What Is Spinal Muscular Atrophy Type 2?

Spinal muscular atrophy (SMA), also known as spinal muscular atrophy, is a class of diseases caused by muscle degeneration and muscle atrophy caused by degeneration of motor neurons in the anterior horn of the spinal cord. It is an autosomal recessive disease and is not uncommon in clinical practice. According to the age of onset and the severity of myasthenia gravis, it is clinically divided into SMA-, SMA-, and SMA- types, namely infantile, intermediate, and juvenile. The common feature is degeneration of the spinal cord anterior horn cells. The clinical manifestations are progressive flaccid paralysis and muscular atrophy, which are progressive, symmetrical, and mainly proximal. Intellectual development and feeling are normal. Different types are determined according to the age of onset, the speed of disease progression, the degree of muscle weakness, and the length of survival. So far, there is no specific effective treatment for this disease. The main treatment measures are to prevent or treat various complications caused by severe muscle weakness, such as pneumonia, malnutrition, skeletal malformation, and psychosocial problems.

Basic Information

nickname

Spinal muscular atrophy

Visiting department

Neurology

Common causes

Autosomal recessive

Common symptoms

Muscle weakness, atrophy

Causes of spinal muscular atrophy

Autosomal recessive inheritance is caused by homozygous deletion of exon 7 of the SMN gene.

Clinical manifestations of spinal muscular atrophy

Most patients with this disease are of type SMA-, followed by type II, with the lowest incidence of type III.

Infantile spinal muscular atrophy

Also called SMA-I or Werdnig-Hoffmann disease. This type is the most serious of type 3, and some cases develop in the uterus, and the fetal movement becomes weak. Half of the cases can occur at birth or in the first few months after birth, and almost all occur within 5 months and can survive 1 Old people are rare. These children have symptoms during the fetal period, reduced fetal movement, obvious limb weakness after birth, difficulty feeding and difficulty breathing. Clinical characteristics:

(1) Symmetrical muscle weakness. First, the lower limbs are affected and progresses rapidly. Active movement is reduced. The proximal muscles are the most affected. They cannot sit alone. Eventually, they develop mild movements in the hands and feet.

(2) Muscles are loose, children with very low tension are in a special position with frog legs, hip abduction, and knee flexion in the supine position, and tendon reflexes are reduced or disappeared.

(3) Muscle atrophy, which can affect the limbs, neck, trunk and chest muscles. Because infants have a lot of subcutaneous fat, muscle atrophy is not easy to detect.

(4) Intercostal muscle paralysis, mild patients may have obvious compensatory abdominal breathing, in addition to severe patients with severe breathing difficulties, visible depression on the sternum during inhalation, that is, paradoxical breathing, and diaphragm muscle movement is always normal.

(5) The motor brain nerve is damaged, and the hypoglossal nerve is the most common, showing atrophy and tremor of the tongue muscle.

(6) The prognosis is poor, the average life expectancy is 18 months, and most die within 2 years.

2. Intermediate spinal muscular atrophy

Also known as SMA-, intermediate SMA or chronic SMA, the onset is slightly later than that of type , and the onset begins more than 1 year old and progresses slowly. The children developed normally at 6 to 8 months. Most cases showed severe muscle weakness, mainly proximal, and lower limbs were heavier than upper limbs. Many children with type II can sit alone, and a few can stand or walk with the help of others, but they cannot walk alone. Multiple micromyoclonus is the main manifestation. Respiratory muscles are not involved in swallowing muscles, facial muscles are not involved, and sphincter function is normal. This type has a relatively benign course of disease with a survival period of more than 4 years and can survive beyond puberty.

3. Juvenile spinal muscular atrophy

Also known as SMA-, also known as Kugelberg-Welander disease, Wohlfart-Kugelberg-Welander syndrome, or mild SMA, is the lightest type of SMA. Symptoms of the disease occur in late childhood or adolescence, beginning with abnormal gait, weakness in the proximal muscles of the lower limbs, slow progression, and gradually affecting the distal lower limbs and upper limbs. Can survive to adulthood. Presented as neuronal proximal muscle atrophy. Walking children with SMA- may have a toddler, lumbar lordosis, raised abdomen, and optional tendon reflexes. The time to maintain independent walking is closely related to the age of onset of muscle weakness. Those with the disease before the age of 2 will not be able to walk around 15 years old, and those with the disease after 2 years of age can keep walking ability to about 50 years old.

Spinal muscular atrophy test

1. Symmetric progressive proximal limb and trunk muscle weakness muscle atrophy, without affecting the facial and extraocular muscles, no reflexes, lack of hypersensory sensation and mental retardation.

2. Family history is consistent with autosomal recessive inheritance.

3. Serum CPK is normal.

4. Electromyography suggests neurogenic damage.

5. Muscle biopsy is consistent with anterior horn cell disease.

Spinal muscular atrophy diagnosis

Generally, those with the above-mentioned typical clinical symptoms and family history, combined with SMN gene analysis, are not difficult to diagnose.

Spinal muscular atrophy treatment

There is no specific treatment for this disease, mainly symptomatic supportive therapy.

Prevent or treat various complications of SMA, prevent lung infections and pressure ulcers, malnutrition, skeletal deformities, mobility disorders and psychosocial problems. If it is accompanied by respiratory insufficiency, an artificial respirator is needed to ensure airway patency and improve respiratory function. Long-term bedridden can cause fallout, and aspiration can also cause pneumonia. Effective measures to prevent pneumonia include assisted cough, chest thump therapy, and intermittent positive pressure ventilation. Even in the absence of acute respiratory infections, patients should maintain good lung ventilation to prevent progressive atelectasis. Once the effective vital capacity is reduced, the risk of pneumonia will increase even if the muscle strength of the limbs or trunk does not change significantly.

Gene therapy or in vitro gene activation therapy will be very promising treatments.