Multiple Sclerosis Severity Scoring Systems: EDSS, MSSS, and ARMSS

The Expanded Disability Status Scale (EDSS), Multiple Sclerosis Severity Score (MSSS), and Age Related Multiple Sclerosis Severity Score (ARMSS) are pivotal in evaluating the severity and progression of Multiple Sclerosis (MS). Each system has its specific advantages, disadvantages, and methodologies for calculation, providing essential insights into patient management and research. Expanded Disability Status Scale (EDSS)
Advantages:
Widely Used: The EDSS is the most commonly used scale in clinical trials and research studies for MS, providing a standardized method for evaluating disability.

Comprehensive: It covers a range of functional systems (FS), including visual, brainstem, pyramidal, cerebellar, sensory, bowel and bladder, and cerebral functions.

Disadvantages:
Subjectivity: The scale's reliance on clinical examination can lead to inter-observer variability.

Mobility Focus: The EDSS is heavily weighted towards mobility, particularly in its higher scores, potentially underrepresenting cognitive, sensory, and other non-motor disabilities.

Plateaus: Patients often experience plateaus in the mid-range of the scale, where significant changes in non-mobility functions may not result in changes in the EDSS score.

Calculation:
The EDSS score is determined after assessing the FS and walking ability. Scores range from 0 (normal neurological exam) to 10 (death due to MS) in 0.5 unit increments. The key determinant in higher scores (4.0 to 7.5) is the ability to walk, with specific distances and aid requirements defining different scores.

Multiple Sclerosis Severity Score (MSSS)
Advantages:
Disease Duration Adjustment: The MSSS adjusts the EDSS score for disease duration, providing a more nuanced view of disease severity over time.

Comparative Analysis: It enables comparisons of disease severity across different populations and studies.

Disadvantages:
Reliance on EDSS: It inherits the EDSS's limitations regarding subjectivity and focus on mobility.

Data Requirements: Accurate calculation requires precise disease onset, which may not always be available or accurately remembered by patients.

Calculation:
The MSSS is calculated by comparing an individual’s disability level (EDSS) with the distribution of EDSS scores in a reference population with similar disease durations. The scores are then converted into deciles, with lower scores indicating a better prognosis and higher scores indicating a more severe disease course relative to peers.

Age Related Multiple Sclerosis Severity Score (ARMSS)

Advantages:
Age as a Metric: By using age, the ARMSS addresses the ambiguity in disease onset dates, potentially increasing its applicability and accuracy.

Comparability: Similar to the MSSS, it facilitates comparison between individuals and populations.

Disadvantages:
Less Disease Duration Sensitivity: While age is a more straightforward metric, it may not capture the nuances of disease progression as sensitively as disease duration.

Calculation:
The ARMSS ranks individuals by their EDSS scores within age groups, rather than by disease duration. This method involves comparing a patient's disability level to a reference population of the same age, offering a percentile score that reflects how an individual's disability compares to peers of the same age.

Conclusion
Each of these scoring systems plays a crucial role in the management and research of MS. The EDSS offers a detailed assessment of disability, the MSSS provides a comparative severity measure accounting for disease duration, and the ARMSS proposes an innovative age-based comparison. The choice between these systems depends on the specific goals of the assessment, whether clinical management, research, or both. Understanding the advantages, disadvantages, and calculations of each system is essential for their effective application in various contexts within the MS community.

Reference:

Pachner, A., & Steiner, I. (2009). The multiple sclerosis severity score (MSSS) predicts disease severity over time. Journal of the Neurological Sciences, 278, 66-70. https://doi.org/10.1016/j.jns.2008.11.020.
Manouchehrinia, A., Westerlind, H., Kingwell, E., Zhu, F., Carruthers, R., Ramanujam, R., Ban, M., Glaser, A., Sawcer, S., Tremlett, H., & Hillert, J. (2017). Age Related Multiple Sclerosis Severity Score: Disability ranked by age. Multiple Sclerosis (Houndmills, Basingstoke, England), 23, 1938 - 1946. https://doi.org/10.1177/1352458517690618.