BACKGROUND The proper identification of chronic migraine is one of the mainstays for general practitioners. This study therefore aims to assess the epidemiology and determinants of chronic migraine in primary care in Italy by testing five operational case definition algorithms. METHODS Five case definition algorithms defining chronic migraine were developed to estimate the prevalence and incidence rate of chronic migraine in the Health Search database. For each algorithm, we conducted a nested case-control analysis to quantify the level of association between certain determinants and incident cases of chronic migraine. RESULTS Considering a cohort of 1,091,032 patients (52% were females), the prevalence rate of chronic migraine increased from the first to the fifth case definition algorithm ranging from 0.03 to 0.28%. No 95% confidence interval overlapped the others, and every confidence interval reliably maintained 2% precision. Incidence rates showed a growing trend (0.008-0.056 per 100,000 person-years) as well. All case definition algorithms were able to capture sex (i.e. female) and nonsteroidal anti-inflammatory drug (NSAID) overuse as statistically significant determinants of incident cases of chronic migraine. Depression was associated with a statistically significant increase of incidence rate of chronic migraine only for two case definition algorithms. CONCLUSION Our findings show that prevalence and incidence rate of chronic migraine are underestimated when compared with current literature. On the other hand, we found acceptable correctness of chronic migraine definition in the light of the association with well-known determinants.

中文翻译：

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慢性偏头痛的流行病学和决定因素：意大利初级保健中的一项真实世界队列研究，采用嵌套病例对照分析。

背景 正确识别慢性偏头痛是全科医生的主要工作之一。因此，本研究旨在通过测试五种可操作的病例定义算法来评估意大利初级保健中慢性偏头痛的流行病学和决定因素。方法 开发了五种定义慢性偏头痛的病例定义算法，以估计 Health Search 数据库中慢性偏头痛的患病率和发病率。对于每种算法，我们进行了嵌套病例对照分析，以量化某些决定因素与慢性偏头痛病例之间的关联水平。结果 考虑到 1,091,032 名患者（52% 为女性）的队列，慢性偏头痛的患病率从第一个病例定义算法增加到第五个病例定义算法，范围从 0.03% 增加到 0.28%。没有 95% 的置信区间与其他置信区间重叠，并且每个置信区间都可靠地保持了 2% 的精度。发病率也呈上升趋势（每 100,000 人年 0.008-0.056）。所有病例定义算法都能够将性别（即女性）和非甾体抗炎药 (NSAID) 的过度使用作为慢性偏头痛病例的统计显着决定因素。仅对于两种病例定义算法，抑郁症与慢性偏头痛发病率的统计学显着增加相关。结论 我们的研究结果表明，与现有文献相比，慢性偏头痛的患病率和发病率被低估了。另一方面，鉴于与众所周知的决定因素的关联，我们发现慢性偏头痛定义的正确性是可以接受的。