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Spinal Muscular Atrophy

What is Spinal Muscular Atrophy?

Spinal muscular atrophy (SMA) is a genetic (inherited) neuromuscular disease. The large motor nerves of the spinal cord are abnormal in people with SMA because a gene (the Survival Motor Neuron-1 or SMN1 gene) is missing or altered. Without the gene, or with a damaged gene, the nerves do not have a specific protein that allows them to control muscles. The decrease of the SMN1 protein results in improper functioning, and eventually death of the motor nerve cells in the spinal cord. The severity of SMA is related to the amount of the SMN1 protein that is absent in the motor nerve cells (more protein allows for more function). Severity of the disease ranges from mild muscle weakness, to total paralysis and the need for support to breathe.

Signs and Symptoms

Muscle weakness is a hallmark feature of SMA. The muscle weakness is associated with other impairments, such as:

Muscle wasting (atrophy).
Low muscle tone that makes the child’s body feel loose or “floppy” (hypotonia).
Absent or markedly decreased deep tendon reflexes (eg, knee-jerk reflex).
Involuntary tongue movements.
Hand tremors.
Tight joints that do not bend or stretch all the way, or possibly don’t move at all.
Spinal deformity (scoliosis).
Respiratory infections and lung disease.
The course of SMA varies with each individual, and symptoms range from mild to severe. The onset of SMA can occur from birth to adulthood. The progression of the disease varies, but generally as an individual ages, muscle strength decreases and symptoms progress. However, some people with SMA live a normal lifespan.

How Is It Diagnosed?

Diagnosis of SMA begins by observing whether an individual has any of the signs and symptoms of the disease. When SMA is suspected, a simple blood test can identify an estimated 95% of all cases of SMA by revealing the specific mutation that causes the disease. The other 5% of cases are caused by a rare mutation, and must be identified through further testing. A muscle biopsy may be performed to identify any nerve deterioration, and electromyography (EMG) will test how well the nerves are controlling the muscles.

When diagnosed, SMA is classified into 1 of several types:

Type I SMA (Werdnig–Hoffmann Disease). Type I SMA is the most frequently diagnosed and most severe form of SMA. The disease is apparent at birth or in the first 6 months of life, and the child never learns rolling or independent sitting. The child has severe, generalized muscle weakness, and low muscle tone (hypotonia). Infants typically have muscle wasting (atrophy), weakness in the head and neck, arms, legs, and trunk, and decreased movement. Involuntary movements of the tongue and tremors in the hand may be seen. The child may develop respiratory infections.

Type II SMA (Intermediate Form). In Type II SMA, the disease develops between the ages of 6 months and 18 months, and causes less severe weakness than Type I SMA. Children with Type II SMA are able to learn to sit up and to stand, but usually are not able to walk independently without braces and assistive devices, such as walkers or crutches. Tongue movements and hand tremors may be seen, but are less apparent than in Type I SMA. Contractures (tightening) of joints and scoliosis are common. Respiratory infections and complications occur as the disease progresses, and the need for help with breathing is common in the later stages of the disease.

Type III SMA (Kugelberg–Welander Disease). Type III SMA has a later onset and better prognosis. Type III SMA is usually diagnosed between the ages of 18 months and 3 years, or even later in mild cases, where weakness is not noticeable until late childhood. Children are able to achieve developmental milestones and independent walking, and often they maintain walking until adolescence or adulthood. Walking may be characterized by a lack of balance, frequent falls, scoliosis, knee extension that is more than usual and causes the knee to “bend backward” slightly, and excessive waddling. The muscle weakness mainly affects the muscles around the hips, and is less severe than in Types I and II.

Rare SMAs

Other forms of SMA are rare and are caused by different genes than the SMN1 gene. These forms of SMA include distal spinal muscular atrophy, Kennedy disease, and other classifications. Your physical therapist will educate you about the rarer forms of the disease.

How Can a Physical Therapist Help?

Evaluation is important for guiding the treatment of a child with SMA. Your physical therapist will conduct a thorough evaluation that includes taking the child’s health history and examining the child’s posture, muscle strength, motor activities that include walking, joint motion, respiratory function, participation with family and friends, and quality of life.

Treatment is important to allow children with SMA to achieve the highest level of independent living and mobility possible, and to prevent or delay the development of complications. Physical therapists work closely with the child and family to develop the most appropriate goals for each child based on functional levels and interests.

Your child’s treatment may include:

Therapeutic Exercises and Strength Training. Physical therapists use different therapeutic exercises to help children with SMA improve and maintain mobility, and prevent or slow the progression of contractures and respiratory failure. Therapeutic exercises may include strengthening and aerobic at levels appropriate for the specific child.

Strengthening Exercises. Your physical therapist can help your child slow any deterioration in muscle strength and prolong your child’s ability to walk. Physical therapists design strengthening exercises to keep children with SMA active and moving. They identify games and fun tasks that can be used during therapy or taught to the family to maintain strength.

