Content

Introduction

The myopathies they are diseases that damage the voluntary muscles, also called striated muscles, which contract at the will of the subject; in the most severe forms, the heart muscle may also be involved (also striated but not voluntary).

There are various types of myopathies, grouped into two large families:

  • hereditary myopathies, include muscular dystrophies, congenital myopathies, metabolic myopathies and muscle channelopathies
  • acquired myopathies or secondary, include inflammatory myopathies, myopathies associated with endocrine system disorders, intoxications or the intake of certain drugs

The main disorder (symptom) of a myopathy is a decrease in muscle strength (weakness), due to the alteration of muscle fibers; the weakness can be localized or generalized, fluctuating, stable or progressive (up to the reduction of muscle mass), depending on the type of myopathy.

Each myopathy must be ascertained (diagnosed) and treated specifically; the severity of symptoms depends on the type of myopathy and the "age at onset". A hereditary myopathy that occurs in childhood is often degenerative, for example Duchenne muscular dystrophy, which affects males from 2-4 years of age causing weakening of the skeletal muscles. Becker's muscular dystrophy, on the other hand, has onset in adolescence and is less disabling. Among the acquired muscular diseases, inflammatory myopathies are the most frequent and can occur at any age.

Symptoms

  • muscle fatigue: it is the most common disorder, it can affect some specific muscles or, in severe cases, all the muscles of the body
  • feeling tired
  • exercise intolerance
  • muscle aches (myalgia)
  • contractures and muscle stiffening
  • strength deficit
  • reduction in muscle mass

In severe neonatal forms (hereditary myopathies) the muscular disorders are generally more marked and can also affect the muscles involved in breathing and the heart muscle; other manifestations may be the loss of muscle mass and joint contractures.

Causes

There are many causes that lead to the onset of a myopathy.

Muscular dystrophies are caused by structural changes (mutations) in genes that are important for maintaining muscle structure. Children with Duchenne muscular dystrophy have an almost total deficiency of a muscle protein, dystrophin; in boys with Becker muscular dystrophy, dystrophin does not work properly or its quantity is insufficient.

Congenital myopathies with onset at birth, more rarely in adulthood, are also caused by mutations in several genes that cause the malfunction or loss of structural proteins of the muscle. Muscle channelopathies are caused by genetic mutations that alter ion channels muscle causing reduction or increase in the excitability of muscle cells.

Hereditary metabolic myopathies are caused by genetic mutations that determine defects or deficiencies in the enzymes that transform certain substances (eg sugars, fats) to produce energy, with consequent accumulation of the same.

The causes of inflammatory myopathies, such as dermatomyositis (which also affects the skin), polymyositis and inclusion body myositis, have been attributed to a malfunction of the immune system, normally responsible for defending the body from infectious agents (viruses, bacteria , etc.).Similarly to what happens in autoimmune diseases (rheumatoid arthritis, systemic lupus erythematosus), in inflammatory myopathies the immune system mistakenly attacks and damages the muscle cells.

In acquired metabolic myopathies, the biochemical muscle defect is due to dysfunctions of the endocrine or hormonal system (for example, diseases of glands such as the thyroid or pituitary gland), to factors of an external nature, such as intoxication from alcohol, heroin, amphetamines, or all " taking medications such as cortisone or statins.

Diagnosis

Given the variety and heterogeneity of the different forms of myopathy, the physician must carefully evaluate the patient's clinical and family history and the presence of typical symptoms.

In general, to ascertain myopathies, the following are necessary:

  • neurological visit accurate
  • blood tests, dosage of muscle enzymes, such as creatine kinase (CK) and lactic dehydrogenase (LDH) which are indices of muscle fiber damage, and of some metabolites, such as lactic acid, produced during muscle contraction; inflammatory parameters (ESR, C reactive protein, immunoglobulins)
  • electromyography: is an examination that involves the insertion of a needle electrode into the muscle to measure its electrical activity; serves to detect the presence of alterations in muscle fibers
  • muscle biopsy, or the removal of a small portion of muscle which is then analyzed under a microscope or with biochemical tests; allows to highlight and quantify tissue damage. It is the most important diagnostic test that allows a differential diagnosis between the various forms of myopathies
  • genetic tests to identify any genes responsible for hereditary myopathies

For some years it has also been possible to do one muscle magnetic resonance, with which you can get even more accurate results.The examination is very useful both for assessing the extent of muscle damage and for checking the effectiveness of the therapy over time.

Thanks to the contribution of the Telethon Foundation and the Italian Union for the Fight against Muscular Dystrophy (UILDM), in 2021 the first national register of patients with muscular dystrophies and congenital myopathies was created (http://www.registronmd.it). The registry aims to collect personal, genetic and clinical data that can be used to increase knowledge of these diseases, improve diagnosis and assistance, and accelerate the discovery of new therapies.

Therapy

A definitive treatment for the various forms of myopathies, in particular the degenerative forms with early onset, does not exist to date. However, with specific therapies in many cases the disorders (symptoms) can be effectively controlled.

Treatment varies according to the type of myopathy. Physiotherapy is used to improve muscle strength, decrease muscle stiffness and pain, and counteract the osteo-tendon retractions of the various joint districts. For muscular dystrophies, particularly Duchenne muscular dystrophy, it is important that a multidisciplinary approach is used, including pharmacology, physiotherapy, orthopedic surgery, cardiac monitoring and respiratory assistance, in order to reduce symptoms. and improve life expectancy and quality of life.

In the case of acquired myopathy, therapy is aimed at eliminating the cause. In inflammatory myopathies, high-dose steroids (cortisone) are the first choice drugs; immunosuppressive drugs can be combined with or replace steroid therapy. In case of myopathy due to dysfunction of the endocrine system, the basic hormonal defect must be corrected.

Genetic counseling is recommended in the case of a diagnosis of hereditary myopathy.

Prevention

With the exception of secondary myopathies due to intoxication from substances of abuse or drugs, there is no real prevention of these diseases as the cause is often of genetic origin.

Living with

Hereditary and acquired myopathies, whether they occur from birth or arise in adulthood, are disabling diseases to a greater or lesser extent depending on the subgroup to which they belong, the anatomical part affected and the severity of the damage.

Muscular dystrophies are the most disabling forms; they are classified as degenerative myopathies and generally produce severe disability. In these cases, in addition to following the most effective medical therapy, it is necessary to be constantly assisted by rehabilitation specialists. It may be appropriate to resort to psychological counseling, which is useful to provide both emotional and practical support to the family of the person with myopathy.

Less disabling are congenital non-dystrophic myopathies and metabolic, inflammatory and toxic myopathies; the latter, if treated promptly with adequate drugs and therapies, often regress.

In-depth link

Italian Union for the fight against muscular dystrophy (UILDM). Dystrophinopathies: Duchenne and Becker

Italian Union for the fight against muscular dystrophy (UILDM). Inflammatory myopathies

Italian Union for the fight against muscular dystrophy (UILDM). Congenital myopathies

Italian Union for the fight against muscular dystrophy (UILDM). Metabolic myopathies

Registry of patients with neuromuscular diseases

Cliveland Clinic Center for Continuing Education. Myopathy

Paganoni S, Amato A. Electrodiagnostic Evaluation of Myopathies. Physical Medicine and Rehabilitation Clinics of North America. 2013; 24: 193-207  

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