Definition
Spinal muscular atrophy (SMA) is one of the nerve-damaging diseases of the central nervous system (brain and spinal cord) and is hereditary. In the course of the disease, nerve cells and the muscles innervated by them are damaged. The disease is relatively rare and shows great variability. It can occur in the first months of life and in adulthood. Basically, the disease leads to a weakening and regression of the musculature, which is why the disease is popularly known as “muscle wasting”.
Forms
Basically, two forms can be distinguished, namely the non – proximal muscular atrophies and the proximal muscular atrophies. In proximal muscular atrophies, the disease starts at the muscle groups near the trunk (proximal), for example in the area of the thigh and the pelvic and hip muscles. Non-proximal muscular atrophies are very rare and initially mostly affect the foot and hand muscles or the shoulder and lower leg muscles. In addition, some rarely occurring forms are known, which are associated with various functional limitations.
Types of spinal muscular atrophy
The proximal muscular atrophies can be divided into 4 different types. These differ with regard to the onset of the disease, the learning of muscular abilities and the possible life expectancy. In type I SMA, the onset of the disease is usually before the age of 6 months.
For example, children suffering from type I cannot hold their head by their own strength. Sitting freely can never be learned and death occurs within the first months of life. Reasons for rapid death can be infections or paralysis of the respiratory muscles.
Characteristic symptoms are pronounced muscle weakness, missing or reduced muscle reflexes and muscle twitches. Good mental abilities of the affected patients are noticeable. The onset of type II disease is within the first 18 months of life.
Muscular atrophy progresses more slowly here than in Type I. Free sitting can be learned, free walking is not possible. It is not uncommon for the muscles to be severely shortened (contractures) and for the spine to change shape (e.g. scoliosis).
Although survival into adulthood is possible, a reduced life expectancy must be expected. Here, the onset of the disease is often after the age of 2 years. Type III shows a significantly milder course.
At the beginning, mainly a weakness in gait and a reduction in muscle reflexes can be observed. Life expectancy is only slightly reduced. Type IV begins at the age of 30 and the ability to walk is maintained. The course and progression of the disease is very variable and can affect different muscle groups. Life expectancy is considered normal.
