Spinal Muscular Atrophy

By: Ann K. Bowman


Spinal muscular atrophy is a group of hereditary conditions that causes weakness that usually leads to wasting of muscle. These conditions can have an onset in adult hood in some cases, however much more prevalent in infants and children. Spinal muscular atrophy can be divided into several categories, differentiated by age of onset and severity of symptoms. The onset tends to be abrupt and the progression is usually slow. (7,2)


The incidence has been estimated between 1 in 6,000 and 1 in 10,000. (2)


As a group of hereditary diseases are caused by genetic mutation.(7)


A missing or abnormal gene known as a survival motor neuron (SMN). SMN I and SMN II help with maintenance or motor neurons. SMN I is more prominent then SMN II, therefore SMN I is the neuron that is most effected.(7) Researchers have found that the more SMN II the less severe the symptoms are.(3)


Caused by an abnormal repeat of CAG (>40), which leads to a decrease in cellular functions such as transcription and axonal transport. This will also increase the number of proteins. The more excess proteins the more depolarized the mitochondria and the more severe the symptoms. (3) Histopathological findings show loss of anterior horns in the brainstem and the spinal cord.


There is a mutation of UBA 1, which provides proteins that help contruct enzymes to break down proteins that are needed to be broken down. (3) If there is too much protein in the cell, it will lead to premature cell death, which overtime leads to weakness.(3)


Is caused by a mutation of VAPB gene which causes misfolding or unfolding of proteins, accumulating proteins to the point that normal function will be impaired. (3)



Also known as infantile-onset spinal muscular atrophy or Werdnig-Hoffman Disease. Type I is usually diagnoses by 6 months old. These babies tend to have "floppy" limbs, trunk, swallowing difficulties and weak suckling reflex and be tachycardic.(8) Type I can be generalized into three groups.

Subgroup I

This subgroup of TYPE I SMA have the most severe symptoms. These babies require neonatal ventilation support. (5)

Subgroup II

These babies have poor head control, difficulty handling secretions, and have problems during feeding. At some point, these babies will need noninvasive respiratory support.(5)

Subgroup III

Out of the three subgroups for Type I SMA, these subgroup has the best prognosis. These babies are able to achieve head control, that over time will regress.(5)

Type I babies without respiratory therapy die from respiratory therapy in two years. (7) Decrease in respiratory abilities is due to a development of bulbar weakness and dysphagia. This leads to an ineffective cough, mostly at night. That will progress to happen during the day and night.(8) It is advised for parent to learn how to use pulse oximeters for all of Type I children. Reason being that once the oxygen saturation falls below 94%, noninvasive ventilation is recommended, which may over time also improve lung function. (8)


Also known as Juvenile spinal muscular atrophy, intermediate spinal muscular atrophy or chronic spinal muscular atrophy. Generally speaking the later the onset of onset of symptoms, the less severe the symptoms are and the better the prognosis.(7,2) Usually the onset of symptoms is between 6 to 18 months.(2) The lower extremities tend to be more effected then the upper extremity. However, the first indication to the babies caretaker that something is wrong, is when the babies are not able to crawl or walk. (2) When the babies are placed into sitting up, they are able to stay up. But they are not able to get into the sitting up position themselves. (7) If symptoms do not start to occur until closer to 18 months then the baby will be able to walk and be fully functional. As the condition progresses their ability to walk and function will decrease. (2) For this reason a pulse oximeter should be used to monitor oxygen saturation. Once the oxygen saturation gets below 94%, noninvasive ventilation needs to be considered.(5)


Also known as Wolhfark-Kubelberg Welander disease or mild spinal muscular atrophy.(2) Onset of symptoms can happen anytime from toddler to late adolescence.(2,7) This type of spinal muscular atrophy is the most mild form of the condition. People with this condition are able to stand and walk alone. However they may need an aid when getting up from sitting.(7) With the progression of the condition there is an increase vulnerability to infectious diseases, and will lose walking ability later in life. (2,7)


