Metabolic myopathy

Metabolic myopathy
Metabolic myopathy is a whole complex of diseases caused by a lack of enzymes or metabolic disorders in muscle tissue. These diseases are characterized by symptoms such as muscle weakness, cramps, pain, paresis and others. A neurologist usually makes a diagnosis based on patient complaints, muscle biopsies, and laboratory tests.

The content of the article:
Causes of metabolic myopathies
Classification of metabolic myopathies
Symptoms of metabolic myopathy
Diagnosis of metabolic myopathies
Treatment of metabolic myopathies
Prognosis and prevention of metabolic myopathies
Metabolic myopathy
Treatment of pathologies should be comprehensive and include vitamin therapy, diet therapy, orthopedic correction, medication.

The group of metabolic myopathies includes many congenital and acquired diseases that occur in both children and adults. Statistical studies prove that metabolic myopathies develop in five cases out of a thousand. The prognosis for adult patients with an acquired form of pathology is more favorable than for patients with a congenital form. As for children, for them, in most cases, the prognosis of the disease is unfavorable.

Causes of metabolic myopathies
Metabolic myopathies can be both congenital and acquired. As for acquired diseases, they are in most cases provoked by endocrine pathologies: hypothyroidism, hyperthyroidism, Cushing’s and Addison’s diseases, hyperaldosteronism, acromegaly. The cause of the disease may also be chronic intoxication of the body due to alcohol abuse or iatrogenic effects. In some cases, metabolic myopathies occur due to chronic liver diseases (liver failure, kidney (chronic renal failure, uremia, electrolyte disorders) and the cardiovascular system.

The main cause of congenital diseases in neurology is considered hereditary predisposition. The transmission of the damaged gene in most cases is carried out autosomal recessive, in rare cases – on the maternal side. Sporadic and random gene mutations have also been recorded in the practice of neurologists. Congenital myopathies are caused by pathologies of the ion channels of muscle membranes and a violation of the normal functioning of mitochondria.

Classification of metabolic myopathies
In neurology, primary (congenital) and secondary (acquired) forms of the disease are distinguished. Secondary metabolic myopathies are a consequence of serious health disorders, especially endocrine diseases. Primary disorders of the metabolism of muscle tissue are divided into several varieties, depending on the reasons that caused their appearance.

The group of diseases caused by impaired glycogen metabolism includes pathologies such as Andersen’s disease, Pompe disease, Corey-Forbes disease, FGC deficiency, McArdle’s disease, LDH deficiency, Tauri disease, phosphoglyceromutase deficiency, phosphorylase b kinase deficiency. Caused by a violation of lipid metabolism — acetyl-CoA dehydrogenase deficiency, carnitine deficiency, CBT deficiency. In case of a violation of purine metabolism, the patient is diagnosed with a deficiency of the enzyme MADA. There is also a group of mitochondrial myopathies, which includes cytochrome b, b 1, reductase enzyme deficiency, and ATP deficiency.

Symptoms of metabolic myopathy
The clinical picture of metabolic myopathy is characterized by extensive symptoms. However, they can be grouped depending on what disorders in the body caused the disease. In neurology, glucose and glycogen metabolism disorders, mitochondrial myopathies and lipid metabolism disorders are distinguished.

Mitochondrial myopathies
Mitochondrial myopathies are usually diagnosed in children and adolescents. Pathology affects the muscle fibers of the eyeball and the muscles of the extremities. Other organs may also be included in the pathological process: kidneys (tubulopathy), heart (cardiomyopathy), liver, central nervous system (epileptic seizures, dementia, cerebellar ataxia, myoclonia), auditory analyzer (sensorineural hearing loss). During physical exertion, the patient may experience shortness of breath and headache, which in its manifestations resembles a migraine.

Mitochondrial myopathy is characterized by muscle weakness, which may be limited and widespread. In the case of the widespread nature of muscle weakness, the patient complains of poor exercise tolerance and excessive fatigue. With a limited nature of pathology, there is a local lesion of the muscles of the face, limbs and eyeball.

