Spinal muscular atrophy

Introduction Spinal (progressive) muscular atrophy (SMA) is a hereditary, lower motor neuron disease characterized by progressive, symmetrical, proximal-based flaccid paralysis and muscle atrophy, with neuronal death in the spinal cord. Caused. According to the age of onset and the degree of disease, the disease can be divided into 4 types: I-III is called child-type SMA, which belongs to autosomal recessive genetic disease, and its population incidence rate is 1/6000~1/10000, which is in infancy. The most common fatal genetic disease. SMA, which is onset from 20 to 30 years old, is classified as type IV and can be expressed in different genetic modes such as autosomal recessive, dominant and X-linked recessive, and its population incidence rate is about 0.32/10000. Degeneration is limited to alpha motor neurons in the anterior horn of the spinal cord. It is characterized by progressive muscular atrophy and muscle weakness, reflexes disappear, and sensory disturbances do not occur.

Cause

The exact cause is still unclear. The autosomal recessive inheritance of this disease is described. Different cases can be caused by different causes, such as cold, fatigue, infection, lead poisoning, and trauma.

The pathogenesis is that the anterior horn cells of the spinal cord and brainstem motor nuclear degeneration and the number are significantly reduced, but no nerve cell necrosis and glial cell proliferation. The cervical spinal cord is most often involved. Degeneration of the anterior horn of the spinal cord, swelling of the cells, nuclear translocation or disappearance, gliosis, but no inflammatory reaction in the anterior horn and meninges, and no vascular changes. The pyramidal tract has degenerated in some cases, but pyramidal tract signs are rarely found in clinical practice.

an examination

1, symmetrical muscle weakness: reduced autonomic movement, the most proximal muscle involvement.

2, muscle relaxation: the tension is extremely low, the reflection is reduced or disappeared.

3, muscle atrophy: mainly involving the limbs, trunk, followed by the neck, chest muscles.

4, myasthenia gravis, the diaphragm is not tired, the diaphragm muscles are normal, so the chest sinking when exhaling presents contradictory breathing.

5, the course of disease is progressive, advanced medullary muscle atrophy, the most obvious pharyngeal muscle, accompanied by muscle fiber tremor, pharyngeal muscle atrophy caused by breathing and dysphagia, easy to have abscess pneumonia.

Differential diagnosis

Generally in the early or atypical cases of this disease, attention should be paid to the identification of the following diseases:

1. Neonatal myasthenia gravis: The mother is a myasthenia gravis patient, which is related to the anti-Ach receptor antibody in the mother's blood reaching the fetus through the placenta. It usually shows symptoms such as difficulty in sucking, weakness in crying, and decreased movement of limbs after birth. Most children have improved symptoms within 2 to 6 weeks and are effective with cholinesterase inhibitors.

2, congenital dystonia (Oppenheim disease): low muscle tone after birth, no muscle atrophy, no abnormalities in EMG and muscle biopsy.

3, progressive muscular dystrophy: generally in SMA-II, type III children need to pay attention to Duchenne type or Becker type muscular dystrophy. The latter almost all have signs of pseudohypertrophy, and its serum CPK is extremely high, especially in the early stage of the disease, EMG and muscle biopsy are myogenic damage, so the general identification is not difficult. SMA-IV is easily confused with limb-type muscular dystrophy and polymyositis, but it is not difficult to distinguish from clinical manifestations, serum enzymology, EMG and muscle biopsy.

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