Physical Illnesses Before Diagnosed as Schizophrenia: A Nationwide Case-Control Study

Some physical illnesses are potentially associated with the development of schizophrenia. However, few studies have investigated these associations. Here, we examined physical illnesses and medical utilization patterns existing before patients received a diagnosis of schizophrenia. We enrolled a large representative cohort of the general population in Taiwan (N = 1 000 000) and identified 1969 young patients with a new diagnosis of schizophrenia from January 1, 2000 to December 31, 2013. We conducted a nested case-control study based on risk-set sampling. Each case was age-matched and sex-matched with 4 controls selected from the general population. The case and control groups were compared on the basis of various clinical characteristics. Conditional logistic regression was used to estimate the magnitude of risk associated with newly diagnosed schizophrenia. Within the 1 year before the schizophrenia diagnosis, the cases were most likely to visit the psychiatry department, followed by internal medicine and family medicine departments. According to multivariate analysis, compared with the controls, the cases had substantially higher risk of physical conditions in the prodromal phase, including hypertension (adjusted risk ratio [aRR] = 1.93, P = .001), other forms of heart disease (aRR = 2.07, P < .001), cerebrovascular diseases (aRR = 2.96, P = .001), chronic obstructive pulmonary disease (aRR = 1.50, P = .005), asthma (aRR = 1.76, P = .003), and irritable bowel syndrome (aRR = 2.00, P < .001). A wide range of psychiatric diseases and concomitant use of medications were significantly associated with schizophrenia development. In conclusion, several physical illnesses were identified to be associated with schizophrenia development, indicating that people with these illnesses could be vulnerable to schizophrenia.