Overview.
Pseudohypertrophic muscular dystrophy includes Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD), with the former being the most common clinical condition. It is an X-linked recessive myopathy that originates in muscle tissue. It is an inherited disease, mostly X-linked recessive, but individually chromosomally recessive.DMD and BMD are allelic diseases.Gowers’ sign: Children with this disease have a characteristic rising maneuver when sitting up from the supine position, i.e., the child is unable to sit up directly from the supine position, and needs to first roll over into the prone position, then squat, and then switch to a four-point supportive position.The disease is characterized by the following symptoms: the child is not able to sit up directly from the supine position, but needs to first roll over into the prone position, then squat, and then switch to a four-point supportive position. Pseudohypertrophy of the gastrocnemius muscle: The majority of children have pseudohypertrophy of the gastrocnemius muscle, which can be seen bilaterally. This is due to the atrophied muscle fibers being filled with fat, and there is a decrease in muscle strength, but it is firm to touch.
Etiology
It is an X-linked recessive myopathy that originates in muscle tissue. It is a hereditary disease, mostly X-linked recessive, but individually chromosomally recessive.
Symptoms
1. Skeletal muscle
DMD patients with childhood onset, usually at the age of 4 to 6 years old, walking easy to fall, running difficulties, gradually appear walking and going up the stairs, squatting and standing up difficulties. Neurological examination reveals low muscle strength of the limbs, muscle atrophy and weakened tendon reflexes. The pelvic girdle muscles were weak and showed a typical duck step, the shoulder girdle muscles were atrophic and weak to form a winged shoulder or free shoulder, and the atrophy and weakness of the abdominal muscles and iliopsoas muscles formed the characteristic Gowers’ sign. The vast majority of children have pseudohypertrophy of gastrocnemius muscle, and a small number of children can see pseudohypertrophy of lingual muscle or deltoid muscle.
2. Heart
The majority of DMD patients have no cardiovascular symptoms. Heart failure and arrhythmias occur only in the late stages of the disease and in the stress of recurrent infections.
3. Gastrointestinal tract
The smooth muscle of the gastrointestinal tract can also be involved. Acute gastric dilatation can be fatal, and autopsies of patients who die from this condition show degenerative changes in the outer layer of the longitudinal muscles of the stomach. Some patients may have severe constipation.
4. Nervous system
Patients with DMD and BMD may have central nervous system dysfunction, especially mental retardation, with a mean IQ of less than 1 standard deviation from normal. The incidence of epilepsy is increased, especially in BMD. DMD patients are prone to emotional and behavioral problems, cognitive decline and learning difficulties.
5. Other
Patients with DMD who can walk have a mild decrease in lumbar spine bone density, while those who cannot walk have a significant decrease.
Examination
1. Serum biochemical tests
Creatine phosphokinase (CK) is markedly elevated, reaching 15,000 to 20,000 U/L or even higher. Serum CK is elevated at birth and decreases slightly in the later stages of the disease.
2. Muscle biopsy
Characteristic pathological changes include scattered degenerative changes and necrotic muscle fibers. Over time, there is an increase in intramuscular connective tissue as well as loss of muscle fibers and replacement by adipose tissue.
3. Genetic diagnosis
In China, quantitative PCR and short tandem repeat sequence chain analysis have been applied to detect DMD gene carriers.
4. Electromyography
Myogenic changes, the lesion muscle is low potential, waveform duration is shortened, and polyphasic wave is increased.
Diagnosis
Diagnosis can be made on the basis of etiology, clinical manifestations and laboratory tests.
Treatment
1. Drug treatment
Commonly used drugs include vitamin E, inosine, adenosine triphosphate and traditional Chinese medicine. The use of adrenocorticotropic hormone and biphenyl diacetate can reduce serum enzyme levels. Early administration of sodium lactate has been proposed to enhance the muscle strength of patients. In addition, treatment with the calcium antagonist verapamil has been shown to be effective. However, the above treatments can only delay the progression of the disease and cannot cure the disease at all.
2.Supportive treatment
In order to maintain muscle function and prevent contracture, moderate exercise is very important and prolonged lying in bed is not recommended. Symptomatic treatment includes passive exercise and massage of muscles and joints, as well as attention to and prevention of complications.
3. Surgical treatment
Patients with DMD often develop progressive scoliosis, which often requires posterior spinal fusion.
4. Gene therapy
Gene therapy for DMD, ranging from direct injection of plasmids to transfection of the DMD gene assembled with different types of vectors, has been successful in animal experiments, with dystrophin being expressed in the skeletal muscle of animals. Extensive research has also been carried out in finding suitable vectors, and the search for the most suitable vector to improve expression efficiency and overcome immune rejection is still ongoing.