Introduction

National epidemiologic surveys indicate that one in five adults in the United States can be diagnosed with a mental disorder during the course of a year⁽¹⁾. These individuals tend to have more physical health conditions concurrently with their mental disorders than those without such disorders⁽²⁾. The provision of mental health services to these individuals may be offset by the subsequent reduction in utilization and/or costs of medical care they consume, a phenomenon known as the cost-offset effect^(2,3). While the comorbidity of physical health conditions with mental disorders has been well established, the offset in costs of medical care consumed subsequent to mental health treatment in individuals needing and receiving such treatment has been less clear^(2,3). In their developmental studies of cost offset, Stiles et al. found mixed results supporting this phenomenon⁽²⁾. They suggested studying specific medical procedures, rather than the broader physical health service categories they devised and analyzed, to better detect potential offsets in costs of medical care consumed subsequent to mental health treatment⁽²⁾. Among the mixed results they found, Medicaid patients who needed and received mental health treatment incurred 18.6% lower surgical costs per user per year than patients who needed but did not receive mental health treatment⁽²⁾.

Appendectomy, the surgical removal of the appendix, is indicated in cases of acute appendicitis, which classically presents as acute lower abdominal pain, for which an inflamed appendix is suspected to be the cause⁽⁴⁾. Because of the risks of an abscess or rupture of the inflamed appendix and subsequent infection of the abdominal cavity (peritonitis), this procedure is almost always performed on an emergency basis, to avoid the risk of mortality that these complications may cause⁽⁴⁾. Approximately 341,000 nonincidental appendectomies were performed in the United States in 2006, making it the most common general surgical procedure performed on an emergency basis^(5,6). A white blood cell count may be taken to confirm inflammation and consequently a diagnosis of appendicitis if the count is elevated, thus ruling out the many other disease conditions known to cause abdominal pain^(7-9). The increased use of computed tomography (CT) as a diagnostic imaging tool to evaluate patients with abdominal pain has reduced the negative appendectomy rate, defined as the percentage of appendectomies performed without a confirmed diagnosis of appendicitis, in recent years⁽¹⁰⁾. Nevertheless, appendectomy is almost always performed, given a high index of suspicion for appendicitis, to avoid the life-threatening complications that the rupture of a potentially inflamed appendix can cause⁽⁴⁾. Crohn’s disease, a chronic idiopathic inflammatory bowel disease, is more likely to be diagnosed after an appendectomy is performed, especially within the first year⁽¹¹⁾.

Surgeons have long suspected a psychogenic cause when normal appendices are removed from patients complaining of abdominal pain⁽¹²⁾. Indeed, absence of organic disease is the second most common finding after mesenteric lymphadenitis in cases of suspected appendicitis that turned out otherwise upon surgical removal of the appendix⁽⁴⁾. Likewise, irritable bowel syndrome has also been linked to similar cases of negative appendectomy⁽⁸⁾. An analysis of Epidemiologic Catchment Area data collected by the US National Institute of Mental Health found significantly elevated lifetime rates of almost every DSM-III Axis I psychiatric disorder among those who indicated experiencing during their lifetimes two or more functional gastrointestinal symptoms commonly associated with irritable bowel syndrome, including abdominal pain⁽¹³⁾. In a series of hospital-cased clinical studies, conducted by researchers in Australia⁽¹⁴⁾, Italy⁽¹⁵⁾, New Zealand⁽¹⁶⁾, and the United Kingdom^(17-20), the relationship between mental health status and diagnosis of acute appendicitis leading to subsequent appendectomy was investigated. Through interviews of appendectomy patients and pathological examinations of resected appendices, these researchers found that severe life events, usually involving personal losses that posed a long-term threat to the patient, were associated with the onset of nonorganic, functional abdominal pain that closely mimicked acute appendicitis, thereby indicating a psychogenic origin in these particular cases of abdominal pain^(14-20). An otherwise inexplicable increase in the number of appendectomies performed over a three-and-a-half-month period in 1999 has even been documented as the result of a mass sociogenic illness among adolescent schoolgirls in an Idaho town⁽²¹⁾.

