Ankylosing Spondylitis
Spondyloarthritis is a term derived from two Greek words: "spondylos" (vertebra) and "arthrom" (joint), followed by the Latin suffix "itis" (inflammation). It refers to a group of chronic diseases, whose causes are not fully understood, that share common features, one of which is the inflammatory process involving the joints of the spine and those that connect it to the pelvis (sacroiliac joints). The prototypical disease is Ankylosing Spondylitis (AS).
Within the family of spondyloarthritis, in addition to ankylosing spondylitis, we can mention psoriatic arthritis, enteropathic arthropathies (associated with inflammatory bowel diseases such as Crohn's disease and ulcerative colitis), reactive arthritis, juvenile spondyloarthritis, and undifferentiated spondyloarthritis.
All spondyloarthritis is a systemic disease, meaning that in addition to the musculoskeletal system, it can affect other organs, systems, and apparatuses (eyes, digestive tract, respiratory system, heart, etc.). Rheumatology is the medical specialty that primarily focuses on the treatment of these musculoskeletal conditions.
Ankylosing spondylitis is the prototypical spondyloarthritis and the one that most frequently affects the joints of the spine and sacroiliac joints, known as axial joints, as opposed to the joints of the extremities (hips, knees, ankles, elbows, etc.), which are collectively called peripheral joints. Its cause is unknown, but there is a genetic predisposition, primarily due to the presence of the HLA-B27 gene, which increases the likelihood of developing the disease approximately 100-fold. In the last decade, other genes that contribute to this predisposition have been identified.
Ankylosing spondylitis is definitively diagnosed based on symptoms, physical examination, and imaging findings. The diagnostic criteria for definitively classifying a patient as having ankylosing spondylitis require the presence of radiographically visible erosions in the sacroiliac joints.
New imaging techniques, more sensitive than X-rays, especially magnetic resonance imaging (MRI), led to the emergence in 2010 of new criteria associated with a change in nomenclature: axial spondyloarthritis. All ankylosing spondylitis is axial spondyloarthritis, but not all axial spondyloarthritis meets the criteria to be classified as ankylosing spondylitis.
In 2010, an ASAS consensus conference was held. Table 1 presents the new criteria for the diagnosis of axial spondyloarthritis, which allow for faster detection of this type of condition. These criteria were designed for patients under 45 years of age who present with low back pain of three months or more.
Axial spondyloarthritis is a type of spondyloarthritis that predominantly affects the joints of the spine and sacroiliac joints (axial joints), causing inflammatory pain and stiffness. Lower back and lumbosacral pain are the most common, and most patients are young (under 45 years of age). Highly sensitive imaging techniques, such as magnetic resonance imaging (MRI), can identify this inflammatory process early, years before it becomes visible on plain radiographs. During this period, when lesions are not identified on plain radiographs but are detected by more sensitive techniques, it is referred to as non-radiographic axial spondyloarthritis. When radiographic lesions are present in the sacroiliac joints, at stage II (bilateral) or III or IV (unilateral or bilateral), a diagnosis of ankylosing spondylitis is established. The objective, obviously, is to diagnose and treat spondyloarthritis in the non-radiographic phase, avoiding sequelae in the locomotor system and achieving the best quality of life for the patient.
Ankylosing spondylitis is the prototypical radiographic spondyloarthritis, whose main symptoms are inflammatory lower back pain, sometimes radiating to the buttocks and posterolateral aspect of the thigh, and stiffness: difficulty bending forward or to the sides, especially after periods of immobilization and in the mornings. The areas where ligaments and tendons attach to bone, that is, the entheses, also participate in the inflammatory process, particularly in the lower extremities. Thus, Achilles tendinitis and plantar fasciitis are common, causing pain in the back of the foot. Forty percent of patients may experience inflammation of the inner layer of the eye (uveitis) during the course of the disease, especially in its anterior portion (iridocyclitis), which usually presents as acute attacks.
There are no comprehensive epidemiological studies regarding axial spondyloarthritis, but it is worth considering that, in both its non-radiographic and radiographic forms (which includes ankylosing spondylitis), 3-10 out of every 1000 people would be affected.
Recently, the term pre-spondyloarthritis has been introduced to designate supposedly healthy relatives of patients with ankylosing spondylitis who meet ASAS diagnostic criteria for spondyloarthritis or European Spondyloarthropathy Study Group (ESSG) criteria or both.