A Search for Undiagnosed Charcot-Marie-Tooth Disease Among Patients Registered with Unspecified Polyneuropathy in the Danish National Patient Registry

Abstract

Purpose

In a recent study based on data from the Danish National Patients Registry (DNPR), we reported the prevalence of Charcot-Marie-Tooth disease (CMT) in Denmark to be 22.5 per 100.000. This prevalence is most likely a minimum estimate, as many cases of CMT may be misdiagnosed or remain undiagnosed due to the heterogeneous nature of the disorder. The aim of this study was to investigate the possible number of undiagnosed CMT cases among patients registered with unspecified polyneuropathy (UP) diagnoses in the DNPR.

Patients and Methods

From the DNPR we extracted data on all patients given an UP diagnosis in the period 1977 to 2012. We selected all patients diagnosed with a primary UP diagnosis before age 40 at a department of neurology, neurophysiology, clinical genetics or pediatrics, and excluded all patients with a specified polyneuropathy diagnosis or with diagnostic codes related to alcohol and diabetes mellitus. To assess the proportion of possible CMT patients, we performed medical record review in a random sample of patients diagnosed in the Central Denmark Region. To further investigate the possible overlap between UP and CMT in the DNPR, we performed a series of searches for ICD-8 and ICD-10 codes related to CMT.

Results

Between 1977 and 2012, 30.903 patients were diagnosed with UP without also being diagnosed with CMT. A total of 940 patients fulfilled the selection criteria. We found that 21.5% (95% CI 13.1%–32.2%) of the cases in the random sample fulfilled our criteria for CMT. This estimate increases the prevalence of CMT in Denmark with 3.6 per 100,000 (95% CI 2.4%–5.5%).

Conclusion

This study illustrates how hitherto undiagnosed CMT patients may be identified in the DNPR and further reports the number of possible CMT cases. Our results support the hypothesis that the true prevalence of CMT is higher than recently reported.

Keywords:

• registries
• International Classification of Disease codes
• epidemiology
• hereditary neuropathy

Acknowledgments

We are grateful to the following for assistance in medical records retrieval: Anita Højholt, Department of Neurology, Aarhus University Hospital, Birgitte Forsom Sandal, Department of Neurology, Holstebro Regional Hospital West Jutland, Friedrich Emanuel Schlesinger, Department of Neurology, Viborg Regional Hospital Central Jutland, Hatice Tankisi, Department of Neurophysiology, Aarhus University Hospital, Lene Vels Pedersen, Department of Pediatrics, Herning Regional Hospital West Jutland and Thomas Helweg Thelle, Department of Pediatrics, Viborg Regional Hospital Central Jutland. We also wish to thank Michael Væth from The Department of Public Health, Section for Biostatistics at Aarhus University for technical assistance in management of register data and review of the statistical analyses. This work has been supported by a grant from Innovation Fund Denmark, Aarhus University Hospital and Aarhus University.

Author Contributions

All authors made substantial contributions to conception and design, acquisition of data, or analysis and interpretation of data; took part in drafting the article or revising it critically for important intellectual content; agreed to submit to the current journal; gave final approval of the version to be published; and agree to be accountable for all aspects of the work.

Disclosure

The authors report no conflicts of interest in this work.