Improving Developmental Skills. Your physical therapist will develop strategies to help your child learn developmental skills that will improve:

Head and trunk control
Floor mobility, such as rolling and crawling
Changing positions, such as pulling up to stand
Learning upright positions and skills, such as sitting, standing, and walking
Aquatic Therapy or Hydrotherapy. Some physical therapists specialize in aquatic therapy and use the physical properties of water to provide strength training, walking and balance exercises, and aerobic training, without the risk of fatigue or overworked muscles.

Standing Programs. Standing programs for children who can’t walk are used to maintain muscle flexibility and length, prevent contractures, promote musculoskeletal development, and prevent bone-mineral density loss. Your physical therapist can design standing programs to be used at home or at school, as appropriate.

Management of Respiratory Complications. Physical therapists teach parents and caregivers how to perform chest drainage techniques, and help with coughing and breathing techniques to keep children with SMA breathing well. Your physical therapist will provide chest physical therapy as appropriate, and teach the family some blowing games (like bubbles) to improve breathing.

Management of Contractures. Physical therapists help prevent joint tightness (contractures) and increase flexibility in children with SMA by designing specific programs in range-of-motion exercises, positioning, and regular stretching. Your physical therapist may recommend the use of splints, braces, or standing devices, as appropriate.

Feeding. Physical therapists work closely with speech or occupational therapists to promote healthy feeding in children with SMA. They will help position the child in appropriate head and body postures to allow the most effective feeding.

Management of Scoliosis and Skeletal Deformities. Physical therapists can assist in the prevention or reduction of scoliosis and skeletal deformities by designing specific programs to improve movement, and maintain healthy positioning at all times. They will recommend wheelchair modifications and the use of braces to ensure the safety and health of each individual child, as needed. If a child requires surgery for scoliosis or other joint deformities, intensive preoperative and postoperative physical therapy can help prevent respiratory complications and loss of strength or function.

Assistive Devices. Many children with SMA require adaptive or assistive devices to help them maintain function at some point during the course of the disease, and especially following surgery. Physical therapists work with other rehabilitation specialists to select and modify assistive devices to meet each individual child’s specific needs. Types of assistive devices range from those that position a child for feeding or playing, to motorized wheelchairs.

Can this Injury or Condition be Prevented?

SMA is a genetic disorder that is passed from parent to child. Most people have 2 copies of the SMN1 gene. Individuals who have 1 faulty copy and 1 functioning copy of the gene are called carriers. Carriers do not have SMA, but they may pass the faulty gene on to their children. SMA is an autosomal recessive genetic disorder, which means that generally both parents must pass on the mutation for the child to have SMA. Because the specific mutation that causes SMA has been identified, genetic testing using a simple blood test can identify carriers of SMA. However, most people do not know they are carriers until they have a child with SMA.

Excellent prenatal care is important for all pregnant women. Testing can be performed during the pregnancy to determine if a baby has SMA. Once a child is diagnosed with SMA, physical therapists and other health care professionals can reduce some of the additional complications that occur following birth, such as developmental delay, poor feeding, abnormal postures and scoliosis, loss of joint range of motion, abnormal movement or walking patterns, and respiratory problems.

Real Life Experiences

Jody is a 9-month-old baby girl. Over the past few weeks, her parents began noticing that Jody was rolling over and trying to learn to sit up, but seemed too weak to hold herself up. She seemed weaker than they remembered her siblings being when they were infants, but Jody was still trying to be active.

Last week, Jody’s parents took her to see her pediatrician because she was coughing. Her doctor diagnosed a respiratory infection, and admitted her to the hospital for treatment and further tests.

Jody was diagnosed with Type II SMA while in the hospital. Her doctor immediately formed a team to design her treatment plan, including a hospital physical therapist. The family was referred to Cure SMA, an organization that seeks a cure for SMA and provides support for families of children with SMA. The family received a care packet from Cure SMA that included toys that Jody took to right away. Her physical therapist and occupational therapist made sure the toys were appropriate for Jody, and taught the family positions and activities to encourage her to move about on the floor and play with them.

Jody’s hospital physical therapist started a standing program on a specially designed standing frame, and asked the family to stand Jody for 5 to 10 minutes 3 times a day. She taught them how to encourage Jody to crawl on her hands and knees, and to pull herself up to stand. She also taught the family activities to encourage good, strong breathing, such as blowing bubbles, blowing up balloons, and making a pinwheel spin. They also learned games that promoted a good cough.

When Jody was discharged home, her hospital physical therapist recommended a physical therapy pediatric specialist to provide early intervention services in the home.

Jody’s new pediatric physical therapist continues to work with the family’s team of health care providers to promote her best possible function in the home and community. As Jody continues to develop during her early years of life, her physical therapist will teach her activities like walking, climbing stairs, and running. Her physical therapist will monitor her ongoing development and recommend treatments, exercises, and any needed assistive devices to help her perform at her absolute best, as she explores her world and sets and achieves her goals.

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