What are spondyloarthropathies?

What are Spondyloarthropathies?

Spondyloarthropathies are a group of chronic inflammatory rheumatic diseases that primarily affect the axial skeleton (spine and sacroiliac joints), characterized by inflammatory back pain, sacroiliitis, and a strong association with HLA-B27, while lacking rheumatoid factor (hence "seronegative"). 1

Disease Spectrum

Spondyloarthropathies encompass several distinct but related conditions that share common clinical and genetic features 1, 2:

• Ankylosing spondylitis (AS) - the prototypical form with radiographic sacroiliitis 1
• Reactive arthritis (including Reiter's syndrome) 2, 3
• Psoriatic arthritis with axial involvement 1, 2
• Enteropathic arthritis associated with inflammatory bowel disease 2, 3
• Juvenile spondyloarthropathy 2, 3
• Undifferentiated spondyloarthropathy 2, 4
• Non-radiographic axial spondyloarthritis - patients without visible radiographic damage but with inflammatory changes on MRI 1

Core Clinical Features

Inflammatory Back Pain

The hallmark symptom present in 70-80% of patients includes specific characteristics 5, 1:

• Onset before age 40-45 years with insidious (not traumatic) beginning 5, 1
• Chronic duration of at least 3 months 1, 5
• Morning stiffness that is prolonged 5
• Improvement with exercise but not with rest - a key distinguishing feature 5, 1
• Night pain, particularly awakening in the second half of the night 5, 1
• Alternating buttock pain indicating sacroiliac joint involvement 5, 1

Musculoskeletal Manifestations

The disease follows a characteristic pattern of involvement 1, 5:

• Sacroiliac joints are typically the initial site, presenting as lower back/buttock pain 5
• Spinal involvement progresses to affect the thoracic spine and thoracolumbar junction most commonly 5, 1
• Peripheral arthritis occurs in 30-50% of patients, affecting large joints (especially knees) in an oligoarticular, asymmetric pattern 5
• Enthesitis - inflammation at tendon and ligament insertion sites 2, 6
• Dactylitis (sausage digits) may occur 7

Extra-Articular Manifestations

These conditions extend beyond the joints 1, 5:

• Acute anterior uveitis occurs in up to 40% of patients 1, 5
• Psoriasis 5, 1
• Inflammatory bowel disease 5, 1
• Aortic root involvement and aortic valve regurgitation in up to 80% of patients with ankylosing spondylitis 1

Genetic and Laboratory Features

HLA-B27 Association

The genetic component is strong but not diagnostic alone 1, 5:

• HLA-B27 positivity is present in 74-89% of patients with axial spondyloarthritis 5, 1
• The association varies among different spondyloarthropathy subtypes and ethnic groups 7
• Environmental factors appear to trigger disease in genetically predisposed individuals 7

Laboratory Findings

Serologic markers help distinguish these conditions 6, 4:

• Absence of rheumatoid factor (hence "seronegative" spondyloarthropathies) 1, 6, 3
• Elevated C-reactive protein may be present but is not always elevated 5, 1
• Anemia of chronic inflammation may occur 6

Diagnostic Challenges

Delayed Recognition

A critical clinical pitfall is the substantial diagnostic delay 5, 1:

• Mean delay of 4.9 to 8 years from symptom onset to diagnosis has been reported 5
• Inflammatory back pain symptoms are present in 5-6% of the general adult population and up to 15% in primary care settings, so additional features beyond back pain alone are needed 5, 1

Imaging Evolution

The diagnostic approach has evolved significantly 1:

• Conventional radiography remains the first-line imaging modality but has low sensitivity for early disease, with radiographic findings often lagging 7 or more years behind symptom onset 1
• MRI of sacroiliac joints is now included in modern classification criteria for detecting "preradiographic" disease through identification of bone marrow edema and inflammatory changes 1
• CT may be helpful when MRI is contraindicated, showing subtle erosions and structural changes 1

Disease Progression and Impact

The natural history involves progressive structural damage 1:

• Chronic back pain and stiffness leading to progressive loss of spinal mobility 5
• Syndesmophyte formation and eventual spinal ankylosis in advanced cases 2
• Substantial physical and social burdens, interfering with work and schooling 1
• Loss of mobility and function when diagnosis and treatment are delayed 1

Clinical Pearls

Early recognition is critical because effective biologic therapies (particularly TNF-α antagonists) can arrest disease progression and prevent disability, but only if initiated before irreversible radiographic joint damage occurs 1. The prevalence of axial spondyloarthritis is estimated at 0.9-1.4% in the US adult population, making it more common than previously recognized 1.