Charcot foot (CF) is a serious complication of diabetes in patients with distal peripheral neuropathy. The reported incidence (0.1–29.0%) and prevalence (0.08–13.00%) of CF has varied considerably (1–3) in previous small studies. In a large recent study investigators reported a prevalence of 0.56% but did not distinguish between the types of diabetes (4). The aim of the current study was to determine the prevalence of CF in subjects with type 1 or type 2 diabetes on a nationwide scale.
This was an observational study with a study period between 1 January 2001 and 31 December 2016. Data from three Swedish registries were used: the National Patient Register, containing ICD-10 codes associated with hospitalizations and outpatient visits; the National Diabetes Register (NDR); and the Prescribed Drug Register (PDR). However, due to restriction on data availability from PDR, incidence and prevalence of CF were only studied between 2006 and 2016. All centers in Sweden where patients with diabetes and CF receive care contributed automatically with data to those registries. Diabetes was defined on the basis of an inpatient or outpatient visit for which an appropriate ICD-10 code was recorded (E10–E14) and/or records of a dispensed prescription of an antidiabetes drug. Type 1 and type 2 diabetes were defined with ICD-10 codes E10 (with data collection through use of the National Patient Register and/or the NDR, where the sole use of insulin did not classify subjects as having type 1 diabetes) and E11, respectively. Information for subjects identified in PDR was linked with that in NDR, and the appropriate ICD-10 code was retrieved. In case of discrepancy regarding the recorded diagnostic codes for the types of diabetes, the most recent record was assumed to be accurate. Classification of diabetes type was possible for 81% (2006), with improved coverage during later years, e.g., 92.5% (2016). CF was defined with a diagnosis of M14.2, M14.6, and M90.8. The date of diabetes diagnosis was considered as either the date of the initial diagnosis (from NDR) or the date of the first prescription of antidiabetes drugs—whichever came first.
Relative incidence of diabetic CF was defined as the number of new diagnosed subjects identified during a calendar year divided by the total number of subjects with respective type of diabetes alive at the start of the year. The prevalence for each year was defined as the total number of alive subjects with diabetes and CF divided by the total number of alive subjects with diabetes for respective type. Two-sample tests of proportions were conducted to test for differences in incidence and prevalence of CF between type 1 and type 2 diabetes, respectively. The time from onset of diabetes to initial diagnosis of CF was visualized with Kaplan-Meier survival curves, and the difference in time to event was tested with the log-rank test of equality.
A total of 3,449 subjects with diabetes and CF were initially identified, of whom 62.1% had type 2 diabetes. Mean ± SD duration of diabetes before the appearance of CF was 33.113.4 years for subjects with type 1 compared with 14.69.5 years for subjects with type 2 diabetes (log-rank test, P < 0.001) (Fig. 1). The mean age of the two groups was 52.812.1 and 65.010.6 years, respectively. At the end of the study period, 2,922 subjects with CF were still alive in a total population of 371,345 subjects with diabetes.
Relative incidence and prevalence of CF among subjects with type 1 diabetes and subjects with type 2 diabetes (A) and incidence of CF among subjects with type 1 diabetes or type 2 diabetes according to duration of disease (B). The Kaplan-Meier curve plotted depicts the cumulative incidence of CF diagnosis.
Relative incidence and prevalence of CF among subjects with type 1 diabetes and subjects with type 2 diabetes (A) and incidence of CF among subjects with type 1 diabetes or type 2 diabetes according to duration of disease (B). The Kaplan-Meier curve plotted depicts the cumulative incidence of CF diagnosis.
Between 2006 and 2016, the incidence varied from 228 to 287 new CF cases per year without a clear pattern (range 67–92 for subjects with type 1 and 113–180 for subjects with type 2 diabetes) with a relative incidence between 6.4 and 9.5 per 10,000 subjects with diabetes (12.1–17.6 for type 1 and 5.6–7.9 for type 2 diabetes; two-sample test, P < 0.001). The prevalence increased, from 0.55% in 2006 to 0.79% in 2016. This trend was observed for both subjects with type 1 diabetes (from 1.06 to 1.97%) and subjects with type 2 diabetes (from 0.42 to 0.60%; two-sample test, P < 0.001) (Fig. 1).
The current study, including the largest cohort of subjects with CF secondary to diabetes studied to date, has permitted us to provide new epidemiological data on CF. The relative incidence and prevalence of CF is higher among subjects with type 1 diabetes in comparisons with those with type 2 diabetes. The prevalence increased with time for both types of diabetes. Consistent with the results of previous studies, duration of diabetes before onset of CF was longer, and age of onset lower, for subjects with type 1 diabetes in comparison with those with type 2 diabetes (5). However, since our study is register based, there is a limitation regarding the distinction of the different forms of CF. Furthermore, some subjects with diet-managed diabetes and CF may not have been included in the study. Carefully planned prospective studies are needed to confirm our findings.
Article Information
Funding. Funding was received from the Swedish Research Council, Stockholm County Research Council, Berth von Kantzows Foundation, Kung Gustaf V’s och Drottning Victorias Frimurarestifelse, Karolinska Institutet Research Foundation, Strategic Research Programme in Diabetes, and Diabetesfonden.
Duality of Interest. No potential conflicts of interest relevant to this article were reported.
Authors Contributions. G.T. was involved in the conceptualization, data curation, formal analysis, investigation, methodology, software, validation, visualization and writing of the original draft of the manuscript. N.R.E. and T.F. were involved in the investigation, methodology, supervision, validation, and reviewing and editing the draft of the manuscript. S.-B.C. was involved in the conceptualization, funding acquisition, investigation, methodology, project administration, resource finding, supervision, validation, and reviewing and editing the draft. G.T. and S.-B.C. are the guarantors of this work and, as such, had full access to all the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. G.T. wrote the first draft of the manuscript, and all authors edited, reviewed, and approved the final version of the manuscript.
Prior Presentation. Parts of this study were presented in abstract form at the 58th Annual Meeting of the European Association for the Study of Diabetes, 19–23 September 2022, Stockholm, Sweden.
