Nature and Extent of Physical Comorbidities Among Korean Patients With Mental Illnesses: Pairwise and Network Analysis Based on Health Insurance Claims Data

Objective The nature of physical comorbidities in patients with mental illness may differ according to diagnosis and personal charac-teristics. We investigated this complexity by conventional logistic regression and network analysis. Methods A health insurance claims data in Korea was analyzed. For every combination of psychiatric and physical diagnoses, odds ra-tios were calculated adjusting age and sex. From the patient-diagnosis data, a network of diagnoses was constructed using Jaccard coeffi-cient as the index of comorbidity. Results In 1,017,024 individuals, 77,447 (7.6%) were diagnosed with mental illnesses. The number of physical diagnoses among them was 11.2, which was 1.6 times higher than non-psychiatric groups. The most noticeable associations were 1) neurotic illnesses with gas-trointestinal/pain disorders and 2) dementia with fracture, Parkinson's disease, and cerebrovascular accidents. Unexpectedly, the diagno-sis of metabolic syndrome was only scarcely found in patients with severe mental illnesses (SMIs). However, implicit associations be-tween metabolic syndrome and SMIs were suggested in comorbidity networks. Conclusion Physical comorbidities in patients with mental illnesses were more extensive than those with other disease categories. However, the result raised questions as to whether the medical resources were being diverted to less serious conditions than more urgent conditions in patients with SMIs.