How to Diagnose Spinal Muscular Atrophy

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Spinal muscular atrophy (SMA) is a genetic condition that causes weak muscles and decreased mobility. It’s a lifelong condition, but it’s manageable with modern medicine. The first step is diagnosing the condition. Since it usually appears in babies, this can be tricky, but with careful observation, you can spot the signs and have your baby tested. Then you can start treatment to improve the condition.

Things You Should Know

• In babies, look for signs of spinal muscular atrophy (SMA) by watching for things like a lack of head or arm movement, heavy or rapid breathing, and not meeting milestones for rolling or crawling.
• You may also notice that your baby's back is smaller than normal, which will continue to become more obvious with time.
• The weakened muscles in your baby's back may also lead them to have a curved spine, or scoliosis.
• You can ask your doctor to test your baby for SMA as a newborn, but in many places, this testing is done automatically.
• SMA can sometimes appear later in life, but when that happens, it's usually a milder case than it is when it presents in newborns.

Steps

Method 1

Method 1 of 2:

Symptoms

1. 
   1
   Increasing muscle weakness: SMA prevents muscles from responding to nerve signals, causing the muscles to weaken over time. This gradual weakening is the main first sign of the condition.

   • If your child is an infant, they won’t be able to communicate their symptoms to you, so you’ll have to look for other signs of muscle weakness. These include lack of arm or head movement, heavy breathing, and inability to roll or crawl.
   • It’s rare, but SMA can start later in life, usually around age 20. These cases are usually more mild, but can still cause quality of life issues. An adult will notice a sudden, progressive muscle weakness as the first symptom.
2. 
   2
   Lack of kicking, waving, or arm-raising: With weaker muscles, your baby won’t be able to move their arms or legs very well. If they don’t kick much or reach out, then this could be an SMA sign.

   • Babies can usually make smooth arm and leg movements around 2 months, so this is an early developmental milestone. Definitely see your pediatrician if your baby doesn't seem to be moving properly.
3. 
   3
   Lack of head movement: SMA also affects and weakens the neck muscles. Your baby may not be able to move their head side to side to look around, or lift their head on their own.

   • Babies should be able to hold their heads up at around 2 months old. If your baby is having trouble holding their head up and they’re older than this, it’s a cause for concern.
4. 
   4
   Rapid breathing: SMA could affect your child’s chest muscles, making breathing more difficult and rapid. You may notice more movement in your baby’s belly than chest.

   • People with SMA may need a breathing device at night to help them sleep and prevent sleep apnea.
5. 
   5
   Trouble rolling or sitting up: Babies with SMA are often described as “floppy,” meaning they can’t straighten themselves out. Since their muscles are weaker, they won’t be able to sit or roll normally.

   • Babies normally learn to roll around 4 months old, and can sit around 6 months. If your baby doesn’t hit these milestones, it could be an SMA symptom.
6. 
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   Reduced back muscle size: Atrophy means that muscles decline in size, so your child’s back muscles may be visibly smaller than normal. The decline is progressive, so the back muscles will continue shrinking over time.
7. 
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   Scoliosis or spine curvature. With weaker back muscles, the spine may not be able to stay straight. A noticeable curve, also called scoliosis, might develop in your baby’s spine.

   • Scoliosis from SMA can start as early as 8-9 months, but mild cases might not appear until 6-8 years.
8. 
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   Consistent falling or lack of balance: SMA could also develop after your child can already walk. If this happens, you’ll probably notice that they can’t keep their balance or walk straight. They might fall often, even without a noticeable cause.

   • SMA that appears later, around 18 months, is known as type III and is usually a milder form.
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Method 2

Method 2 of 2:

Medical Diagnosis

1. 
   1
   Prenatal testing: Since SMA is passed on genetically, your baby could be at risk if anyone in your family has it. Your doctor might suggest prenatal testing in this case. For this test, the doctor collects fluid or tissue from around the fetus for testing. If the test comes back positive for SMA, you an start planning to care for your baby when they’re born.

   • The SMA test searches for the survival motor neuron 1 (SMN1) gene. If this gene is absent or abnormal, then the SMA test is positive.
   • This test is usually done around 15-20 weeks of pregnancy, but other tests can be done as early as 10 weeks.
2. 
   2
   Newborn screening: Beginning treatment before SMA symptoms appear generally leads to better results, so newborn screening is very important. When your baby is born, ask your doctor to complete the genetic test for SMA, especially if you have a family history of the condition. This way, you can begin treatment early if you have to.

   • The screening is usually a blood test that checks for the SMN1 gene.
   • In some US states, this test is required by law, so your baby may be tested automatically.
   • If you’ve already had prenatal screening for SMA, then your baby might not need it again when they’re born. Ask your doctor what is best.
3. 
   3
   Toddler testing: If your child never had an SMA screening and shows any of the symptoms like muscle weakness, then it’s very important to get them tested. Bring them in for SMA screening and if the test comes back positive.

   • This is the same test that the doctor will run on a newborn. It’s a blood test to check for the SMN1 gene.
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Expert Q&A

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• Question

  How is muscular dystrophy diagnosed?

  

  Kevin Stone, MD
  Board Certified Orthopaedic Surgeon

  Dr. Kevin Stone is an orthopaedic surgeon and the founder of The Stone Clinic, a leading orthopaedic surgery, sports medicine, and rehabilitation clinic in the San Francisco Bay Area. With over 30 years of experience, Dr. Stone specializes in knee, shoulder, and ankle repair, using biologic reconstruction and joint replacement. He holds a BS in Biology from Harvard University and a Doctor of Medicine (MD) from the University of North Carolina at Chapel Hill. Dr. Stone completed his residency in Internal Medicine and Orthopaedic Surgery at Harvard University and in General Surgery at Stanford University. He then completed a fellowship in Orthopaedic Research and Surgery at the Hospital for Special Surgery and Tahoe Orthopaedics. He lectures around the world as an expert in cartilage and meniscal growth, replacement, and repair and holds over 40 U.S. patents on novel inventions to improve healthcare. Dr. Stone is a physician for Smuin Ballet and has served as a physician for the U.S. Ski Team, the U.S. Pro Ski Tour, the United States Olympic Training Center, and World Pro Ski Tour.

  

  Kevin Stone, MD

  Board Certified Orthopaedic Surgeon

  Expert Answer

  Muscular dystrophy is diagnosed mainly through genetic testing. Contact your genetic counselor to set up an appointment.

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Tips

• SMA presents differently in different people, so all the symptoms may not be the same. This is why you need a professional diagnosis.
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