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Ankylosing Spondylitis: Differential Diagnoses & Workup

Author: S Craig Humphreys, MD, Orthopedic Spine Surgeon, Department of Orthopedic Surgery, Center for Sports Medicine and Orthopedics
Coauthor(s): Jason C Eck, DO, MS, Assistant Professor, Fellow in Orthopedic Spine Surgery, Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota; Scott D Hodges, DO, Consulting Surgeon, Department of Orthopedic Surgery, Center for Sports Medicine and Orthopedics
Contributor Information and Disclosures

Updated: May 29, 2008

Differential Diagnoses

Congenital Spinal Deformity
Osteoarthritis
Degenerative Disk Disease
Osteofibrous Dysplasia
Diffuse Idiopathic Skeletal Hyperostosis
Rheumatoid Spondylitis
Herniated Nucleus Pulposus
Spinal Stenosis
Heterotopic Ossification
Spondylolisthesis, Spondylolysis, and Spondylosis
Kyphosis
Thoracic Spine Fractures and Dislocations
Lower Cervical Spine Fractures and Dislocations
Lumbar Spine Fractures and Dislocations

Workup

Laboratory Studies

  • The diagnosis of AS is not dependent on laboratory data.
  • Elevated erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) are found in approximately 75% of patients and are used as markers of disease activity and response to treatment.18,19
  • Other laboratory values, including alkaline phosphatase (ALP) and creatine kinase (CK), may be elevated; however, these values are generally not used to assess disease activity.
  • Although HLA-B27 is present in most patients with AS, its presence is not necessary to establish the diagnosis.
  • Another marker that is under investigation is mean platelet volume (MPV). Kisacek et al noted that MPV is significantly lower in patients with AS and rheumatoid arthritis relative to control subjects.20 In addition, after therapy, the MPV values increased significantly for both of these conditions. More studies are needed regarding the possible use of MPV as an inflammatory marker in AS and rheumatoid arthritis.

Imaging Studies

  • Radiographs
    • Radiographic evidence of inflammatory changes both in the SI joints and in the spine are useful in the diagnosis and ongoing evaluation of the disease process.21
    • Involvement of the SI joint is a requirement for the diagnosis of AS. Sacroiliitis is a bilateral inflammatory condition leading to bony erosions and sclerosis of the joints (see Image 3).
    • Involvement of the spine is observed radiographically with squaring of the vertebral bodies and ossification of the anulus fibrosus, leading to bridging or syndesmophytes (see Images 4-7). This disease generally begins in the distal portions of the spine and progresses more proximally with time.
    • Plain radiographs of the peripheral skeleton can demonstrate inflammatory changes in some patients, including loss of joint spaces, sclerosis, and deformation (see Image 8).
  • Magnetic resonance imaging (MRI)
    • In most patients, plain radiographs are sufficient to visualize and track the disease progression. However, MRI can be used as an adjunct to evaluate the inflammatory changes and to assess neural compromise (see Image 9).
    • Immediately perform MRI on patients who develop bowel or bladder dysfunction to assess for possible cauda equina syndrome secondary to spinal stenosis (see Treatment, Surgical care).
  • Computed tomography (CT) scans may be useful in patients with suspected spinal fracture who have equivocal radiographs.

Other Tests

  • The diagnosis of AS generally is based on clinical presentation.
  • The New York Criteria for the diagnosis of AS, which is based on clinical and radiographic findings, are as follows:
    • Limitation of motion of the lumbar spine in all 3 planes
    • History of pain or presence of pain at the thoracolumbar junction or in the lumbar spine
    • Limitation of chest expansion to 1 inch or less, as measured at the fourth intercostal space
  • Radiographic SI changes are as follows:
    • Grade 0 – Normal
    • Grade 1 – Suspicious
    • Grade 2 – Minimal sacroiliitis
    • Grade 3 – Moderate sacroiliitis
    • Grade 4 – Ankylosis
  • A definite diagnosis of AS is met if there is (1) grade 3-4 bilateral sacroiliitis with at least 1 clinical criterion or (2) grade 3-4 unilateral sacroiliitis or grade 2 bilateral sacroiliitis with clinical criterion 1 or with both clinical criteria 2 and 3. A probable diagnosis of AS is made if a grade 3-4 bilateral sacroiliitis exists without any signs or symptoms that satisfy the clinical criteria.
  • As noted in the New York Criteria above, radiographic evidence of SI changes is graded from a normal SI joint (grade 0) to evidence of complete ankylosis (grade 4). The disease progression is a gradual process, and the grading is somewhat subjective.

Histologic Findings

Early AS lesions include subchondral granulation tissue that erodes the joint and is replaced gradually by fibrocartilage followed by ossification.

Biopsy and histologic analysis are not indicated for individuals with AS.

More on Ankylosing Spondylitis

Overview: Ankylosing Spondylitis
Differential Diagnoses & Workup: Ankylosing Spondylitis
Treatment & Medication: Ankylosing Spondylitis
Follow-up: Ankylosing Spondylitis
Multimedia: Ankylosing Spondylitis
References
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Further Reading

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Keywords

AS, Marie-Strumpell disease, von Bechterew disease, rheumatoid spondylitis, seronegative spondyloarthropathy, reactive arthritis, psoriasis, juvenile-onset spondylitis, juvenile chronic arthritis, ulcerative colitis, Crohn disease, Crohn's disease, human leukocyte antigen B27, HLA-B27, spondylodiscitis, Andersson lesions, anulus fibrosus

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Contributor Information and Disclosures

Author

S Craig Humphreys, MD, Orthopedic Spine Surgeon, Department of Orthopedic Surgery, Center for Sports Medicine and Orthopedics
S Craig Humphreys, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Orthopaedic Surgeons, American Medical Association, American Spinal Injury Association, North American Spine Society, Southern Medical Association, Southern Orthopaedic Association, and Tennessee Medical Association
Disclosure: Nothing to disclose.

Coauthor(s)

Jason C Eck, DO, MS, Assistant Professor, Fellow in Orthopedic Spine Surgery, Department of Orthopedic Surgery, Mayo Clinic, Rochester, Minnesota
Jason C Eck, DO, MS is a member of the following medical societies: American Osteopathic Academy of Orthopedics, American Osteopathic Association, and North American Spine Society
Disclosure: Nothing to disclose.

Scott D Hodges, DO, Consulting Surgeon, Department of Orthopedic Surgery, Center for Sports Medicine and Orthopedics
Scott D Hodges, DO is a member of the following medical societies: American Academy of Disability Evaluating Physicians, American Medical Association, American Osteopathic Association, American Spinal Injury Association, North American Spine Society, Southern Medical Association, Southern Orthopaedic Association, and Tennessee Medical Association
Disclosure: Medtronic Royalty Consulting; Biomet Spine Royalty Consulting

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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