Modified Stoke Ankylosing Spondylitis Spine Score (mSASSS): Understanding Spinal Damage in AS

What is the Modified Stoke Ankylosing Spondylitis Spine Score?

The Modified Stoke Ankylosing Spondylitis Spine Score (mSASSS) is a widely recognized and standardized radiographic scoring system used to quantify structural damage and disease progression in the spine of individuals with Ankylosing Spondylitis (AS).

Understanding Ankylosing Spondylitis and Spinal Assessment

Ankylosing Spondylitis (AS) is a chronic inflammatory disease primarily affecting the spine and sacroiliac (SI) joints. It is characterized by pain, stiffness, and potentially progressive structural damage, leading to fusion of vertebrae (ankylosis). Accurately assessing and monitoring this structural progression is crucial for understanding the disease course, evaluating treatment efficacy, and guiding patient management. While clinical measures like the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) assess symptoms and inflammation, and the Bath Ankylosing Spondylitis Functional Index (BASFI) evaluates functional limitations, the mSASSS specifically focuses on the radiographic evidence of structural damage.

The Purpose of the mSASSS

The primary purpose of the mSASSS is to provide a quantitative and objective measure of spinal structural changes over time in patients with AS. Its key applications include:

• Monitoring Disease Progression: Tracking changes in the mSASSS score over years helps clinicians understand the rate of radiographic progression of AS in individual patients.
• Assessing Treatment Efficacy: It serves as a critical outcome measure in clinical trials, particularly for evaluating the effectiveness of disease-modifying therapies, such as biologic agents, in slowing or halting spinal damage.
• Prognostic Indicator: A higher baseline mSASSS or a rapid increase in score can indicate a more severe disease course and potentially greater functional impairment.
• Research Tool: It provides a standardized method for comparing structural damage across different patient cohorts and studies.

Components of the mSASSS

The mSASSS evaluates the spine based on plain film X-rays, specifically focusing on two key regions:

• Cervical Spine (Lateral View): This view assesses the vertebral bodies from C2 to C7.
• Lumbar Spine (Lateral View): This view assesses the vertebral bodies from T12 to L5.

The score is derived from evaluating the anterior and posterior corners of each vertebral body within these segments.

Scoring Criteria for Each Vertebral Corner:

Each vertebral corner (anterior and posterior) is assigned a score from 0 to 3 based on the observed radiographic changes:

• 0: Normal - No evidence of erosion, sclerosis, or syndesmophyte formation.
• 1: Erosion or Sclerosis - Presence of erosions, irregularity, or increased bone density (sclerosis) at the vertebral corner.
• 2: Squaring or Syndesmophyte Formation - Loss of the normal concave anterior vertebral shape (squaring) or the presence of a rudimentary syndesmophyte (new bone formation bridging vertebrae).
• 3: Bridging Syndesmophyte - Complete bridging of the vertebral body corners, indicating fusion.

Total Score Calculation:

• For the cervical spine (C2-C7), there are 6 vertebral bodies, each with 2 corners (anterior and posterior), resulting in 12 evaluable corners. With a maximum score of 3 per corner, the maximum cervical score is 36 (12 corners x 3 points).
• For the lumbar spine (T12-L5), there are 6 vertebral bodies, each with 2 corners (anterior and posterior), resulting in 12 evaluable corners. With a maximum score of 3 per corner, the maximum lumbar score is 36 (12 corners x 3 points).
• The total mSASSS score ranges from 0 to 72.

Distinction from Original Stoke AS Score:

The "Modified" aspect of the mSASSS refers to its refinement from the original Stoke Ankylosing Spondylitis Spine Score (SASSS). The key modifications include:

• Exclusion of Sacroiliac Joints: The mSASSS focuses solely on the spine, whereas the original SASSS included assessment of the sacroiliac joints.
• Exclusion of Thoracic Spine: The mSASSS omits the thoracic spine due to challenges in consistent and clear radiographic visualization, focusing on the more reliably imaged cervical and lumbar regions.

Scoring and Interpretation

A higher mSASSS score indicates more severe and extensive structural damage (erosions, squaring, syndesmophytes, and fusion) in the cervical and lumbar spine. The score is typically assessed at baseline and then at regular intervals (e.g., every 2 years) to determine the rate of progression. A change of 2 or more units over two years is generally considered a significant progression in clinical studies, though individual clinical relevance can vary.

Clinical Significance and Applications

The mSASSS is a cornerstone in the management and research of AS due to its ability to objectively quantify irreversible structural changes.

• Disease Management: While not typically used for initial diagnosis, the mSASSS is vital for long-term monitoring. It helps clinicians understand the long-term prognosis and whether current treatments are effectively slowing the progression of spinal fusion.
• Treatment Decisions: In conjunction with clinical symptoms and inflammatory markers, mSASSS data can inform decisions regarding the initiation or adjustment of therapies, particularly for advanced biologics targeting structural progression.
• Clinical Research: It is a standard primary or secondary outcome measure in almost all clinical trials investigating new treatments for AS, providing robust evidence of a drug's impact on structural integrity.

Limitations of the mSASSS

Despite its utility, the mSASSS has several limitations:

• Radiation Exposure: It relies on plain X-rays, which expose patients to ionizing radiation, limiting the frequency of assessments.
• Insensitivity to Early Changes: X-rays primarily detect established bone changes and are less sensitive to early inflammatory lesions (e.g., bone marrow edema) that can be visualized with Magnetic Resonance Imaging (MRI).
• Does Not Reflect Inflammation or Function: The mSASSS strictly measures structural damage and does not directly correlate with current disease activity (inflammation) or a patient's functional status. Other indices (BASDAI, BASFI) are needed for this.
• Inter-Reader Variability: While standardized, some degree of variability can exist between different radiologists interpreting the X-rays.
• Does Not Capture All Aspects of AS: It focuses on the axial skeleton and does not assess peripheral joint involvement or enthesitis.

Conclusion: Importance for Fitness Professionals

For fitness enthusiasts, personal trainers, and student kinesiologists, understanding the mSASSS provides critical insight into the long-term anatomical and biomechanical challenges faced by individuals with Ankylosing Spondylitis. A high mSASSS score indicates significant spinal stiffness and reduced mobility, directly impacting exercise prescription and movement capabilities. Knowledge of this score underscores the importance of:

• Tailored Exercise Programs: Designing routines that prioritize maintaining spinal mobility, strengthening core musculature, and improving posture without exacerbating pain or risking injury in an already compromised spine.
• Understanding Client Limitations: Recognizing that clients with high mSASSS scores may have irreversible limitations in spinal flexion, extension, and rotation, necessitating modifications to common exercises.
• Collaboration with Healthcare Providers: Emphasizing the need for a multidisciplinary approach, where exercise professionals work closely with rheumatologists and physical therapists to ensure safe and effective exercise interventions that align with a client's clinical status and disease progression.

The mSASSS is more than just a number; it's a quantitative representation of the physical manifestation of AS, guiding both medical treatment and informed exercise strategies to optimize quality of life for those living with the condition.