Myopathies

What are myopathies?

Myopathy is the medical term for muscle disease. Some muscle diseases occur when the immune system attacks the muscles, resulting in undue inflammation known as inflammatory myopathy. This inflammation damages muscle tissue and weakens the muscles.

There are several types of myopathies, which can be hereditary or acquired.

Hereditary myopathies are caused by genetic abnormalities and are rare, being the most common:

• Central body myopathy
• Centronuclear myopathy
• Congenital myopathy due to fiber type disproportion.
• Nemaline myopathy
• Multimininuclear myopathy
• Myotubular myopathy
• Hereditary inclusion body myopathies (HIBM)
• Facioscapulohumeral muscular dystrophy (FSHD)
• Mitochondrial myopathies
• Myotonic dystrophies or syndromes
• Duchenne myopathy
• Becker myopathy

Within acquired myopathies there are certain risk factors, such as autoimmune disorders, endocrine disorders, infections, exposure to toxins, vitamin D deficiency or vitamin A or E toxicity, or some metabolic disorders. The classification of acquired myopathies is more complex, but they can be subdivided into endocrine, inflammatory and toxic myopathies, depending on the cause.

Prognosis of the disease

Myopathies can become severe if not diagnosed and treated in time. Muscle deterioration can cause the patient to stop walking or moving properly. For this reason, early diagnosis and physiotherapy exercises from the onset of the disease are very important.

Symptoms of myopathies

The general symptoms of myopathies include progressive weakening of the muscles and a general loss of strength, even to perform common situations or movements, such as lifting the arms, climbing stairs or getting up from a chair.

Typically, these symptoms occur:

• Loss of muscle tone
• Delayed motor skills
• Facial weakness
• Drooping of the eyelids
• Muscle cramps or twitching

However, symptoms also depend on the type of myopathy:

• Hereditary inclusion body myopathies (HIBM): affect the distal region of the limbs.
• Facioscapulohumeral muscular dystrophy (FSHD): may cause drooping of the eyelids, decreased facial expression, inability to make movements and actions such as whistling.
• Mitochondrial myopathies: may cause ptosis (drooping eyelids).
• Myotonic dystrophies or syndromes: cause delayed muscle relaxation, following contraction of a muscle by a mechanical stimulus.
• Central body myopathy: causes muscle weakness and developmental problems.
• Centronuclear myopathy: although very rare, it can cause muscle weakness in the face, arms, legs and eye muscles, as well as respiratory problems.
• Congenital myopathy due to fiber type disproportion: causes muscle weakness in the neck, face, arms, legs and trunk.
• Nemaline myopathy: this is one of the most frequent and causes muscle weakness in the face, neck, arms and legs, as well as scoliosis. It can also cause feeding and respiratory problems.
• Multimininuclear myopathy: causes severe muscle weakness in the legs and arms, as well as scoliosis.
• Myotubular myopathy: it presents with muscle weakness, flaccidity and respiratory problems.

Medical tests for myopathies

Myopathies can be diagnosed with an accurate neurological examination. During the test, a blood test will be done to analyze muscle enzyme levels, inflammation levels, metabolic rates and hormone levels.

It is also advisable to do an EMG (electromyography), as well as genetic testing and a muscle biopsy to help identify what may be causing the myopathy.

What are the causes of myopathies?

Hereditary myopathies are caused by genetic abnormalities in the chromosomes, some of them on the X chromosome.

In acquired myopathies, the cause will depend on the type of myopathy:

• Endocrine myopathies are usually caused by hormone production in excess or, conversely, in deficiency. The most common is steroid myopathy (steroid excess).
• Toxic myopathies are caused by exposure to certain drugs and/or chemicals, such as cholesterol-lowering drugs, excessive alcohol intake, narcotics, glucocorticoids, herbicides and pesticides….
• Inflammatory myopathies are autoimmune diseases that attack healthy muscle fibers and produce inflammation, damaging the muscle.

Can they be prevented?

There is no way to prevent congenital myopathies. If a woman is at high risk of having a child with a myopathy, genetic testing may be recommended before becoming pregnant.

Treatments for myopathies

Before establishing a treatment, a correct diagnosis is necessary for the best possible outcome. Some of the most common treatments are:

• Corticosteroids. High-dose oral corticosteroids reduce inflammation. Blood muscle enzymes tend to return to normal within 4-6 weeks of starting treatment and many patients regain muscle strength within 2-3 months.
• Combination treatment. The rheumatologist will probably add some other medication to the corticosteroids. This makes it possible to better control the pathology in the long term, in addition to preventing the side effects that corticosteroids can have in the long term (weight gain, redistribution of body fat, thinning of the skin, osteoporosis or cataracts).
• Immune treatments. Patients who suffer from severe myopathies or who do not respond to standard treatments have other options, which are intravenous administration of immunoglobulin, or drugs that inhibit the immune system.
• Physical therapy. Physical therapy can help patients continue to maintain an active lifestyle. In addition, patients who are very weak and do not walk should do range-of-motion exercises to avoid joint contractures and deformities. Patients with medium weakness should do exercises to strengthen muscles. The goal is, in any case, to slowly increase the intensity, so that the patient recovers muscle strength.

Which specialist treats it?

Rheumatologists are the specialists in the diagnosis and treatment of diseases of the muscles, joints and bones. Therefore, they will be the specialists trained to make a correct diagnosis of myopathies.