- Spinal Muscular Atrophy Types
- Spinal Muscular Atrophy Symptoms
- Life Expectancy
Spinal muscular atrophy (SMA) is a group of inherited diseases that attack and destroy motor neurons, which are the nerve cells in the brain stem and spinal cord that control muscles.
Some symptoms of SMA can be painful, such as:
Pain may be worsened by activities such as transferring the patient from bed to wheelchair.
Secondary conditions that may be associated with SMA that can also cause pain include:
- Gastrointestinal symptoms that may cause pain include: gastroesophageal reflux disease, erosive esophagitis, and constipation
- Orthopedic symptoms that may cause pain include: hip dislocation, osteoporosis with spinal compression fractures, tendon retractions, and weight-bearing pain
- Neurological symptoms that may cause pain include: acute or chronic post-surgical pain
- Urological symptoms that may cause pain include: catheterization trauma
- Respiratory symptoms that may cause pain include: bronchiolitis and hypoxia
What Are the Types of Spinal Muscular Atrophy?
There are four types of spinal muscular atrophy:
- SMA type I (also called Werdnig-Hoffmann disease or infantile-onset SMA)
- Usually present before 6 months of age
- The most severely affected infants have reduced movements in utero and are born with limited joint movement (contractures) and breathing difficulties
- Patients may die in the first year of life without treatment
- SMA type II (also called Dubowitz disease or intermediate SMA)
- First symptoms usually show between 6 and 18 months of age although some can present earlier
- Accounts for about 20% of all cases of SMA
- Babies can sit without support but cannot stand or walk unaided, and without treatment, over time, some may lose the ability to remain independently seated
- SMA type III (also called mild SMA, juvenile onset, or Kugelberg-Welander disease)
- SMA type IV (late-onset SMA)
- Symptoms develop after 21 years of age
What Are Symptoms of Spinal Muscular Atrophy?
Symptoms of spinal muscular atrophy (SMA) vary in severity depending on the type.
Symptoms of SMA type I include:
- Reduced muscle tone (hypotonia)
- Severe weakness
- Diminished limb movements
- Lack of tendon reflexes
- Muscle twitching (fasciculations)
- Swallowing and feeding difficulties
- Difficulty breathing
- Newborns don’t achieve any motor milestones
- Facial paralysis
- Lack of reaction to stimuli
- Congenital heart defect
- Scoliosis or other skeletal abnormalities may develop as children get older
Symptoms of SMA type II include:
- Muscle weakness close to the center of the body
- Weakness involves the lower limbs more than the upper limbs
- Tremor in the hands
- Limited joint movement (contractures)
- Respiratory complications
Symptoms of SMA type III include:
- Foot deformities
- Respiratory muscle weakness
Symptoms of SMA type IV include:
- Muscles closer to the center of the body (proximal muscles) usually are more affected
- Legs tend to weaken before the arms
- Hands may weaken eventually, but they usually remain strong enough for typing on a computer keyboard and other basic functions
What Causes Spinal Muscular Atrophy?
The most common form of spinal muscular atrophy (SMA) is caused by genetic defects in both copies of the survival motor neuron 1 gene (SMN1) on chromosome 5q. Except in rare cases, the patient inherits one mutated gene from each parent.
Less common forms of SMA are caused by mutations in other genes.
How Is Spinal Muscular Atrophy Diagnosed?
Spinal muscular atrophy (SMA) is diagnosed with a patient history and physical examination, and a blood test to look for deletions or mutations of the SMN1 gene.
Other tests used to diagnose SMA include:
- Electromyography (records the electrical activity of the muscles during contraction and at rest)
- Nerve conduction velocity studies (measures the nerve’s ability to send an electrical signal)
- Muscle biopsy
- Other blood tests
What Is the Treatment for Spinal Muscular Atrophy?
There is no cure for spinal muscular atrophy (SMA), and treatment is aimed at managing symptoms and preventing complications.
Medications used to treat SMA include:
- Nusinersen (Spinraza) to treat children and adults with SMA
- Onasemnogene abeparovec-xioi (Zolgensma) gene therapy for children under 2 years old
- Rrisdiplam (Evrysdi) to treat patients age two months of age and older
Other treatments for SMA include:
- Physical therapy
- Occupational therapy
- Stretching and strengthening exercises
- Speech and swallowing therapy
- Assistive devices such as supports or braces, orthotics, speech synthesizers, and wheelchairs
- Proper nutrition and calories
- Feeding tube
- Non-invasive ventilation at night
- Assisted ventilation during the day
What Are Complications of Spinal Muscular Atrophy?
Complications of spinal muscular atrophy (SMA) include:
- Severe weakness
- Heart defects
- Respiratory failure
- Foot deformities
What Is the Life Expectancy for Spinal Muscular Atrophy?
The life expectancy varies depending on the type spinal muscular atrophy (SMA).
- Without treatment, children with SMA type 1 never sit or stand and the majority die of respiratory failure before the age of 2 years
- Children with SMA type II have a reduced life expectancy, but most live into adolescence or young adulthood
- People with SMA type III may be prone to respiratory infections, but with proper care most will have a normal lifespan
- People with SMA type IV that comes on in the late teens or adulthood generally have a normal lifespan
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