eMedicine Specialties > Orthopedic Surgery > Spine

Spinal Muscle Atrophy: Differential Diagnoses & Workup

Author: Jose A Herrera-Soto, MD, Assistant Program Director of Pediatric Orthopedic Fellowship, Orlando Regional Healthcare
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; Charles T Mehlman, DO, MPH, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, Cincinnati Children's Hospital Medical Center
Contributor Information and Disclosures

Updated: Aug 21, 2008

Differential Diagnoses

Muscular Dystrophy

Other Problems to Be Considered

Cerebral palsy (hypotonic diplegia)
Congenital muscular dystrophy
Transverse myelitis
Juvenile myasthenia gravis
Progressive muscular dystrophy
Polymyositis
Benign congenital hypotonia
Multifocal motor neuropathy
Chronic inflammatory demyelinated polyneuropathy
Inflammatory myopathy
Congenital heart disease21

Workup

Laboratory Studies

  • Aldolase and serum CK findings are within reference ranges in patients with spinal muscle atrophy (spinal muscular atrophy, SMA), as opposed to findings in patients with Duchenne muscular dystrophy and Becker muscular dystrophy. In later-onset SMA, these muscle enzymes may be slightly elevated.

Imaging Studies

  • Pelvis anteroposterior (AP) and lateral views: Most patients with type II spinal muscle atrophy (spinal muscular atrophy, SMA) develop hip dislocations. The dislocations are only temporarily symptomatic and do not influence function in these patients because they are nonambulatory.
  • Complete spine and scoliosis series: All patients with type II SMA and most patients with type III SMA develop a long C-shaped scoliotic curve (see Image 5, Image 6, Image 7, Image 8, Image 9, Image 10, Image 11, Image 12, Image 13).

Other Tests

  • Electromyograms and nerve conduction studies: Electromyogram findings in patients with spinal muscle atrophy (spinal muscular atrophy, SMA) are characteristic of a neuropathic disorder; they reveal fibrillation potentials, denervation, and increased amplitude. However, nerve conduction velocity test results are normal.
  • Prenatal DNA testing: Prenatal DNA analysis is available to diagnose the deletion of arm 5q.

Procedures

  • Incisional biopsy: Muscle biopsies reveal a uniform smaller diameter of all fibers in patients with spinal muscle atrophy (spinal muscular atrophy, SMA). This contrasts with biopsy findings for other muscular dystrophies, which consist of degenerating muscle with variable muscle fiber sizes. Biopsies in patients with hypotonic cerebral palsy reveal normal muscle fibers.

Histologic Findings

Two subtypes of spinal muscle atrophy (spinal muscular atrophy, SMA) deserve special mention regarding their typical histologic appearance. Werdnig-Hoffmann disease is typically diagnosed in patients from birth to age 6 months. Its histologic pattern is usually one of extremely small and reasonably uniform small muscle fibers (see Image 1, Image 2). In the Kugelberg-Welander type of SMA (usually diagnosed in patients aged 2-15 y), the same tendency toward small muscle fiber diameter is seen but with much less uniformity (see Image 3, Image 4). Substantial variation, with intermixing of larger and smaller muscle fibers, may be observed.

In both forms of the disease, substantial increases in muscular connective tissue lead to both characteristic histologic findings (see Image 2, Image 3) and clinical findings such as increased muscle firmness. Centrally migrated or otherwise internalized nuclei are considered pathologic if they are present in more than about 3% of muscle fibers. Such nuclear findings are common in a variety of muscle diseases, including SMA.

(Also see Procedures, above).

More on Spinal Muscle Atrophy

Overview: Spinal Muscle Atrophy
Differential Diagnoses & Workup: Spinal Muscle Atrophy
Treatment & Medication: Spinal Muscle Atrophy
Follow-up: Spinal Muscle Atrophy
Multimedia: Spinal Muscle Atrophy
References
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References

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  4. Herring JA. Disorders of the spinal cord. In: Tachdjian Pediatric Orthopaedics. vol 2. Philadelphia, Pa: WB Saunders Co; 2002:1311-1319.

  5. Werdnig G. Ueber einem Fall von Dystrophiae musculorum mit positivenen Ruckenmakefunde. Wien me Wchnschr. 1890;40:1798.

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Further Reading

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Keywords

spinal muscle atrophy, spinal muscular atrophy, SMA, muscle atrophy, muscular atrophy, Werdnig-Hoffmann disease, Werdnig-Hoffmann, Werdnig Hoffmann, Kugelberg-Welander disease, Kugelberg-Welander, Kugelberg Welander, hypotonia, muscle weakness, spinal fusion, spinal muscular atrophies of childhood, spinal muscular atrophy of childhood, spinal cord disease, spinal infantile muscular atrophy, spinal infantile muscle atrophy

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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, Director, Musculoskeletal Outcomes Research, Associate Professor, Division of Pediatric Orthopedic Surgery, 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.

Medical Editor

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.

Pharmacy Editor

Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine
Disclosure: Nothing to disclose.

Managing Editor

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

CME Editor

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, American Association of Physicians of Indian Origin, American College of International Physicians, and American College of 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.

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