Spinal Muscle Atrophy Clinical Presentation

  • Author: Jose A Herrera-Soto, MD; Chief Editor: Mary Ann E Keenan, MD   more...
 
Updated: Sep 16, 2010
 

History

  • Type I: Most mothers report abnormal inactivity of the fetus in the latter stages of pregnancy. The patient with type I spinal muscle atrophy (spinal muscular atrophy, SMA) is unable to roll over or sit. Progressive clinical deterioration occurs. Death usually occurs from respiratory failure and its complications in patients by age 2 years.
  • Type II: Patients with type II SMA have normal development for the first 4-6 months of life. They may be able to sit independently, but they are never able to walk. They require a wheelchair for locomotion. They have a longer life span than patients with type I SMA. Some patients with type II SMA live into the fifth decade of life.
  • Type III: In patients with type III SMA, the presenting complaint is difficulty climbing stairs or getting up from the floor (due to hip extensor weakness). The life span is nearly normal.[15]
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Physical

  • Physical findings specific for each type of spinal muscle atrophy (spinal muscular atrophy, SMA) are as follows:
    • Type I: Newborns with type I SMA are floppy and inactive. They move the extremities little, if at all. The hips are flexed, abducted, and externally rotated. The knees are flexed. Because the distal musculature is usually spared, the fingers and toes move. Infants cannot control or lift the head. Areflexia is universal.
    • Type II: Patients with type II SMA have head control, and 75% of these patients can sit independently. Muscular weakness is greater in the lower extremities than the upper extremities. Patellar reflex is absent. The young may demonstrate bicipital and triceps tendon reflexes. Tongue fasciculations are present, as are upper extremity tremors. Scoliosis is universal, and most patients develop hip dislocation, either unilateral or bilateral, when younger than 10 years.
    • Type III: These patients walk early in life and maintain their ambulatory capacity into adolescence. Weakness may cause foot drop, and patients have limited endurance. A third of the patients become wheelchair bound as adults (mean age 40 years).
  • Other physical findings associated with SMA are as follows:
    • A long C-shaped thoracolumbar scoliotic curve is present in patients with type II SMA and in half of patients with type III SMA. The curve progresses to a severe and incapacitating deformity if not treated. Thirty percent of patients have kyphotic deformities as well.
    • Pseudohypertrophy of the calf is present, which may confound the diagnosis (ie, with Duchenne muscular dystrophy and Becker muscular dystrophy). Bouwsma reported that this finding was associated with elevated serum creatine kinase (CK).[16] This combination was only observed in males; no females in his series had hypertrophy of the calves.[16]
    • Tongue fasciculations are pathognomonic of SMA (all types), as opposed to all other neuromuscular diseases of infancy. Presence of tongue fasciculations can aid in the diagnosis, as 56% of patients exhibit this symptom.
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Causes

Patients with spinal muscle atrophy (spinal muscular atrophy, SMA) have a homozygous deletion of the telomeric SMN1 (survival motor neuron) gene found in arm 5q (bands q11.2-13.3).[9] This deletion has been demonstrated in up to 98% of patients with SMA. SMN is part of a multiprotein complex required for the biogenesis of small nuclear ribonucleoproteins.[17, 18]SMN1 has been linked to pre-mRNA splicing, spliceosome biogenesis, and the nucleolar protein fibrillarin. The absence or dysfunction of SMN is reflected by an enhanced neuronal death. A heterozygous deletion leads to an asymptomatic carrier state.[19]

A significant increase in nuclear DNA vulnerability was detected in fetuses with SMA at 12-15 weeks' gestational age. It reflected a decrease in the number of anterior horn neurons. This vulnerability is no longer seen in the rest of the prenatal or postnatal period. Abnormal cell morphology was seen only in the postnatal period.[20]

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Contributor Information and Disclosures
Author

Jose A Herrera-Soto, MD  Assistant Program Director of Pediatric Orthopedic Fellowship, Orlando Regional Healthcare

Jose A Herrera-Soto, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, North American Spine Society, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society

Disclosure: Nothing to disclose.

Coauthor(s)

Alvin H Crawford, MD, FACS  Professor of Pediatrics and Orthopedic Surgery, University of Cincinnati College of Medicine; Director, Division of Pediatric Orthopedic Surgery, Department of Orthopedic Surgery, Cincinnati Children's Hospital Medical Center

Alvin H Crawford, MD, FACS is a member of the following medical societies: Ohio State Medical Association and Scoliosis Research Society

Disclosure: Nothing to disclose.

