Comparative Analysis of Japanese Clinical Note Styles Between Physicians and Large Language Models Using Identical Psychiatric Cases: Quantitative Text Analysis.

Background: With the rapid adoption of large language models (LLMs) in clinical documentation, it is unclear whether LLMs can faithfully reproduce specialty-specific writing styles and clinically meaningful documentation patterns observed in expert notes, particularly in psychiatry. Objective: This study aims to systematically compare the narrative styles of human physicians and LLMs when documenting identical psychiatric cases and to evaluate the extent to which LLMs replicate specialty-specific documentation patterns. Methods: We constructed 2 standardized outpatient scenarios in Japanese (major depressive disorder and schizophrenia) and collected 134 initial notes in Japanese authored by psychiatrists and internists, alongside notes generated by 4 LLMs simulating each specialty. We conducted lexical, syntactic, semantic, and topic-level analyses using Bilingual Evaluation Understudy (BLEU), Recall-Oriented Understudy for Gisting Evaluation-Longest Common Subsequence (ROUGE-L), BERTScore, and Translation Edit Rate (TER), complemented by redundancy metrics and medical term variation analyses. Results: LLM-generated notes were significantly longer, more repetitive, and lexically less diverse than human-authored notes. TER-based clustering revealed a uniform, template-like writing style in LLMs, diverging from the flexible, context-sensitive style of physicians. Topic modeling suggested that LLM-generated notes tended to rely on more abstract and generalized expressions, with less variation in the distribution and emphasis of documented clinical information. Conclusions: LLMs can mimic surface-level stylistic features but fall short in reproducing nuanced, context-dependent, diagnostically relevant content typical of expert clinical documentation. Future clinical use will require careful prompt design or fine-tuning to ensure narrative depth, lexical diversity, and clinical relevance.