Axial involvement refers to conditions affecting the central part of the body’s skeletal structure, including the spine, pelvis, and rib cage. Understanding this concept is important as it influences how several health conditions manifest and are managed.
Understanding Axial Involvement
The human body’s skeletal system is divided into two main components: the axial skeleton and the appendicular skeleton. The axial skeleton forms the central axis of the body, consisting of 80 bones that include the skull, the vertebral column (spine), the sacrum, the coccyx, and the thoracic cage (ribs and sternum). This central framework provides support and protection for vital organs like the brain, spinal cord, heart, and lungs.
Axial involvement specifically means that symptoms, inflammation, or damage are present within these core structures. For instance, it can affect the joints that connect the spine to the pelvis, known as the sacroiliac joints.
This type of involvement is distinct from peripheral involvement, which affects the limbs, such as the arms, hands, legs, and feet. The distinction between axial and peripheral involvement is important due to differences in symptom patterns, diagnostic approaches, and targeted treatments.
Conditions Characterized by Axial Involvement
Axial involvement is a key feature in several inflammatory conditions, most notably axial spondyloarthritis (axSpA). AxSpA is a type of inflammatory arthritis that primarily affects the joints in the chest, spine, and pelvis. This condition includes ankylosing spondylitis (AS), where damage to the sacroiliac joints and spine can be seen on X-rays, and non-radiographic axSpA (nr-axSpA), which presents with similar symptoms but without visible damage on standard X-rays, though inflammation may be apparent on MRI.
Individuals with axSpA often experience chronic back pain that lasts for three months or longer, typically starting before the age of 45. This pain is characterized by a gradual onset, worsening at night or during rest, and improving with exercise, often accompanied by morning stiffness. Beyond the spine, axSpA can also cause inflammation in other areas like the hips, shoulders, and ribs, and may involve extra-skeletal manifestations such as fatigue, eye inflammation (uveitis), and digestive issues.
Axial involvement can also occur in other inflammatory conditions, such as psoriatic arthritis (PsA) and inflammatory bowel disease (IBD)-associated arthritis. Many PsA patients experience inflammatory back pain and stiffness. IBD-associated arthritis can also present with axial involvement, including sacroiliitis.
Identifying Axial Involvement
Identifying axial involvement typically begins with a thorough evaluation of a patient’s medical history. A physical examination helps assess spinal mobility, tenderness, and any signs of inflammation in relevant joints.
Blood tests are often used to look for markers of inflammation in the body, such as erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), though these markers may be normal in about half of all cases of axial spondyloarthritis. Another important blood test is for the HLA-B27 genetic marker, which is present in over 90% of people with axial spondyloarthritis, though its presence alone does not confirm the condition.
Imaging studies provide visual evidence of inflammation and structural changes. X-rays of the sacroiliac joints and spine can reveal characteristic bone damage, particularly in ankylosing spondylitis. Magnetic Resonance Imaging (MRI) is more sensitive for detecting early inflammation in the sacroiliac joints and spine, especially in non-radiographic axSpA where X-rays may appear normal.
Approaches to Managing Axial Involvement
Managing conditions with axial involvement involves a combination of non-pharmacological and pharmacological strategies aimed at reducing inflammation, alleviating pain, maintaining mobility, and preventing structural damage. Non-pharmacological approaches are foundational and include regular physical therapy, which helps to improve spinal flexibility and muscle strength. Consistent exercise, including both active and supervised programs, is important for managing symptoms and maintaining physical function. Lifestyle modifications, such as smoking cessation, also play a role in overall well-being.
Pharmacological treatments are tailored to the severity and specific characteristics of the condition. Nonsteroidal anti-inflammatory drugs (NSAIDs) are often the first-line medication, used to control inflammation and relieve pain. If NSAIDs are insufficient, more targeted medications may be used. These include biological disease-modifying antirheumatic drugs (bDMARDs), such as TNF inhibitors and IL-17 inhibitors, which work by blocking specific inflammatory pathways. Targeted synthetic DMARDs, like Janus kinase (JAK) inhibitors, are another class of medication for managing inflammation in these conditions.