Background/Purpose: Psoriatic arthritis (PsA) is an autoimmune musculoskeletal disease with protean manifestations, and therefore can be difficult to diagnose. Although no diagnostic criteria are available, the CASPAR classification criteria (CC) have a sensitivity and specificity of 91.4% and 98.7%, respectively. The purpose of this study is to assess the validity of using ICD-9 codes to identify PsA patients for future clinical trials by applying the CC to patients with the ICD-9 code for PsA (696.0).

Methods:

This was a retrospective cohort study. All patients with a billing code of 696.0 seen at a single center from January 1, 2013 through December 31, 2014 were identified. Medical records were reviewed to identify all elements of CC including: Evidence of psoriasis – current psoriasis, personal history of psoriasis, family history of psoriasis; Psoriatic nail dystrophy – onycholysis, pitting, hyperkeratosis; Negative test for rheumatoid factor; Dactylitis – current dactylitis, history of dactylitis; Radiologic evidenceof juxta-articular new bone formation. The percentage of patients who met CC was calculated, and their clinical characteristics described.

Results:

1405 patients were coded as PsA. Of 1278 unique charts available for review, 629 met CC. 96 were excluded due to a concurrent clinical diagnosis of rheumatoid arthritis, inflammatory bowel disease, or gout, leaving 533 (41.7%) with PsA based on CC. Similar age and sex between ICD-9 vs. CC groups; 54.2 years vs 52.8 years; 55.2% vs 52.2% female, respectively. Compared to published data for the classification criteria,¹ in our cohort of 533 patients who met criteria, there was a similar prevalence of psoriasis (98.9% vs 98.3%), a lower prevalence of nail disease (27.0% vs 60.0%) and moderately similar prevalence of dactylitis (31.3% vs 57.5%). Other radiographic evidence of juxta-articular new bone formation was much less frequently reported. (1.7% vs 54.0%).

Conclusion:

In this study of patients with ICD-9 codes for PsA, only 41.7% met CASPAR classification criteria. This underscores differences between PsA patients meeting CC recruited for clinical trials, and those treated in an academic real world setting. These differences are important to understand when assessing generalizability of trial data, and for planning studies of clinical effectiveness in PsA.

Table 1. 1278 Charts Reviewed

Table 2. 533 patients who met CASPAR criteria (CASPAR score ≥3)

 1. Taylor et al. Arthritis & Rheumatism. Volume 54, Issue 8, pages 2665-2673, August 2006.

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