The Clinical Activity Score is a long-established measure of thyroid eye disease (TED) activity, but observers' scores are known to vary widely, potentially leading to over- or underestimating the need for additional treatment.
Study design
This UK-based prospective, cross-sectional, observational study evaluated the inter-observer variability of the CAS in 9 patients with thyroid eye disease (TED). Six clinicians assessed the CAS in all patients on the same day, and agreement between the clinicians was analyzed. The CAS is obtained by documenting the presence or absence of certain symptoms (e.g., spontaneous pain) and signs (e.g., lid swelling, conjunctival redness, chemosis) of TED; a score of ≥3 indicates active disease and provides a threshold for determining whether to offer treatment.
Outcomes
The lead ophthalmologist’s score was used as a standard. When the lead ophthalmologist’s CAS was ≥3, 35.6% of the assessors agreed with offering treatment. In 15.6% of instances, the assessor CAS was ≥3 when the lead ophthalmologist’s score was <3, indicating that treatment was recommended when it was not needed; in 20% of instances, the CAS was <3 when the lead ophthalmologist score was ≥3; and in 28.9% of instances, the CAS was <3 when the lead ophthalmologist’s score was <3. Thus, the other assessors agreed with the lead ophthalmologist 64.5% of the time and disagreed 35.6% of the time.
Limitations
This was a small sample size of only 9 patients. The evaluators were a mix of clinicians (ophthalmologists, endocrinologists, and trainees), not just ophthalmologists.
Clinical significance
Clinical decisions for patients with TED are often made based on the CAS. In addition, the CAS is a commonly used score in clinical trials and research studies. This study demonstrates that the CAS may be somewhat unreliable, with significant interobserver variability. Therefore, the CAS may need to be used with caution, or additional training in the determining of CAS should be performed. Alternatively, a different scoring system could be developed for use in determining disease activity in TED.
Financial Disclosures: Dr. Richard Allen discloses no financial relationships.