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A.D.A.M. Medical Encyclopedia [Internet]. Atlanta (GA): A.D.A.M.; 2013.

A.D.A.M. Medical Encyclopedia.

Spinal muscular atrophy

Werdnig-Hoffmann disease; Kugelberg Welander

Last reviewed: February 10, 2014.

Spinal muscular atrophy is a group of disorders of the motor neurons (motor cells). These disorders are inherited and can appear at any stage of life. The disorder leads to muscle weakness and atrophy.

Causes

Spinal muscular atrophy (SMA) is a collection of different muscle diseases. Grouped together, it is the second leading cause of hereditary neuromuscular disease, after Duchenne muscular dystrophy.

Most of the time, a person must get the defective gene from both parents to be affected. About 4 out of every 100,000 people have the condition.

The most severe form is SMA type I, also called Werdnig-Hoffman disease. Infants with SMA type II have less severe symptoms during early infancy, but they become weaker with time. SMA type III is the least severe form of the disease.

Rarely, SMA may begin in adulthood. This is usually a milder form of the disease.

A family history of spinal muscular atrophy is a risk factor for all types of the disorder.

Symptoms

  • Infants with SMA type I are born with very little muscle tone, weak muscles, and feeding and breathing problems.
  • With SMA type II, symptoms may not appear until age 6 months to 2 years.
  • Type III SMA is a milder disease that starts in childhood or adolescence and slowly gets worse.
  • Type IV is even milder, with weakness starting in adulthood.

Often, weakness is first felt in the shoulder and leg muscles. Weakness gets worse over time and eventually becomes severe.

Symptoms in an infant:

  • Breathing difficulty, leading to a lack of oxygen
  • Feeding difficulty (food may go into the windpipe instead of the stomach)
  • Floppy infant (poor muscle tone)
  • Lack of head control
  • Little movement
  • Weakness that gets worse

Symptoms in a child:

  • Frequent, increasingly severe respiratory infections
  • Nasal speech
  • Posture that gets worse

Exams and Tests

The health care provider will take a careful history and perform a brain/nervous system (neurologic) examination to find out if there is:

Tests:

Treatment

There is no treatment for the weakness caused by the disease. Supportive care is important. Attention must be paid to the respiratory system because affected people have trouble protecting themselves from choking. Breathing complications are common. Breathing can be assisted with invasive or noninvasive devices.

Physical therapy is important to prevent contractions of muscles and tendons and abnormal curvature of the spine (scoliosis). Bracing may be needed. Surgery may be needed to correct skeletal deformities, such as scoliosis.

Outlook (Prognosis)

People with SMA type I rarely live longer than 2 - 3 years because of respiratory problems and infections. Survival time with type II is longer, but the disease kills most of those who are affected while they are still children.

Children with type III disease may survive into early adulthood. However, people with all forms of the disease have weakness and debility that gets worse over time. Adults who develop SMA often have a normal life expectancy.

Possible Complications

When to Contact a Medical Professional

Call your health care provider if your child:

  • Appears weak
  • Develops any other symptoms of spinal muscular atrophy
  • Has difficulty feeding

Breathing difficulty can rapidly become an emergency condition.

Prevention

Genetic counseling is recommended for people with a family history of spinal muscular atrophy who want to have children.

References

  1. Sarnat HB. Spinal muscular atrophies. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF. Nelson Textbook of Pediatrics. 19th ed. Philadelphia, Pa: Elsevier; 2011:chap 604.2.

Review Date: 2/10/2014.

Reviewed by: Joseph V. Campellone, M.D., Division of Neurology, Cooper University Hospital, Camden, NJ. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.

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Copyright © 2013, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org). URAC's accreditation program is an independent audit to verify that A.D.A.M. follows rigorous standards of quality and accountability. A.D.A.M. is among the first to achieve this important distinction for online health information and services. Learn more about A.D.A.M.'s editorial policy, editorial process and privacy policy. A.D.A.M. is also a founding member of Hi-Ethics and subscribes to the principles of the Health on the Net Foundation (www.hon.ch).

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only — they do not constitute endorsementscof those other sites. © 1997–2011 A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.

Copyright © 2013, A.D.A.M., Inc.

What works?

  • Drug treatment for spinal muscular atrophy type IDrug treatment for spinal muscular atrophy type I
    Spinal muscular atrophy (SMA) is a severe neuromuscular disease with onset in childhood and adolescence that results in progressive muscle weakness. There are three main types of SMA. Drug treatment for SMA types II and III is discussed in a separate Cochrane review. The age of onset of SMA type I, also known as Werdnig‐Hoffmann disease, is before six months. Children with SMA type I will never be able to sit without support and usually die by the age of two years. It is one of the most important causes of death due to a genetic disease in childhood. There was only one small randomised trial in the original review, which assessed the efficacy of riluzole for 10 children with SMA type I. In this trial all three children in the placebo group died, but three of the seven children treated with riluzole were still alive at the ages of 30, 48 and 64 months. However, none of the children in the riluzole or placebo group developed the ability to roll, sit or stand. For several reasons the overall quality of the study was low, mainly because the study was too small to detect an effect and there were baseline differences that resulted in risk of bias. Evidence is insufficient to recommend riluzole for SMA type I. No further trials were identified for this 2011 update. No drug treatment has been shown to have significant efficacy for SMA type I.
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  • Superficial anterior muscles.

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