Epidemiology and Clinical Characteristics of Nummular Headache in Observational Studies: A Systematic Review and Meta-Analysis.

Introduction: Nummular headache (NH) is a rare primary headache disorder which was first described in 2002. This meta-analysis aimed to evaluate the prevalence and relative frequencies of clinical features of NH.

Methods: PubMed, Embase, Medline, and ScienceDirect were thoroughly searched for observational studies reporting the relevant data regarding NH diagnosed in accordance with ICHD-2, ICHD-3β, ICHD-3, or Pareja's original study. Random-effects meta-analysis was performed in order to calculate the pooled prevalence estimates (PPEs) and the I2 statistics was used to measure the between-study heterogeneity. The PRISMA guidelines were strictly followed by the study's structure. The Joanna Briggs Institute Checklist for Studies Reporting Prevalence Data was used to evaluate the risk of bias of included studies.

Results: Out of initial 2,441 records, 17 studies met all of the inclusion criteria. The pooled mean age of onset of NH was 46.91 (95% confidence interval [95% CI]: 43.85-49.96). The PPE of NH in adult patients evaluated for a headache in a clinic-based setting was 0.7% (95% CI: 0.2-2.4), with slight female predominance (females = 0.5%, 95% CI: 0.2-1.4 vs. males = 0.3%, 95% CI: 0.1-0.8). The majority of patients (69.4%, 95% CI: 58.1-78.8) experience chronic course of NH. The shape of the headache was round/circular in 78.4% (95% CI: 71.9-83.7) and oval/elliptical in 21.6% (95% CI: 16.3-28.1) of patients. In 7.5% (95% CI: 2.7-19.0) of individuals, pain had multifocal location and 59.1% (95% CI: 49.7-68.0) of NH patients experienced pain exacerbations. The pain was most prevalent in the strictly parietal region (43.0%, 95% CI: 37.4-48.7) of the cranium and had pressing quality (51.4%, 95% CI: 41.6-61.1). Migraine has been diagnosed in 29.3% (95% CI: 18.5-42.9) of patients prior to NH diagnosis, and 42.4% (95% CI: 33.5-51.8) of patients experience a complete remission, with or without medication, of headache.

Conclusion: The results of our study showed that NH is a very distinct and relatively rare to encounter headache disorder. Due to its unique clinical phenotype, physicians need to be aware when a patient presents with a small, well-localized round/oval headache in the cranium region.