Spinal Muscular Atrophy
Respiratory muscle weakness
In several forms of SMA, respiratory muscle weakness is a significant problem. It’s the most common cause of death in types 1 and type 2 chromosome 5 (SMN-related) SMA.
When the respiratory muscles weaken, air doesn’t move into and out of the lungs very well, with subsequent adverse effects on general health. Signs of weakening respiratory muscles are headaches, difficulty sleeping at night, excess sleepiness during the day, poor concentration, chest infections and, eventually, heart damage and respiratory failure.
Often, in infantile-onset SMA, the muscles between the baby's ribs are very weak, while the diaphragm muscle stays fairly strong. This leads to children who appear to be breathing by moving their bellies rather than their chests and to a pear-shaped body in these infants.
In recent years, the availability of portable, effective ventilation devices has created more options for newborns with SMA, and some have surprised their families and physicians by living many years.
Assisted ventilation also can help children and adults with different forms of SMA. Many physicians advise starting out with noninvasive ventilation, which generally means that air (usually room air, not enriched with oxygen) is delivered under pressure through a mask or mouthpiece.
This kind of system comes in many forms and can be used as many hours of the day and/or night as necessary. It can easily be removed for eating, drinking and talking.
When noninvasive ventilation isn’t sufficient, ventilation assistance can delivered through a tracheostomy — a surgical hole in the trachea, or windpipe. Air under pressure is then delivered through a tube in the tracheostomy site. After a period of adjustment, it’s usually possible for people to eat, drink and talk with a tracheostomy tube.
Other necessary aspects of respiratory care in SMA include clearance of respiratory secretions, sometimes also achieved with a mechanical device, and prevention of infection as far as possible.
An insufflator-exsufflator is one type of device that can assist with clearing respiratory secretions from the airway. The device applies positive pressure to the airway and then rapidly reverses to negative pressure, mimicking a natural cough. The CoughAssist, made by Philips Respironics, is an example of this type of device.
Another type of airway clearance aid is a high-frequency chest wall oscillation device. This device is a vest that rapidly inflates and deflates, vibrating the chest and creating "mini-coughs" that dislodge mucus from small airways, moving it toward larger airways from which it can be more easily coughed out. The Vest Airway Clearance System, made by Hill-Rom, is an example.
To prevent respiratory infections, almost everyone with SMA should get a flu shot every year. Other precautions include staying away from crowds and getting adequate rest and nutrition.
The MDA clinic team can advise you about respiratory care, flu shots and related matters.
Swallowing muscle weakness
Swallowing problems occur when the muscles of the mouth and throat are weak.
Babies with infantile-onset SMA usually have trouble swallowing and sucking. Sucking weakness can lead to dehydration and poor nutrition, while swallowing weakness can lead to obstruction of the airway and respiratory infections from inhaled food or liquids (aspiration).
Babies with severe swallowing and sucking weakness can be fed by alternative methods, such as a feeding tube, often called a gastrostomy tube or g-tube. A feeding tube is a small, flexible tube, about the diameter of a pencil, that allows liquid nutrition (homemade or commercially prepared) to enter the stomach directly, bypassing the mouth, throat and esophagus. Some feeding tube systems are constructed so that the tube can be detached from a "button" on the abdomen when it’s not in use.
Some g-tube users also can eat and drink by mouth, in addition to using the tube. If the main problem is weakness of the chewing muscles, making eating laborious and time-consuming, then it’s fine to eat by mouth for pleasure and extra nutrition, and use the g-tube for basic calories. By contrast, if the main reason for the tube is aspiration of food and liquid, then it’s probably not safe to eat and drink by mouth.
Speech-language pathologists (SLPs) are educated in treating swallowing problems as well as those associated with speech.
Your MDA clinic team can advise you about swallowing muscle weakness, including special ways of preparing food and the use of gastrostomy tubes.
