Schizophrenia Patients Show High Rates of Comorbid Illness

Hospital discharge records of people with a primary diagnosis of schizophrenia showed higher proportions of all comorbid psychiatric conditions and of several general medical conditions than did those of people who did not have schizophrenia.

The general medical conditions included acquired hypothyroidism, obesity, epilepsy, viral hepatitis, type 2 diabetes, essential hypertension, various chronic obstructive pulmonary diseases, and contact dermatitis and other forms of eczema, according to data from the National Hospital Discharge Survey reported in the August Psychiatric Services by researchers in the Department of Epidemiology at Walter Reed Army Institute of Research.

The survey data confirm what has been reported before: that patients with schizophrenia have higher rates of morbidity associated with some general medical conditions.

However, the study authors pointed out that virtually all existing studies of comorbid disorders in schizophrenia test hypotheses and have focused on a single comorbid condition in relatively small and nonrepresentative samples. The current study appears to be the first systematic analysis of comorbidity in general with schizophrenia in the U.S. hospitalized population.

“Our study is hypothesis-generating rather than hypothesis-testing, with the main purpose of presenting a systematic review of comorbid conditions,” said coauthor Natalya Weber, M.D., M.P.H.“ Psychiatrists can see in this very large and representative sample what conditions are more frequently comorbid with a primary diagnosis of schizophrenia compared to any other primary diagnosis among the U.S. hospital discharges.”

Weber is health science administrator in the Division of Preventive Medicine at Walter Reed Army Institute of Research.

In the study, 1979 to 2003 data from the National Hospital Discharge Survey, a nationally representative sample, were analyzed.

Out of 5,733,781 discharges during that period, researchers compared records of comorbid conditions among those with a primary diagnosis of schizophrenia (n=26,279) and those with other primary diagnoses (n=1,936,876). Proportional morbidity ratios were calculated.

The researchers found that psychiatric and behavior-related diagnoses accounted for 45 percent of comorbid diagnostic categories among schizophrenia discharges, compared with 15 percent among other discharges.

Further, the proportion of discharges with comorbid psychiatric disorders was much higher among patients discharged with a primary diagnosis of schizophrenia. These conditions included (in descending order of morbidity ratios): mild mental retardation, personality disorders, affective psychoses, nondependent abuse of drugs, adjustment reaction, alcohol dependence, drug dependence, depressive disorder not elsewhere classified, and neurotic disorders.

In addition, discharge records of patients with schizophrenia as the primary diagnosis were significantly more likely to list the following nonpsychiatric comorbid conditions (in descending order of morbidity ratios): acquired hypothyroidism, obesity and other hyperalimentation disorders, asthma, chronic airway obstruction not elsewhere classified, essential hypertension, and type 2 diabetes.

The frequency of cardiovascular and metabolic conditions comes as no surprise and has been reported widely. Psychiatrist John Newcomer, M.D., who has specialized in the research and treatment of metabolic conditions in schizophrenia and who reviewed the report for Psychiatric News, said the data likely underestimate the true prevalence of these comorbid conditions—a point the study researchers acknowledged.

“The very nature of the problem with this diagnosis [of schizophrenia] is that the patients tend to receive a lower standard of medical care, so there is going to be massive underestimation,” Newcomer told Psychiatric News. “If someone has a comorbid diagnosis, that means that someone had to see you and diagnose you and engage you in treatment. We are worried that this is a significant underestimation of the true prevalence [of medical comorbidity].”

Weber acknowledged in an interview that she and her colleagues had expected to see much higher rates of metabolic and cardiovascular disease. “We can only speculate that the conditions are underdiagnosed in patients with schizophrenia.”

One finding that was somewhat surprising was the frequency of comorbid epilepsy. “It is of interest that epilepsy was twice as prevalent among discharges with schizophrenia,” the authors wrote. “This association has no clear pathogenic mechanism and has been reported in only a few previous studies.”

Also noteworthy was the frequency of contact dermatitis and other forms of eczema. Weber told Psychiatric News that these are typically caused by contact with detergents, oils, solvents, drugs, plants, solar radiation, and other environmental agents.

“We can speculate that these skin diseases could be disproportionally present in patients with schizophrenia due to their higher exposure to these harmful environmental agents as a result of substandard living and working conditions, lower-paid manual jobs, and homelessness,” she said.“ Although these conditions were found a few times higher among discharges with a primary diagnosis of schizophrenia, they are quite rare—less than 1 percent of all comorbid conditions.”

She concluded, “The main message for clinicians is that individuals with schizophrenia have more than their share of associated, and often serious, medical conditions and thus require especially careful medical attention. This may help to timely diagnose and treat comorbid conditions and perhaps take some preventive measurements in those who are predisposed to them.”

“Psychiatric and General Medical Conditions Comorbid With Schizophrenia in the National Hospital Discharge Survey” is posted at<http://psychservices.psychiatryonline.org/cgi/content/abstract/60/8/1059>.▪