Montanna at the Melbourne Royal Childrens Hospital (April 2005)Picture by Shazz Brownlaw.
Spinal Muscular Atrophy
- By Rhiannon Taggert RN Div 1,
Royal Children's Hospital.
(Melbourne, Australia.)
Spinal Muscular Atrophy (most commonly known as SMA) is a genetic motor neurone Disease that causes progressive deterioration of motor neurons in the spinal cord. It results in weakness and wasting of the voluntary muscles.
It is the number one genetic Killer of children under the age of 2.
SMA is not a disease of the brain, the muscles or the sensory nerves. However, the muscles do eventually weaken and get smaller (atrophy) as they do not receive stimulation from motor neurons. Normally, these motor neurons relay signals, which they receive from the brain, to the muscle cells, which promote movement in our limbs, chest, throat, face and mouth. When these neurons fail to function the muscles deteriorate. SMA affects the muscles throughout the body, although the proximal muscles (those closest to the trunk of one's body- i.e. shoulders, hips, and back) are often the most severely affected.
The brain is not affected by SMA, and there have been tests to show these children have at least average to above average intelligence. It also does not affect the sensory nerves, so children have a normal feeling of touch, temperature, and pain. To look at, these children do not have visible deformities, they are just extremely weak.
There are four "types" of SMA: Type1, Type 2, Type 3, and Type 4. The earlier the symptoms of SMA are noticed, the more severe the type of SMA.
SMA Type1
Also known as Infantile SMA or Werndnig- Hoffman disease, this is the most severe form of SMA. Type 1 children are diagnosed usually before 6 months of age, and more likely before 3 months of age. Symptoms can even start in the womb when mothers note decreased movement in their final months of pregnancy. Usually a child with Type 1 is never able to lift their head or accomplish the normal motor skills expected in early infancy. Generally they have poor head control, and may not kick their legs very much or be able to bear any weight on their legs. They do not achieve the ability of sitting up unsupported. All their muscles are extremely weak, with the weakest being the legs, upper arms and neck.
SMA affects all muscle systems including sucking, swallowing, digesting food and excretion. As the disease progresses, swallowing and feeding may become difficult and children will often have trouble controlling their secretions. Constipation is a big factor of SMA as is getting proper nutrition and calories for proper weight gain.
There is a weakness of the intercostals muscles (the muscles between the ribs) that help to expand the chest. The strongest breathing muscle in SMA is the diaphragm. As a result the child appears to breathe with their stomach. These children's chests may appear concave (sunken in) due to the diaphragmatic breathing. Due to this type of breathing, the lungs may not fully develop, and their cough is very weak. This can make it difficult to take in adequate amounts of oxygen while sleeping.
The physical characteristics that can often give these children away are a bell shaped body, breathing with their stomach instead of their chest, movement from the elbows down in the arms, legs that appear to sit in a "frog" position, clenched hands, facilitations, of the tongue (where the tongue appears to vibrate rapidly), and a head which tilts to the side due to a lack of neck muscles. These children however often have very bright and expressive faces.
A common cold can quickly turn into pneumonia, which is what usually takes the lives of these children along with respiratory failure when they no longer have the muscles to be able to breathe on their own.
The major decisions for parents of a child with SMA is whether or not to insert a feeding tube such as a nasogastric tube to prevent starvation once the inability to swallow occurs, and whether or not to put them onto a ventilator once they experience respiratory failure.
Currently the average age a child with SMA Type 1 will survive without being put on a ventilator is 8 months. Of course there are exceptions who may live to nearly 2 years, but this is extremely rare. SMA affects each child so differently, that they do not always follow the same path or progression.
SMA Type 2
Also known as Intermediate SMA or Chronic childhood SMA. Type 2 children are usually diagnosed before 2 years of age. Usually they can stay in a sitting position without support, but they can't actually get there without assistance. With the aid of assistance or bracing these children may be able to stand, but will usually never walk. Parents often initially notice the children become hypotonic, meaning floppy or limp. They usually don't have swallowing problems, but it can vary from child to child.
For the children with swallowing problems, a nasogastric tube may be required. Due to the weakness of the muscles supporting the bones of the spinal column, scoliosis (curvature of the spine) often develops in children who are wheelchair bound. As with all forms of SMA, weakness increases over time. There however is no lifespan of a child with SMA type 2, as it varies so widely. They could pass away at an early age or live into adulthood depending on how severely they are affected. Physical growth continues at a normal pace.