Also known as Kennedy Disease. Age of onset in between 30 and 50 years old. (2,3) Signs and symptoms include muscle weakness, tremor and twitching, usually in the tongue and proximal musculature. (2,3) Fatigue, decreased deep tendon reflex with no pathological reflex is common, dyarthria, dysphagia, handing jaw, fasculuations and flexor muscle cramps. (3) Is more common in males than in females. Females tend to be asymptomatic even when homozygous. In males additional symptoms may include testicular atrophy, impotence, and decreased infertility.(3) Even though the condition has a slow progression there is an increase respiratory vulnerability which is often what leads to death.(3) Often around 49 years old, individuals may need to use a handrail in order to ascend stairs. Around 59 years old individuals may need to use a cane. And around 61 years old a wheel chair may be required.(3)


Onset of symptoms is around six weeks to six months. It is possible, but rare to show symptoms into late adolescence.(2) It is a slow progressive condition that starts in the hands and feel and progresses proximally.(2) The condition can lead to paralysis of the diaphragm and eventually respiratory failure.(2)


Is an X-linked spinal muscular atrophy. This includes spinal muscular atrophy with cerebellar hypoplasm, diaphragmatic syndrome. Onset in adult males that have similar feature to individuals with Type I spinal muscular atrophy. (7) In severe causes born with broken bones. People with this condition have poor muscle tone at birth. (2)


With progression of spinal muscular atrophy the point of inability to clear secretions is because of increase weakness in intercostal muscles. The diaphragm seems to not be affected. The chest wall will "collapse". (8) Causing a bell shaped chest and pectoral encavatum. (8) Signs of having increase difficulty with respiration includes hypoventaliation during sleep. Respiratory difficulties are exacerbated with undeveloped chest, lungs and recurrent infections.


1)Using a cough assist machine= have 4 sets of 5 breaths, followed by oral suction of secretions.
2)Chest physical therapy
3)Using a cough assist machine= have 4 sets of 5 breaths, followed by oral suction of secretions.
4)Postural drainage in trendelenberg position for mechanical advantage. For 15-20 minutes as tolerated.
5)Using a cough assist machine= have 4 sets of 5 breaths, followed by oral suction of secretions.

Complications with this include gastric desenetation, emesis resulting in aspiration, pneumonia and death. (8)


Clinical neurological exam and nerve conduction studies, to ensure that the muscle atrophy is not related to a neurological condition. Blood test and molecular genetic investigations for any mutations or deletions. (7,8)



Depending on the severity of the conditions, respiratory therapy to aid in clearing secretions. Almost of these children will have to have passive range of motion as part of their physical therapy since they are prone to contractures. (1,8) For Type I spinal muscular atrophy, the funciton outcome tool used is the Children's Hospital of Philadelphia Test of Strength.(5)


The aim of physical therapy for most of these children will be to delay spinal fusion until at least they are ten years old, or older. (1) These children are also prone to scoliosis. In order to reduce the progression rate a lightweight custom molded plastic thoracolumbar orthoses will help with sitting balance. Before fitting children for the orthoses one needs to find out about fatigue, total sitting tolerance and dyspnea. If the individual is able to ambulate than a lightweight KAFO to stabilize the knees and ankle. It should be noted that these children are also prone in intermittent spontaneous hip dislocation. (1) Functional outcome measurement tools that are often used for Type III spinal muscular atrophy is the Gross Motor Functions for ambulating patients. For Non ambulating patients the Hammersmith Functional Motor scale and quantitative muscle testing. (5)


Individuals will probably focus on walking aid in physical therapy. Depending on the progression of the condition, respiratory therapy may end up as part of the physical therapy. (5) Functional outcome measurement tools that are often used for Type III spinal muscular atrophy is the Gross Motor Functions for ambulating patients. For Non ambulating patients the Hammersmith Functional Motor scale and quantitative muscle testing. (5)

Modalities Used

Modalities in general are physical agents that are used injunction with physical therapy intervention. These physical agents include thermotherapy (heat), cyrotherapy (cold), ultrasound, Electrical Stimulation, TENS, and aquatic therapy. Because of the nature of spinal muscular atrophy very little research has been done on the effect of using modalities on this population.

Thermotherapy (heat).

