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Lead Author(s): 

Marc C. Hochberg, MD
Miriam G. Cisternas, MA

Supporting Author(s): 

Sylvia I. Watkins-Castillo, PhD

Spondyloarthropathy (SpA) refers to a family of inflammatory arthropathies that primarily affect the vertebral column. This group differs from other types of arthritis, especially rheumatoid arthritis, in that, rather than primarily affecting the synovial lining tissue in the joints, it involves the connective tissue where the tendons and ligaments attach to bone (entheses). Furthermore, patients with these disorders usually have negative tests for both rheumatoid factor and antibodies to citrullinated peptides (autoantibodies seen in the majority of patients with RA), often have radiographic involvement of the sacroiliac joints, and may have ocular inflammation (i.e., acute iritis or uveitis). Symptoms are often termed inflammatory back pain which is gradual in onset, worse in the morning and improves with activity. Inflammation can also affect the large joints of the lower extremities, including the knees and ankles. In the spondyloarthropathies, sacroiliac joints can fuse, and new bone can form between vertebrae. This leads to ankylosing and can cause deformity of the spine.  In some patients, the spine can become rigid.  

Among the conditions included in the SpA family, axial spondyloarthritis (formerly known as ankylosing spondylitis [AS]) is the most common and refers to inflammation of the spine or one or more adjacent structures of the vertebrae. AS causes inflammation of the tissues in the spine and the root joints (shoulders and hips) and may be associated with peripheral arthritis. Over time, patients can undergo fusion of the vertebrae, limiting movement. AS has a hereditary component and runs in families. It affects males more than females and can occur at any age. Patients with SpA frequently have a genetic marker called HLA B27. Since HLA B27 occurs commonly in the otherwise healthy population (approximately 8% of the US), it is not used as a specific diagnostic marker. HLA B27 is less common in African Americans.

In addition to AS, the more common diseases in the (SpA) family are:
•    Reactive arthritis (formerly known as Reiter’s syndrome), a reaction to an infection in another part of the body;
•    Psoriatic arthritis, which can occur in people with the skin disease psoriasis; and
•    Enteropathic arthritis/spondylitis, a form of chronic inflammatory arthritis associated with inflammatory bowel diseases such as ulcerative colitis and Crohn’s disease. Enteropathic arthritis may be designated as axial (low back pain to ankylosing¬ spondylitis) or peripheral (joint involvement).

While some patients with psoriatic arthritis have a spondyloarthritis, in others, the involvement is primarily peripheral joints. Psoriatic arthritis can resemble rheumatoid arthritis, but tests for rheumatoid factor and anti-CCP will be negative.

Prevalence of Spondylarthropathies

The prevalence of SpA in the US is difficult to determine as the diseases affect ethnic groups differently. Estimates of prevalence for SpA are 0.01%-2.5%.1,2 Current estimates of prevalence of the more common diseases are:
•    Ankylosing spondylitis, 0.2%-1.7%1,2,3,4
     o    Axial SpA, 0.9%-1.4%2,3,4,5,6
     o    Advanced AS, 0.52%-0.55%2
•    Psoriatic arthritis, 0.1%-0.4%1
•    Reactive arthritis, no estimate found
•    Enteropathic peripheral arthritis, 0.065%1
•    Enteropathic axial arthritis, 0.05%-0.25%.1


Healthcare Utilization


Spondyloarthropathy was diagnosed in about one-half million hospitalizations in 2013, representing 1.6% of hospital discharges for all diagnoses, a higher proportion than prevalence in the population (1.6% of discharges vs 1.0%). No differences were found by sex, race/ethnicity, or geographic region, but aging was a factor in the rate of hospitalizations for SpA. (Table 3A. PDF CSV; Table 3A. PDF CSV; Table 3A. PDF CSV; Table 3A. PDF CSV)