Metabolic myopathy
Metabolic myopathy, like most other neurological pathologies, is accompanied by a deficiency of lipid fractions. This is often manifested by a sharp decrease in the ability to perform physical exercises. The most common cases of lipid metabolism disorders are deficiency of the enzyme KPT and carnitine. Carnitine deficiency syndrome is characterized by the progression of muscle weakness, damage to the pharyngeal and facial muscles, as well as the muscles of the extremities. With a lack of CBT, the patient feels severe pain due to physical exertion.

Another manifestation of metabolic myopathy is a violation of glucose and glycogen metabolism. If the patient has an excessive accumulation of glycogen, then at rest he feels fine. In case of enzyme deficiency with increased activity, patients complain of muscle weakness and excessive fatigue. If physical exertion is not stopped in this case, muscle contracture may occur, which will lead to serious damage to muscle tissue.

McArdle’s disease
McArdle’s disease will be characterized by severe muscle pain, as well as weakness and the formation of seals. During physical exertion, patients may even experience muscle breakdown, signs of myoglobinuria and kidney failure may appear. Pathology can also manifest itself as a violation of the cardiovascular system: heart failure or weakness of the heart muscles.

Andersen and Cory-Forbes disease
It has a very complicated course, since the patient has extremely severe liver and heart lesions. Moderate muscle lesions and physical development disorders are also observed in children’s patients. The infant form of the disease is characterized by maltase deficiency. It usually develops immediately after the birth of the baby and is accompanied by life-threatening symptoms such as congestive heart and muscle weakness.

Almost always, the disease progresses rapidly and ends with the death of the child. Life expectancy in case of maltase deficiency is no more than two years. No less severe manifestations of metabolic myopathy, which also occur at an early age, will be weakness of the lower extremities and serious respiratory disorders. If maltase deficiency occurs in adult patients, then they have weakness of the lower extremities and muscle girdle.

Diagnosis of metabolic myopathies
The diagnosis is made on the basis of a thorough clinical examination of the patient, as well as anamnesis of the disease. The most pronounced clinical signs of pathology are seizures, weakness, severe muscle pain, and a change in the color of urine. The patient must be prescribed an additional detailed neurological examination. To confirm the diagnosis, the neurologist prescribes a study of enzymatic activity: a blood test for AST, CK, ALT, LDH.

Electroneurography and electromyography are considered to be effective diagnostic techniques, which allow us to accurately determine the most characteristic deviations for myopathy. To detect various kinds of organic changes, doctors prescribe CT or MRI of the brain. According to the indications, an additional tomographic examination of the internal organs can be carried out.

The most accurate information about the disease can be obtained by muscle biopsy, as well as subsequent microscopic, morphological, histochemical examination. Thanks to this technique, the doctor manages to make a final diagnosis. To make a diagnosis and differential diagnosis, a neurologist may need to consult a cardiologist, a nephrologist, an ophthalmologist, a geneticist, a pediatric neurologist. It is extremely important to identify the disease at its early stage, because this allows you to choose the optimal way to treat it.

Treatment of metabolic myopathies
To date, there are no effective methods for the treatment of congenital metabolic myopathies. If a patient has been found to have this form of the disease, he is prescribed only symptomatic therapy. The patient will need to follow a special diet, which provides for the predominance of foods with a high protein content in the diet. The intake of fructose and multivitamins is also indicated. If a patient has myoglobinuria, he is additionally injected with fluid to prevent kidney failure and maintain normal diuresis.

To eliminate the symptoms of mitochondrial myopathies, the patient is credited with drug therapy, which involves taking drugs that improve energy metabolism (ubiquinone, L-carnitine, thiamine, riboflavin, vitamins C and E). According to the doctor’s indications, orthopedic correction may also be prescribed. Treatment of acquired diseases is based on a different principle: therapy is not aimed at eliminating symptoms, but at treating the underlying disease that caused metabolic myopathy.

Prognosis and prevention of metabolic myopathies
The prognosis for patients with different forms of metabolic myopathies is often unfavorable. The disease that has arisen in the first weeks of an infant’s life is especially difficult to treat. Infantile forms of metabolic myopathies are fatal — usually patients die at an early age. As for the late forms of the disease, they have a much more favorable prognosis. The positive outcome of the disease also depends on the involvement of pathologies of the heart, kidneys, liver and other organs in it.

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