No research has been done to show the direct relationship of the effects of thermotherapy on patients with spinal muscular atrophy. Heat is generally used for musculoskeletal pain, or increasing range of motion.(9)

Cyrotherapy (cold).

No research has been done to show the direct relationship of the effects of cyrotherapy on patients with spinal muscular atrophy. Cold is generally used for decreasing inflammation, and swelling. (9)


The basics of ultrasound is that from the ultrasound head called a transducer high-frequency sounds waves are sent out. A picture is created based from the echos of the sound waves bouncing off of the tissues. The intensity of the echoing is based off of the acoustic properties of the tissues as well as density. A computer program takes all of the echoing as data and creates a picture. Due to the nature of the condition of spinal muscular atrophy, ultrasound is not used as a treatment. However, it is being used as a diagnostic tool. In the early stages of the disorder, the ultrasound may appear normal. During the later stages of spinal muscular atrophy the ultrasound will be able to show the amount of atophy since it is a reliable tool for muscle thickness.(10) The quadriceps show the most amount of atrophy. There is also Dynamic muscle ultrasound. Which is used to look at the quality of muscle contractions during movements. Some suggest that dynamic muscle ultrasound may be more sensitive than EMG because you are able to see a larger area of muscle than a needle.(10)

Electrical Stimulation.

Is often used in order for muscular conditioning. Usually in conjunction with an exercise program as long as the muscle group is innervated. Depending on the amplitude of wave, pulse width, duration, frequency and the size of the pads, it can range from a relaxing experience (pain reduction), to painful (usually used in order for strength gains). Spinal muscular atrophy is a condition that affects children into adulthood. The literature that I was able to find choose to use a low-intensity therapeutic stimulation overnight. This has worked in children with other disorders such as cerebral palsy and spina bifida. As a result of the study, it was concluded that TES was not more effective for strength gains over the control group, which received an exercise program. There was a trend that was noticed that patients who received TES had more control over 12 months than those in the control group. The study stated that the TES was used for 4 hours a night. According to studies concluding that TES worked for patients with cerebral palsy and spina bifida the minimum was 5 hours a night. It has been put on the table that if the patients were to be using the TES a minimum of 5 hours a night, more statistical significance for difference in strength gains would have been found.(11)

Aquatic Therapy.

The basics of aquatic therapy is that water provides a gravity limited environment. This allows patients who do not have the strength to go against gravity to move through normal range of motion. The water also provides a little resistance when performing activities such as walking. With time the patient will be able to build enough strength to go against gravity in the gravity limited environment. At that point than land based activities can be begin and progressed. For patients with Type III spinal muscular atrophy this has been suggested as helpful. However in the case study the patient was also receiving land based therapy. Therefore it can't be said that aquatic therapy by itself will be all the patient will need for intervention. However, the aquatic based therapy exercises focused on function such as walking, jumping and standing. All of these items improved more than other issues that the land therapy alone focused on such as lying, rolling and breathing.(12)

A Father Helping Clearing Secretions From His Daughter, Part I

A Father Helping Clearing Secretions From His Daughter, Part II


For Spinal Muscular Atrophy there are several types of medications that are currently being explored and are trying to get approval for clinical trials. Some medications are being engineered to stimulate production of SMN protiens from SMN II gene, because SMN I and SMN II are very similar. (7) Histone Deacetylase has been developed and is being tested in order to extend the half life of SMN II. The hopes is that this will allow more SMN II be around therefore decreasing the severity of spinal muscular atrophy.(4) Also aminogiycerides have shown to increase the number of SMN II, therefore improving motor function in mice models.(4)
Stem cells have been looked into as a possibility. When stem cells have been injected into the spine, an increase in weight gain, increase in muscular hypertrophy and an increase in lifespan have been shown. (4)

Gross Motor Functions (88 Items)



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5)Montes et al. Clinical Outcome Measures in Spinal Musuclar Atrophy. 2009; 24 (8). Journal of Child Neurology.
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12) Salem, Y. Gropacl, S. Aquatic therapy for a child with Type III spinal Muscular Atrophy: A Case Report. 2010. (30) 4: 313-324. Physical & Occupational Therapy in Pediatrics.

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