Hyperthyroidism and Erectile Dysfunction

A Population-Based Case-Control Study

J Keller; Y-K Chen; H-C Lin

Disclosures

Int J Impot Res. 2012;24(6):242-246. 

In This Article

Methods

Database

This study used administrative claims data sourced from the Longitudinal Health Insurance Database 2000 (LHID2000) for the analysis. The LHID2000 was created by the Taiwan National Health Research Institute and includes all the claims data and registration files of 1 000 000 individuals randomly sampled from the 2000 Registry for Beneficiaries of the Taiwan National Health Insurance (NHI) program. The representativeness of the LHID2000 relative to the whole population of NHI enrollees in terms of gender has been validated by the Taiwan National Health Research Institute. The LHID2000 allows researchers to trace all the medical services of these selected 1 000 000 individuals since the initiation of the Taiwan NHI program in 1995.

This study was exempted from full review by an Institutional Review Board after consulting with the director of the Taipei Medical University Institutional Review Board as the LHID2000 consists of de-identified secondary data released to the public for research purposes.

Selection of Cases and Controls

We first selected all the patients who had received their first-time diagnosis of ED (impotence, organic (ICD-9-CM code 607.84)) during ambulatory care visits between January 2001 and December 2009 (n=6545). In Taiwan, ED diagnoses are based on the results of a self-administered International Index of Erectile Dysfunction (IIEF-5) questionnaire. However, to increase ED diagnostic validity from the administrative claims data set, this study only included ED patients who had received ≥2 ED diagnoses during the period between 2001 and 2009, with at least one of the diagnoses being made by an urologist. Discussing sexuality is relatively a cultural taboo among the Taiwanese population, with most Taiwanese men being reluctant to admit suffering from a shameful condition. In addition, there is also no incentive to be diagnosed as pharmaceutical treatment for ED is not covered under the NHI program. Consequently, we believe that these ED diagnoses had high validity in Taiwan.

We then excluded patients under 18 (n=25) or over 80 (n=119) years of age because of the small case number in these two age groups. As a result, this study consisted of 6310 cases, with the date of their first ED diagnosis being assigned as the index date.

We likewise selected the controls from the LHID2000. We first limited our control group to only include subjects between 18 and 80 years of age. We also excluded all the subjects who had been diagnosed with ED since the initiation of the Taiwan NHI program in 1995. We then randomly selected 18 930 controls (3 controls per case) matched with cases in terms of age in intervals of 10 years (<30, 30–39, 40–49, 50–59, 60–69 and ≥70), urbanization level and index year. All 359 cities/towns in Taiwan were stratified into five groups ranked by urbanization level in accordance with a prior study, with 1 referring to the 'most urbanized' and 5 referring to 'least urbanized'.[13] These ranking were demarcated by a combined score of several measures, including the population density (people per km2), the proportion of people with college education levels or above (percentage), the proportion of elderly people over 65 years of age population (percentage), the proportion of agricultural workers (percentage) and the number of physicians per 100 000 population. Therefore, matching the variable of urbanization level between cases and controls helped to assure that cases and controls were reasonably similar in terms of unmeasured neighborhood socioeconomic characteristics. For controls, we considered the date of their first use of medical services occurring during the index year as the index date.

Exposure Assessment

In this study, we identified hyperthyroidism cases based on ICD-9-CM code 242 (thyrotoxicosis with or without goiter). To increase the validity of hyperthyroidism diagnoses, we only included those patients who had at least two consensus-diagnosed episodes of hyperthyroidism before the index date and who still had a hyperthyroidism diagnosis after receiving a blood test for the level of thyroid-stimulating hormone and thyroxine. In Taiwan, hyperthyroidism is generally diagnosed when thyroid-stimulating hormone levels are suppressed (<0.05) and thyroxine levels are elevated (>2.3). In addition, all the included cases had been prescribed antithyroid drugs.

Statistical Analysis

We used the SAS system (SAS System for Windows, Version 8.2, SAS Institute, Cary, NC, USA) to analyze data. χ 2 Tests were conducted to compare the differences in monthly income (NT$0–15 840, NT$15 841–25 000, ≥NT$25 001) and geographic location (Northern, Central, Eastern and Southern Taiwan), as well as medical co-morbidities. We selected medical co-morbidities including hypertension, diabetes, coronary heart disease, hyperlipidemia, obesity and alcohol abuse/alcohol dependence syndrome, which are all well-documented risk factors for ED. Conditional logistic regressions (conditioned on age group, urbanization level and index year) were conducted to explore the association between ED and having been previously diagnosed with hyperthyroidism. We further computed the odds ratio (OR) for having been previously diagnosed with hyperthyroidism stratified by age group. The conventional P≤0.05 was used to assess statistical significance.

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