors, including drugs, alcohol, thyroid disease, and infections. Hereditary myopathies, such as limb girdle muscular dystrophy and facioscapulohumeral muscular dystrophy, are also a cause of proximal myopathy.
Duchenne and Becker muscular dystrophies are two related conditions that are forms of hereditary proximal myopathies. They primarily affect skeletal muscles, which are used for movement, and heart (cardiac) muscle. These conditions occur almost exclusively in males, with Duchenne muscular dystrophy being one of the most common inherited disorders worldwide.
Duchenne muscular dystrophy is characterised by progressive muscle degeneration and weakness due to alterations in a protein called dystrophin, which helps keep muscle cells intact. The absence of this protein in muscle cells makes them fragile and easily damaged. Boys with Duchenne muscular dystrophy may experience muscle weakness from early childhood, which worsens rapidly. They may have delayed motor skills and frequent falls, and their calves may be unusually large. By adolescence, they are usually dependent on wheelchairs. The condition also leads to a weakening of the heart and respiratory muscles, making it a fatal disorder that requires careful medical management.
Becker muscular dystrophy is similar to Duchenne muscular dystrophy but typically has a later onset, usually in the teens or early adulthood, and progresses at a slower rate. It is caused by a mutation in the same gene as Duchenne muscular dystrophy, but the signs and symptoms are usually milder and more varied. While muscle weakness may appear later in childhood or adolescence, it worsens slowly over time. Becker muscular dystrophy can also lead to heart problems, with the cardiac muscle becoming enlarged and developing into dilated cardiomyopathy, which can cause an irregular heartbeat, shortness of breath, fatigue, and swelling of the legs and feet.
Both Duchenne and Becker muscular dystrophies are caused by mutations in the DMD gene, which provides instructions for making dystrophin. These mutations alter the structure or function of dystrophin or prevent any functional dystrophin from being produced. In Duchenne muscular dystrophy, there is a complete absence of functioning dystrophin in the muscles, while in Becker muscular dystrophy, some dystrophin is present but not enough for normal muscle function. These mutations can be detected by a genetic blood test.
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Frequently asked questions
Proximal limb muscles are those closest to the centre of the body, as opposed to distal muscles, which are farther away from the body's centre, for example, in the hands and feet.
Proximal myopathy is a condition that presents as symmetrical weakness of the proximal upper and/or lower limbs. It can be caused by a variety of factors, including drugs, alcohol, thyroid disease, osteomalacia, and infectious agents.
Symptoms of proximal myopathy include generalized weakness and muscle pain, which can disturb everyday life. In some cases, patients may experience progressive muscle weakness, weight loss, and difficulty with activities such as walking, climbing stairs, and performing overhead tasks.
