Myopathy

What is Myopathy?

Myopathy, a term that comes from Greek roots meaning “muscle suffering,” refers to a disease affecting the muscles. The main signs and symptoms of myopathies can include feelings of weakness, stiffness, cramps, and spasms. Myopathies encompass a range of disorders that primarily impact the structure, metabolism, or functioning of our body’s skeletal muscles. Often, these diseases interfere with daily activities due to muscle weakness. Another common symptom of myopathies includes muscle pain. In some individuals, the condition may also be linked to rhabdomyolysis, a serious syndrome where muscle tissue breakdown occurs.

What Causes Myopathy?

Myopathies, or muscle diseases, can often be caused by a disruption in the muscle’s structure or the metabolic balance within the muscle. This can be due to inherited genetic diseases, defects in metabolism, certain drugs and toxins, bacterial or viral infections, inflammation, or irregularities in minerals, hormones, and electrolytes.

There are many types of inherited myopathies. Some are caused by mitochondrial problems, like the Mitochondrial Myopathies which include MELAS (causing symptoms like stroke and lactic acidosis), or the Kearns-Sayre syndrome. Several other types are also under mitochondrial myopathies like Leigh syndrome, Leber hereditary optic neuropathy, etc. Congenital Myopathies include Nemaline Myopathy, Core Myopathy, Centronuclear Myopathies. Metabolic myopathies are associated with energy production in muscles and can include lipid myopathies and glycogen storage diseases like Pompe, Cori, and McArdle diseases. Channelopathies cause issues with the electrical signals in the muscles leading to conditions like periodic paralysis and paramyotonia congenita among others.

Muscular Dystrophies are a large group of inherited myopathies. This group includes Dystrophinopathies like Duchenne and Becker muscular dystrophies; the Myotonic muscular dystrophies (Type 1 and Type 2); Facioscapulohumeral muscular dystrophies; Emery-Dreifuss muscular dystrophy, among others.

In addition to inherited muscle diseases, acquired myopathies can occur from exposure to certain toxins or due to conditions like bacterial or viral infections. Toxic Myopathies include necrotizing myopathies causes by drugs like statins, labetalol, propofol, or alcohol, etc. Mitochondrial myopathies can also be caused by some antiretrovirals, and there are several more categories under this. Inflammatory Myopathies are often immune-mediated causing conditions such as Dermatomyositis, Inclusion Body Myopathy, among others. Infectious Myopathies could be due to bacteria, viruses, and parasites.

Furthermore, Endocrine Myopathies are caused by conditions affecting the thyroid, parathyroid, adrenal glands or due to diabetes leading to conditions like hyperthyroidism, hypothyroidism, Addison’s disease, among others. Hypo- and hyperkalemia (low or high potassium levels), hypercalcemia (elevated calcium), and other electrolyte imbalances are also causes for Myopathies.

Please note: Rhabdomyolysis, a condition in which muscle tissue breaks down, often causing kidney damage, is not considered a primary myopathy. This can occur with or without another muscle disease at play.

Risk Factors and Frequency for Myopathy

Inflammatory and endocrine myopathies are a common kind of muscle disease, typically seen in middle-aged women more often than men. The occurrence (incidence) rate of these types of muscle disease varies from 1.16 to 19 cases per million people each year, whereas the total cases (prevalence) ranges from 2.4 to 33.8 cases per 100,000 people.

Dystrophinopathies are the most frequently inherited muscle diseases, predominantly affecting males. However, both genders across all races and ethnicities can be affected. Duchenne’s and Becker’s muscular dystrophies are the most common cases amongst these, with an occurrence rate between 19.8 and 25.1 cases per 100,000 people each year. Mitochondrial myopathies affect about 1 in 4300 people. However, other types of inherited muscle diseases are rare.

• Inflammatory and endocrine myopathies are usually found in middle-aged women more than men.
• The incidence rate per year varies from 1.16 to 19 cases per million people.
• The prevalence ranges from 2.4 to 33.8 cases per 100,000 people.
• Dystrophinopathies are the most common inherited muscle disease, mostly affecting males.
• Among these, Duchenne’s and Becker’s muscular dystrophies occur between 19.8 and 25.1 times per 100,000 people annually.
• Mitochondrial myopathies affect about 1 in 4300 people.
• Other forms of inherited muscle disease are rare.

Signs and Symptoms of Myopathy

Myopathies are conditions that primarily lead to muscle weakness, not affecting our senses. These ailments are usually detected when patients exhibit difficulty with tasks like standing up from a seating position, climbing stairs, or raising their arms above their heads. Key signs include weakness in muscles near the pelvis or shoulder, with those near the pelvis being most frequently affected. However, some myopathies show up in other areas such as the thighs, back muscles, or fingers. Other symptoms could include muscle pain, skin rashes, fatigue, cramps, and even dark urine, the latter being a marker of kidney damage specifically in the case of a condition called rhabdomyolysis.

