Bell's Palsy-Unclear Terminology and Definitions Impede Progress.

Importance: Bell's palsy (BP) is reported as the most common cause of facial paralysis, yet literature lacks a standardized definition of BP. Objective: To identify and categorize how the term "Bell's palsy" is defined and applied in published medical literature. Evidence Review: Randomized controlled trials, clinical trials, systematic reviews, meta-analyses, and reviews containing "Bell's palsy" were identified in MEDLINE, Embase, and CENTRAL databases from inception until April 2, 2024. Articles were indexed by their definition of BP: (1) acute (≤72-h onset) idiopathic facial paralysis with no known etiologies, (2) acute "idiopathic" facial paralysis despite providing etiologies, (3) acute non-idiopathic facial paralysis, (4) non-acute but "idiopathic" facial paralysis with or without providing etiologies, (5) synonymous with facial paralysis, and (6) no definition. Ascribed etiologies were recorded. Original articles' exclusion criteria for patients with BP were also categorized. Findings: Of 4,395 articles obtained, 924 met the criteria. Based on the aforementioned categories, incongruent definitions of BP exist in the literature: (1) 12.88%, (2) 14.72%, (3) 4.00% (4) 15.26%, (5) 8.12%, and (6) 45.02%. Ascribed etiologies and exclusion criteria for BP also varied. Conclusions and Relevance: BP is a common condition seen by providers of many specialties, and as such patient diagnosis, management, and research rely on consistency and a shared language. This systematic review found inconsistent definitions and applications of the term "Bell's palsy" in the literature.