Background/Purpose: Systemic sclerosis (SSc) is a rare autoimmune disease associated with substantial morbidity.  Epidemiologic studies using large administrative databases often rely on the accuracy of International Classification of Diseases-Clinical Modification-9 (ICD-CM-9) codes for case definitions of medical conditions such as SSc. A previous study of 89 hospitalized patients at a tertiary care center found that the accuracy of ICD-CM-9 code 710.1 for determining true cases of SSc that met the 1980 ACR criteria was 45%.  We sought to determine the accuracy of the ICD-CM-9 code of 710.1 for identifying cases of SSc using a large outpatient cohort of well-characterized patients.

Methods: This was a retrospective analysis of the medical records of all patients evaluated at Stanford Hospital and Clinics from 2005-2012 who have an associated ICD-CM-9 code of 710.1.  True cases of SSc were defined as any of the following: a) Fulfill the 1980 American College of Rheumatology (ACR) classification criteria for SSc; b) Have at least 3 of 5 of the CREST (calcinosis, Raynaud’s, esophageal dysmotility, sclerodactyly, telangiectasias) features; OR c) Fulfill preliminary ACR/European League Against Rheumatism (EULAR) revised criteria for the classification of SSc.

Results: 432 patient records were reviewed.  Mean age was 57±14.5 years, 84% were female, 51% Caucasian.  21% had diffuse cutaneous disease, 66% had limited disease, and 3% were characterized as SSc sine sclerosis.  238 (55%) patients met the 1980 ACR criteria, 292 (68%) patients met CREST criteria, and 297 (69%) patients met the revised ACR/EULAR criteria. The accuracy of ICD-9-CM code 710.1 for determining true cases of SSc by any of the three classification criteria was 77%.  The ICD-CM-9 code for SSc was accurate 71% of the time when the 1980 ACR criteria were applied, and 75% of the time when the CREST or ACR/EULAR revised criteria were applied.

Table 1: Clinical Characteristics of 432 Systemic Sclerosis Patients by Criteria

Classification Criteria	Percentage of patients affected
1980 ACR Criteria:
Major criterion:
Proximal diffuse (truncal) sclerosis (skin tightness, thickening, non-pitting induration)	42%
Minor criteria:
Sclerodactyly (only fingers and/or toes)	63%
Digital pitting scars or loss of substance of the digital finger pads (pulp loss)	25%
Bilateral basilar pulmonary fibrosis	29%
Patients who met the major criterion or 2 minor criteria:	55%
CREST Criteria
Calcinosis	12%
Raynaud’s Phenomenon	82%
Esophageal dysmotility	60%
Sclerodactyly	63%
Telangiectasias	49%
Patients who met 3 of 5 CREST criteria:	68%
Revised ACR/EULAR Criteria
Skin thickening of the fingers
puffy fingers	25%
whole finger distal to MCP	47%
Fingertip lesions
digital ulcers	28%
pitting scars	21%
Abnormal nailfold capillaries	33%
Pulmonary involvement
Pulmonary hypertension	20%
Interstitial lung disease	29%
Autoantibody profile
Positive ANA	62%
Positive scl-70 Ab	11%
Positive anti-centromere Ab	20%
Patients who scored ≥ 9 points in the revised ACR/EULAR criteria:	69%
*Raynaud’s, telangiectasia percentages already noted above.

Conclusion:

We found an acceptable accuracy rate of 77% for the ICD-CM-9 code 710.1 for determining true cases of SSc according to any of 3 different classification schemes. Our study supports the validity of this ICD-CM-9 code for identifying cases of SSc for epidemiologic studies using administrative databases.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/validation-of-the-icd-cm-9-code-for-systemic-sclerosis-using-updated-acreular-classification-criteria/