# Multi-Ontology Integration with Dual-Axis Propagation for Medical Concept Representation

## TL;DR

This paper introduces LINKO, a novel framework that integrates multiple medical ontologies using dual-axis knowledge propagation and LLM-augmented initialization to improve medical concept representations in EHRs.

## Contribution

The paper presents a unified approach for cross-ontology medical concept learning by combining LLM-based initialization with dual-axis knowledge propagation, addressing limitations of prior single-ontology methods.

## Key findings

- LINKO outperforms state-of-the-art baselines in experiments.
- Enhanced robustness in limited data and rare disease scenarios.
- Effective integration of multiple ontologies improves concept representations.

## Abstract

Medical ontology graphs map external knowledge to medical codes in electronic health records via structured relationships. By leveraging domain-approved connections (e.g., parent-child), predictive models can generate richer medical concept representations by incorporating contextual information from related concepts. However, existing literature primarily focuses on incorporating domain knowledge from a single ontology system, or from multiple ontology systems (e.g., diseases, drugs, and procedures) in isolation, without integrating them into a unified learning structure. Consequently, concept representation learning often remains limited to intra-ontology relationships, overlooking cross-ontology connections. In this paper, we propose LINKO, a large language model (LLM)-augmented integrative ontology learning framework that leverages multiple ontology graphs simultaneously by enabling dual-axis knowledge propagation both within and across heterogeneous ontology systems to enhance medical concept representation learning. Specifically, LINKO first employs LLMs to provide a graph-retrieval-augmented initialization for ontology concept embedding, through an engineered prompt that includes concept descriptions, and is further augmented with ontology context. Second, our method jointly learns the medical concepts in diverse ontology graphs by performing knowledge propagation in two axes: (1) intra-ontology vertical propagation across hierarchical ontology levels and (2) inter-ontology horizontal propagation within every level in parallel. Last, through extensive experiments on two public datasets, we validate the superior performance of LINKO over state-of-the-art baselines. As a plug-in encoder compatible with existing EHR predictive models, LINKO further demonstrates enhanced robustness in scenarios involving limited data availability and rare disease prediction.