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ICD-9 CM code 333.1 as an identifier of patients with essential tremor: a study of the positive predictive value of

Elan D Louis1, Lakeisha M Applegate, Eileen Rios

  • 1Gertrude H. Sergievsky Center, College of Physicians and Surgeons, Columbia University, New York, USA. EDL2@columbia.edu

Neuroepidemiology
|June 21, 2007
PubMed

Insights

The International Classification of Diseases code 333.1 has a low positive predictive value (49%) for identifying essential tremor (ET) cases. A unique diagnostic code for ET is needed.

Area of Science:

  • Neurology
  • Health Outcomes Research
  • Medical Informatics

Background:

  • Administrative databases are crucial for health outcomes research.
  • International Classification of Diseases (ICD-9 CM) codes are used to identify patient cohorts.
  • The diagnostic accuracy of ICD-9 CM code 333.1 for essential tremor (ET) has not been previously validated.

Purpose of the Study:

  • To determine the positive predictive value (PPV) of the ICD-9 CM code 333.1 for essential tremor.
  • To assess the impact of using exclusionary codes for parkinsonism and dystonia on the PPV of code 333.1.
  • To identify common misdiagnoses associated with code 333.1.

Main Methods:

  • Retrospective review of medical records for patients with ICD-9 CM code 333.1 at the Neurological Institute of New York.
  • Application of Consensus Criteria for Essential Tremor to validate diagnoses.
  • Analysis of diagnostic codes and patient demographics, including neurologist specialty.

Main Results:

  • The PPV of ICD-9 CM code 333.1 for essential tremor was 49.0% (472/964).
  • Exclusionary codes for parkinsonism and dystonia marginally improved PPV to 57.8%.
  • False positives included Parkinson's disease, dystonia, and various tremor types. Patients seen by general neurologists were less likely to meet ET criteria (34.6%) compared to movement disorder specialists (51.9%).

Conclusions:

  • The ICD-9 CM code 333.1 demonstrates poor performance in accurately identifying patients with essential tremor.
  • The high prevalence of ET warrants the development of a distinct and more specific diagnostic code.
  • Improving diagnostic coding accuracy is essential for reliable health outcomes research in neurology.
Abstract

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