Among those with a SpA diagnosis, hospital discharge rates showed higher mean charges ($60,000 per SpA discharge versus $43,000 for any diagnoses) for a similar mean length of stay (4.6 days versus 4.7 days). Discharges from the hospital to additional care (short-term or home health) was slightly higher for SpA diagnosis (40%) than for all diagnoses discharges (31%). (Reference Table 3A. PDF CSV; Table 3A. PDF CSV)


Ambulatory Care Visits

Spondylarthropathies accounted for 0.7% of all diagnoses ambulatory care visits, an indication that SpA treatment is more likely to involve hospitalization than outpatient visits. Males were slightly more likely (0.8%) to receive ambulatory health care for SpA than females, along with those age 45 to 64 (1.0%)and those living in the South region (0.9%). (Reference Table 3A. PDF CSV; Table 3A. PDF CSV; Table 3A. PDF CSV; Table 3A. PDF CSV)


Economic Burden

Economic burden was not calculated by the BMUS project for the spondyloarthropathies due to sample sizes. One study found cited mean annual direct medical costs for AS of $6,500.7

Several published studies have explored the medication cost of biologics. For AS, biologic cost ranged from $1,200 to $24,200; for PSA ranged $14,200 to $32,000.7,8,9

  • 1. a. b. c. d. e. Reveille JD. Epidemiology of spondyloarthritis in North America. Author manuscript. Am J Med Sci. 2011 Apr; 341(4): 284–286. doi:  10.1097/MAJ.0b013e31820f8c99.
  • 2. a. b. c. d. Carmen Stolwijk, MD, Annelies Boonen, MD, PhD, Associate Professor of Rheumatology,  Astrid van Tubergen, MD, PhD, Rheumatologist, and John D. Reveille, M.D., Professor and Director. Epidemiology of spondyloarthritis. Rheum Dis Clin North Am. 2012 Aug; 38(3): 441–476. doi:  10.1016/j.rdc.2012.09.003. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4470267/ Accessed September 18, 2017.
  • 3. a. b. Strand V, Rao SA, Shillington AC, et al. Prevalence of axial spondyloarthritis in United States rheumatology practices: assessment of SpondyloArthritis International Society criteria versus rheumatology expert clinical diagnosis. Arthritis Care Res (Hoboken). 2013 Aug;65(8):1299-306. doi: 10.1002/acr.21994. https://www.ncbi.nlm.nih.gov/pubmed/23436774 . Accessed September 20, 2017.
  • 4. a. b. Curtis JR, Harrold LR, Asgari MM, et al. Diagnostic prevalence of ankylosing spondylitis using computerized health care data, 1996 to 2009: under recognition in a U S health care setting.  Perm J 2016;20(4):15-151.  http://dx.doi.org/10.7812/TPP/15-151 .
  • 5. Deodhar A, Mease PJ, Reveille JD, et al. Frequency of axial spondyloarthritis diagnosis among patients seen by US rheumatologists for evaluation of chronic back pain. Arthritis Rheumatol 2016;68(7):1669-76. doi: 10.1002/art.39612.
  • 6. American College of Rheumatology. Spondyloarthritis. https://www.rheumatology.org/I-Am-A/Patient-Caregiver/Diseases-Condition... . Accessed Sept 18, 2017.
  • 7. a. b. Greenberg JD, Palmer JB, Li Y, et al. Healthcare resource use and direct costs in patients with ankylosing spondylitis and arthritis in a large US cohort. J Rheumatol 2016;43(1):88-96. Doi: 1 0.3899/jrheum.150540.
  • 8. Chastek B, White J, Van Voorhis D, et. al. A retrospective cohort study comparing utilization and costs of biologic therapies and JAK inhibitor therapy across four common inflammatory indications in adult US managed care patients. Adv Ther 2016;33:626-642.
  • 9. Sauer BC, Teng CC, He T, et al. Treatment patterns and annual biologic costs in US veterans with rheumatic conditions or psoriasis. J Med Econ 2016;19(1):34-43. doi: 10.3111/13696998.2015.1086774.


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