Back muscle weakness with progressive spinal curvature
Weakness of the muscles of the back that normally support the flexible, growing spine is a major problem in childhood-onset SMA. If it’s not corrected, the child may develop scoliosis — a side-to-side curvature of the spine — or kyphosis, a forward curvature of the spine, or both. Some may even end up with "pretzel" types of curvatures that make it impossible to sit or lie down with comfort.
Some physicians believe that severe spinal curvatures may compromise respiratory function in some cases, if the curved spine compresses a lung.
A back brace or corset that supports the child in a certain position is often prescribed to try to direct the spine as it’s growing. Braces don’t solve the problem, but they may slow the progression of a curve.
The permanent solution to spinal curvature is almost always spine-straightening surgery, which can be done if the child’s respiratory status is good enough to withstand the surgery.
The timing of back surgery is tricky. Doctors generally like to wait until maximum spinal growth has been achieved because that allows a simpler surgical technique to be used. On the other hand, if respiratory status is deteriorating, surgery often can’t wait until growth is complete. Here again, the MDA clinic can help you decide.
A child or adult with SMA who must undergo surgery (for example, to correct scoliosis) needs to take special precautions. The surgical team, particularly the anesthesiologist, must thoroughly understand SMA.
Sometimes, especially in the early stages of SMA, the muscle cells that aren’t receiving nerve signals develop certain abnormalities as they try to "reach out" to nerves. These abnormalities can lead to dangerous reactions to muscle-relaxing drugs often used during surgery. Doctors can get around this problem, if they’re aware of it, by using different drugs.
Can diet help?
Many people wonder if a special diet will affect the course of SMA. While it’s certainly true that children and adults with SMA need good nutrition, so far, there’s little evidence to suggest that any particular type of diet is useful against SMA — and in fact some diets may be harmful.
For example, special formulas made up of broken-down protein components called amino acids — so-called "elemental diets" — actually may cause problems for children with SMA who have little muscle tissue. Some experts say blood levels of these amino acids can become too high if there isn’t enough muscle tissue to properly use them.
Children and adults with SMA run the risk of becoming overweight, probably because they can’t exercise effectively and are taking in too many calories for their level of activity. With the guidance of a physician or nutritionist, it should be possible to keep weight under control, which is important for health, appearance and the backs of caregivers who help with lifting and transferring.
Some children may do better with small, frequent feedings than with three large meals a day. In addition, some physicians recommend over-the-counter supplements, including creatine and/or coenzyme Q10, to meet nutritional needs.
Your MDA clinic physician and other staff members at the clinic can help you with nutritional issues for yourself or your child.
How much and what kinds of activity are best?
In SMA, most physicians advise that doing as much physical activity as is comfortable without going to extremes is a good idea, in order to maintain general physical and psychological health and well-being.
It’s important to protect joints from stiffness or injury, preserve range of motion (flexibility in the joints), maintain circulation and, especially for children, allow enough mobility for exploration of the environment.
Exercising in a warm pool (85 to 90 degrees) may be particularly beneficial. A person with SMA shouldn’t swim alone, and appropriate safety precautions should be provided.
While some physical therapy experts believe over-exercising muscles is not a problem, others believe exercising to exhaustion can "burn out" remaining motor neurons before their time. More research is needed in this area; in the meantime, it seems sensible to exercise with discretion and stop before reaching the point of exhaustion.
For more information, see Exercising with a Muscle Disease.
Physical therapy and occupational therapy programs can help children and adults learn the best ways to maximize their muscle function and accomplish activities of daily living. A referral to a physical or occupational therapist can be obtained through your MDA clinic.
An array of assistive technology products can help even very young children explore the world despite having very weak muscles. Standers, walkers, various kinds of powered and manual wheeled vehicles, and braces (orthoses) can help with standing and moving around. Therapists also can help teachers and parents find the best physical solutions for the school environment.
Other useful technology can help with writing, painting, using a computer or telephone, and electronically controlling the environment (for example, temperature, lighting, television and so forth).