There are many types of myopathies, for instance, polymyositis and dermatomyositis are both known to impact women more than men and primarily cause weakness in muscles near the pelvis region. Polymyositis often involves joint pain, while dermatomyositis usually comes with a range of symptoms, most notably skin rashes of varying types.

• Heliotrope rash – A purple rash present on the eyelids
• Gottron’s papules – A reddish, lumpy rash found on the back of the fingers
• Shawl sign – A reddish rash that shows up on the shoulders and back

While other complications may include lung disease, gastrointestinal vasculitis, and paraneoplastic syndrome which is associated with underneath cancer.

Myopathies can also be associated with thyroid disease, whether it’s hypo- (low) or hyper- (high) thyroid activity. Both these conditions manifest as muscle weakness and peripheral neuropathy (a condition that affects the nerves). Depending on whether the myopathy is linked to hypo- or hyperthyroid disease, it might be associated with other specific symptoms.

Many other acquired myopathies exist, each with its own set of symptoms, like sarcoidosis myopathy, amyloid myopathy, and critical illness myopathy. This grouping also includes inheritable conditions like Duchenne muscular dystrophy, myotonic dystrophy, mitochondrial myopathies, and glycogen storage diseases. These hereditary conditions typically affect children and are quite rare. They can have severe complications and often impact the life expectancy of the patient, depending on the severity of the illness.

Testing for Myopathy

Your doctor may need to conduct a set of tests if they suspect you have a condition related to your muscles. Here’s a run-through of what those tests may include:

1) Lab tests:

These may include a complete blood count, tests checking for levels of certain chemicals in your blood such as blood urea nitrogen, serum creatinine, different electrolytes, and some enzymes. Doctors may also look for markers of inflammation in the body and test thyroid function, since an underactive or overactive thyroid can sometimes cause muscle problems. They also may test for certain antibodies that can indicate specific conditions, such as dermatomyositis or immune-mediated necrotizing myopathy. A urine test can check for the presence of a protein called myoglobin which may indicate muscle damage.

2) Electromyography (EMG) and Nerve Conduction Study (NCS):

This involves using small needles to test the electrical activity in your muscles and nerves. It can help determine whether the issue lies in your muscles or nerves, assess the severity of your condition, and guide the choice for a muscle biopsy site. Certain findings during this test can point to certain kinds of muscle conditions. However, sometimes this test might be skipped if you have very clear symptoms, high levels of a muscle enzyme called creatine kinase in your blood, or a family history that strongly suggests a muscle condition.

3) Electrocardiography (ECG):

This test can help identify issues like hypokalemia (low potassium levels), which can affect your heart’s function. Manifestations may include nonspecific changes in the ST and T portions of the ECG, a long PR interval, U waves, or a wide QRS complex.

4) Muscle biopsy:

This procedure involves taking a small piece of muscle tissue to be examined under a microscope. The pathologist will look for certain patterns and features which could give clues to what the underlying cause might be.

5) Muscle MRI:

This test uses magnetic fields and radio waves to create images of your muscles. It can help spot muscle damage, inflammation, or fatty tissue replacing muscle tissue – a sign of chronic muscle damage. The MRI can also guide the choice of a biopsy site and is particularly useful in children, since it’s less invasive.

Treatment Options for Myopathy

Myopathy refers to diseases that cause muscle weakness because of a problem with the muscle itself. Treatment for myopathy primarily involves different therapies – like exercises, physical and occupational therapies – and changes in nutrition and diet. Some genetic diseases may require testing and counseling.

When it comes to inherited muscle diseases known as muscular dystrophies, medication like prednisone is often used. Prednisone improves muscle strength, helps muscles grow, and slows down the progression of the disease. For a specific type of inherited myopathy known as mitochondrial myopathies, creatine monohydrate is typically used to help relieve symptoms. Although Coenzyme Q10 is sometimes used, more research is needed to confirm its effectiveness.

Acquired myopathies, which are muscle diseases that develop later in life rather than from birth, typically get better if we address the original disease which caused it. This cause could be something like a thyroid disease or a disease known as sarcoidosis. Some muscle diseases are caused by infections – whether bacterial, viral, fungal, parasitic, or spirochetes – and these generally get better when the infection is treated. Likewise, if the muscle disease is caused by a certain drug or toxin, treatment usually involves removing the offending substance and avoiding it in the future. For muscle disease related to HIV, antiretroviral therapy and possibly steroids are typically used.

For what are called “inflammatory myopathies” and autoimmune-related muscle diseases, treatment generally involves drugs that affect the immune system, as well as steroids, to fight inflammation and manage symptoms. While steroids generally work better and have fewer side effects, treatments can also involve methotrexate, azathioprine, cyclosporin, and cyclophosphamide. Some severe cases, however, do not respond well to these medications and continue to cause muscle weakness in the patient.

Rhabdomyolysis is a serious and potentially life-threatening condition that can result from muscle damage. Its treatment’s main aim is to prevent kidney damage by removing the harmful substances released from the damaged muscles. This is done by administering a high volume of intravenous fluids and by carefully monitoring both kidney function and electrolyte balance.