Charles T Mehlman, DO, MPH  Professor of Pediatrics and Pediatric Orthopedic Surgery, Division of Pediatric Orthopedic Surgery, Director, Musculoskeletal Outcomes Research, Cincinnati Children's Hospital Medical Center

Charles T Mehlman, DO, MPH is a member of the following medical societies: American Academy of Pediatrics, American Fracture Association, American Medical Association, American Orthopaedic Foot and Ankle Society, American Osteopathic Association, Arthroscopy Association of North America, North American Spine Society, Ohio State Medical Association, Pediatric Orthopaedic Society of North America, and Scoliosis Research Society

Disclosure: Nothing to disclose.

Specialty Editor Board

James F Kellam, MD  Vice-Chair, Department of Orthopedic Surgery, Director of Orthopedic Trauma and Education, Carolinas Medical Center

James F Kellam, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, Orthopaedic Trauma Association, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Francisco Talavera, PharmD, PhD  Senior Pharmacy Editor, eMedicine

Disclosure: eMedicine Salary Employment

William O Shaffer, MD  Professor, Vice-Chairman and Residency Program Director, Department of Orthopedic Surgery, University of Kentucky at Lexington

William O Shaffer, MD is a member of the following medical societies: American Academy of Orthopaedic Surgeons, American Orthopaedic Association, International Society for the Study of the Lumbar Spine, Kentucky Medical Association, Kentucky Orthopaedic Society, North American Spine Society, Southern Medical Association, and Southern Orthopaedic Association

Disclosure: DePuySpine 1997-2007 (not presently) Royalty Consulting; DePuySpine 2002-2007 (closed) Grant/research funds SacroPelvic Instrumentation Biomechanical Study; DePuyBiologics 2005-2008 (closed) Grant/research funds Healos study just closed; DePuySpine 2009 Consulting fee Design of Offset Modification of Expedium

Dinesh Patel, MD, FACS  Associate Clinical Professor of Orthopedic Surgery, Harvard Medical School; Chief of Arthroscopic Surgery, Department of Orthopedic Surgery, Massachusetts General Hospital

Dinesh Patel, MD, FACS is a member of the following medical societies: American Academy of Orthopaedic Surgeons

Disclosure: Nothing to disclose.

Chief Editor

Mary Ann E Keenan, MD  Professor, Vice Chair for Graduate Medical Education, Department of Orthopedic Surgery, University of Pennsylvania School of Medicine; Chief of Neuro-Orthopedics Program, Department of Orthopedic Surgery, Hospital of the University of Pennsylvania

Mary Ann E Keenan, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Orthopaedic Association, American Orthopaedic Foot and Ankle Society, American Society for Surgery of the Hand, and Orthopaedic Rehabilitation Association

Disclosure: Nothing to disclose.

References

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Spinal muscle atrophy, Werdnig-Hoffman disease. Small muscle fibers within separate muscle fascicles.
Spinal muscle atrophy, Werdnig-Hoffman disease. Marked variation in muscle fiber size as well as a relative increase in associated connective tissue.
Spinal muscle atrophy, Kugelberg-Welander disease. Marked variation in muscle fiber size along with increased perimysial connective tissue.
Spinal muscle atrophy, Kugelberg-Welander disease. Muscle fiber variation with some demonstrating internal nuclei.
Spinal muscle atrophy. At age 4 years, this boy's chest radiograph already reveals the presence of significant 32° left thoracic scoliosis. His diagnosis is type I spinal muscle atrophy (Werdnig-Hoffmann disease). This radiograph captures the lumbar curvature incompletely.
Spinal muscle atrophy. By age 6 years, the child's curve is starting to decompensate. Note the development of a right-sided truncal shift. He now has a 40° thoracic curve and a 60° lumbar curvature.
Spinal muscle atrophy. Spine anteroposterior view. The spinal curvature is progressing. The lumbar curve now is 70° and the thoracic curve is 35°. Note that one can now clearly see that the right hip is dislocated. Also note the marked pelvic obliquity in this patient.
Spinal muscle atrophy. By age 9 years, this patient with type I spinal muscle atrophy now has a thoracic curve of 60° and a lumbar curve of 110°. Note that the patient has a tracheostomy tube and a nasogastric tube as well.
Spinal muscle atrophy. Immediate postoperative anteroposterior radiograph of the patient at age 9 years. The thoracic curve is now at 18° and the lumbar curve is 35°, which represents more than 67% curvature correction.
Spinal muscle atrophy. Immediate postoperative lateral view with good sagittal balance.
Spinal muscle atrophy. Follow-up radiographs in the patient at age 13 years reveal some spinal decompensation. Note the so-called coat hanger appearance of the ribs in the patient's dysplastic right hemithorax.
Spinal muscle atrophy. Anteroposterior radiograph of the pelvis demonstrating right hip dislocation.
Spinal muscle atrophy. Lauenstein lateral view of the hips on the patient with spinal muscle atrophy type I. Note the near universal pelvic dysmorphology (eg, widened obturator foramina) in addition to the dislocated right hip.
 
 
 
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