SMA Type 3
Also known as Kugelberg-Welander or Juvenile SMA. SMA Type 3 is variable with its onset and children can be diagnosed from between 18 months and up until early adolescence. However most are diagnosed before three years. These children can stand alone and walk, but may show difficulty at some stage. Most early milestones are reached at regular times. When they begin walking, they might fall frequently, have difficulty getting up from a sitting position on the floor and may be unable to run. Feeding and swallowing difficulties in this type of SMA are very uncommon. They can sometimes loose that ability to walk later in childhood, adolescence or even adulthood, as the muscles degenerate.
SMA Type 4
Also known as Adult onset SMA. Type 4 is much less common than other forms of SMA The symptoms typically begin after the age of 35. It has a very slow progression, and the muscles used for swallowing and respiratory function are rarely affected. They usually have a normal lifespan, with the weakening of their muscles.
What is the cause of Spinal Muscular Atrophy?
SMA is a "Recessive" genetic disease, meaning that both parents must carry a copy of the recessive SMA gene. SMA is caused by an abnormality of the Survival Motor Neuron 1 gene(the SMN1 gene). When the SMN1 gene has decreased or no function, then the motor neurons in the spinal cord and brainstem do not survive and gradually die off. SMN1 is located on chromosome 5.
Everyone has two copies of this gene. But in SMA children, they have two faulty copies, which were inherited from both their parents. Their parents were not affected however, as they only had one faulty gene, and therefore were only carriers.
If two carriers have children, there is a 25% chance of having a child with SMA, which also means there is a 75% chance that they wil have a healthy child. One out of 40 people are a carrier of this recessive gene.
How is Spinal Muscular Atrophy diagnosed?
SMA is usually suspected due to the early history of weakness or lethargy. It is then diagnosed through a blood test, which looks for the presence or absence of the SMN1 gene, along with a physical examination. This test cannot actually tell the type of SMA that is diagnosed, by the onset and degree of the disease. It accurately diagnoses SMA in 95% of cases. If the result is positive it is 100% correct.
Often if the test result is negative it may be necessary for the following tests to be performed. Other tests that are available include: " Electromyography- This measures the electrical activity of the muscle by inserting small needles into the muscles (usually arms and thighs) while an electrical pattern is observed and recorded by a specialist. " Muscle Biopsy- used to check for degeneration of muscles. " Needle Biopsy- an alternative to the muscle biopsy, using a small needle instead of a 2-3 inch incision.
Is there a cure for Spinal Muscular Atrophy?
Unfortunately there is no cure for SMA. Treatment therefore revolves around treating child's symptoms and keeping them comfortable and happy. The treatment given to each child depends on the families wishes. There are three basic options of care and treatment:
" Palliative care or comfort care - Parents may choose this option if they do not wish to intervene in their child's illness. With no intervention, a child with SMA Type 1 has a life expectancy of 8 months. Parents' will often choose to use oxygen and pain medications such as morphine to keep their child comfortable. Often these parents believe their child's quality of life would be poor, so they choose to let nature take its course.
" Non-Invasive Protocol - A respiratory protocol using the breathing machine called "BiPap" and a machine called "Cough Assist" to help manage their respiratory issues along with the use of physiotherapy. Parents often choose these machines as a method of providing respiratory comfort and strength for their child. This is often chosen by parents who do not wish to put their child through a surgical procedure, and believe they can provide a good quality of life for their child by improving their respiratory function.
" Tracheotomy and permanent ventilation - A surgical procedure, creating a hole in the throat, which can provide breathing assistance via permanent ventilator if needed. This method is often chosen by parents who believe that their child is receiving good quality of life, simply by being alive and having improved respiratory function.
It is also very common for a child with SMA to have a nasogastric tube inserted once their swallowing reflexes have gone. This enables them to receive the nutrient requirements their bodies need. It is a simple yet effective treatment.
What is "BiPAP" and how does it help?
BiPAP stands for Bi - level Positive Airway Pressure. It uses a mask with a cap, which fits over the head to hold it in place.
BiPAP provides a higher volume of air into the lungs during inhalation and inflates the lungs greater than what the child can do on their own. During exhalation, the BiPAP pressure drops so that the air can passively leave the lungs. The BiPAP machine can sense when a person is taking a breath and give the breath in synchrony with the child. A respiratory rate is also set so that the Bi PAP gives a minimum number of breaths per minute. The person can breathe above that rate however and the BiPAP will deliver more breaths.
What is the cough Machine and how does it help?
Also known as the In/Exsufflator, this machine stimulates a cough by delivering a deep breath of air into the lungs and then switching to a negative pressure, which pulls the air out quickly and moves airway secretions and mucus to the point where they can be suctioned from the mouth or the nose.