What else can Myopathy be?

The differential diagnosis for myopathy is broad and can vary depending on the associated symptoms. Various conditions can mimic myopathy:

• Guillain-Barre Syndrome: This condition typically develops after a mild respiratory or gastrointestinal illness and involves finger numbness and muscle weakness starting in the lower body and can spread to the arms, trunk, cranial nerves, and respiratory muscles.
• Tick-borne diseases: These diseases are typically confirmed through a blood test known as the indirect immunofluorescence antibody (IFA) assay.
• Lambert-Eaton Myasthenic Syndrome (LEMS): This condition is marked by muscle weakness, reduced tendon reflexes, changes after muscle contraction, and changes in the nervous system due to a decrease in the release of a chemical responsible for transmitting signals in the nervous system called acetylcholine.
• Myasthenia gravis: This is an autoimmune disorder where the body’s immune system targets the receptors in the muscle-nerve junction, causing weakness and fatigue in the muscles. The frequently used muscles, especially those that control swallowing and facial movements, are commonly affected.

Other conditions that may cause symptoms similar to myopathy include:

• Malignant Hyperthermia: A severe reaction to certain medications used during general anesthesia.
• Myotonia: Impaired muscle relaxation after contraction.
• Myositis Ossificans: An abnormal bone tissue growth within a muscle.
• Myositis associated with vasculitis: Inflammation of the blood vessels leading to muscle inflammation.
• Paraneoplastic syndromes: These are rare disorders triggered by an altered immune system response to a cancerous tumor known as a neoplasm.
• Direct trauma or excessive exercise: These can cause direct damage to the muscle.
• Nutritional deficiencies: Insufficient intake of certain nutrients, such as vitamin E, or conditions that inhibit nutrient absorption can also lead to myopathy.

What to expect with Myopathy

The main aim of treatment for most muscle diseases (known as myopathies) is to slow down or halt the progression of the disease. This is particularly the case for inherited, metabolic, and inflammatory myopathies. Some complications linked with inherited myopathies can even be life-threatening. The overall health and well-being of those living with these types of myopathies often tend to suffer.

However, for acquired myopathies (ones that are not inherited but happen later in life), how well a person recovers really depends on what caused it. This could be anything from how severe the overall health condition is, the type of infection involved, or the damage caused by medication or harmful substances. The best way to manage these types of muscle diseases is generally to treat the main health condition that caused them.

Possible Complications When Diagnosed with Myopathy

The issues that come up from different types of muscle diseases, or myopathies, largely have to do with how the disease progresses. Certain types, like ones that you are born with, metabolic ones, or ones that are passed down through families, can lead to severe complications. These might include diseases that affect the shape of your heart, infections that keep coming back, and dangerous body-wide infections known as sepsis. It could also lead to neuropathies which are nerve diseases, failing lungs, or kidneys that no longer work.

In contrast, the problems that arise from acquired myopathies will typically depend on what caused the disease. For example, if it was due to an infection, then the complications depend on the type of infection. Or if it was due to a drug or toxin, the complications depend on how much of the substance was present and for how long.

Here is a list of possible complications:

• Death
• Rhabdomyolysis (a condition where muscle fibers die and release a harmful protein into the bloodstream)
• Heart rhythm problems
• Paraneoplastic syndromes (a group of rare disorders triggered by an altered immune system response to a cancer)
• Heart failure
• High blood pressure (Hypertension)
• Renal failure (when kidneys stop working)
• Neuropathies, including seizures and abnormal development of the brain
• Difficulty with movement
• Bedsores
• Infections and sepsis
• Irreversible wasting of muscles
• Repeated problems swallowing (Recurrent dysphagia)
• Severe stomach dilation
• Failure of the respiratory system
• Endocrinopathies (disorders of the glands that make hormones)
• Cataracts (clouding of the lens of the eye)
• Sensorineural hearing loss (a type of hearing loss where the root cause lies in the inner ear, most commonly from damage to the hair cells in the cochlea)

Preventing Myopathy

Some muscle-related diseases are long-term and may require you to change your lifestyle. A key factor in managing these conditions is maintaining a well-rounded diet filled with a variety of fruits and veggies. Apart from good nutrition, staying physically active is crucial. You’ll often be advised to engage in physical therapy and moderate exercise routines. This advice is particularly important for individuals struggling with metabolic muscle diseases like lysosomal storage disease and glycogen storage disease. In addition to following a balanced diet and planned exercises, these patients are urged to reduce diet components that could trigger their condition.

Inflammatory muscle diseases are also persistent. Patients found to have such conditions usually improve by keeping up with a regular exercise routine alongside their medical treatments. Monitoring the progress of the disease and the severity of your symptoms is also important, along with staying on top of your medical check-ups. There are inherited muscle diseases that often come with additional health complications. Therefore, it’s essential to anticipate health complications to increase survival rates and to seek immediate medical attention in case of emergencies, such as heart muscle diseases or widespread infections.