Of particular relevance to the relationship between mental health status and appendectomy is the diagnosis of nonspecific abdominal pain (NSAP). Although controversial, NSAP has been defined as a behavioral syndrome characterized by complaints of vague, recurrent, and somatic (usually abdominal) pain with no organic basis, that is associated with previous psychiatric morbidity and an ongoing need for medical attention, even after an appendectomy has been performed⁽²⁰⁾. While a variety of causes have been postulated, NSAP is most likely psychological rather than pathogenetic in origin⁽²⁰⁾. Barker and Mayou concluded that “hospital doctors and general practitioners should be trained to help patients reattribute their symptoms to a psychological cause” that would be more effective in treating these patients and would therefore lessen their utilization of medical services⁽²⁰⁾.

This study focused on a specific medical procedure with a known psychological dimension, nonincidental appendectomy, and explored its potential for a cost-offset effect, assuming that in at least certain cases, costs associated with this procedure may be reduced with appropriate mental health treatment. Using Florida hospital discharge data, the prevalence of mental disorders diagnosed during inpatient hospitalization of adult appendectomy patients was determined. Because acute appendicitis has historically been more difficult to diagnose in children, who experience a greater rate of perforation of the appendix due to their lack of classic symptoms and delay in presentation^(4,7), only adult appendectomy patients age 18 years or older were included in this study. Through bivariate and multivariate analyses, patients with and without a mental health diagnosis were compared. Finally, the implications of this study concerning the cost-offset effect and clinical practice are considered.

Methods

Data Source and Study Population

Data Analysis

Results

Bivariate Analyses

Tables 1 and 2 show the results of variables compared between patients with and without a mental health diagnosis. Out of 209,822 adult appendectomy patients, 10,774 (5.1%) had at least one mental health diagnosis, and of these, only 888 (8.2%) had two or more diagnoses. On average, these patients with a mental health diagnosis were older than patients not diagnosed with a mental disorder, with greater percentages of females and whites. Also, among those with a mental health diagnosis as compared to those without a mental health diagnosis, there were a greater percentage of those publicly insured and a lesser percentage of uninsured/underinsured/other or commercially insured. Greater percentages of those with a mental health diagnosis had a negative appendectomy, irritable bowel syndrome, or ill-defined right-lower abdominal pain. On average, those with a mental health diagnosis stayed 0.8 day longer in the hospital and incurred 30% higher total hospital charges than did those not diagnosed with a mental disorder. The greatest difference was seen in patients diagnosed with a psychotic disorder; these patients stayed on average 5.4 days longer in the hospital and incurred 109% higher total hospital charges than did patients not diagnosed with a mental disorder. No difference in diagnoses of Crohn’s disease was seen between patients with and without a mental health diagnosis.

Figure 1

Table 1: Bivariate analyses of Florida adult appendectomy patient categorical variables by diagnosed mental disorders, 1994-2009

Figure 2

Table 2: Bivariate analyses of Florida adult appendectomy patient continuous variables by diagnosed mental disorders, 1994-2009

Trend Analyses

Figure 1 shows the respective prevalence of each mental health diagnosis group among Florida adult appendectomy patients each year from 1994 through 2009. While the prevalence of most mental health diagnosis groups remained relatively constant, the prevalence of two groups increased sharply over the time period studied, specifically neurotic disorders, which increased by 768% from 0.4% in 1994 to 3.2% in 2009, and depressive disorder not elsewhere classified, which increased by 417% from 0.5% in 1994 to 2.4% in 2009.

Figure 3

Figure 1: Prevalence of diagnosed mental disorders among Florida adult appendectomy patients by year, 1994-2009

Figure 2 shows the mean total hospital charges incurred by each mental health diagnosis group each year from 1994 through 2009. After adjusting for inflation in the manner described above, a general upward trend is apparent in most groups. All groups had incurred higher mean total charges in any given year than patients not diagnosed with a mental disorder.

Figure 4

Figure 2: Mean total hospital charges (in 2009 U.S. dollars) incurred by Florida adult appendectomy patients by diagnosed mental disorders and year, 1994-2009

Multivariate Analyses

Tables 3, 4, and 5 show the results of logistic regression equations modeling mental health diagnoses as a function of Florida adult appendectomy patient variables. The models show that each age group above age 28 had significantly greater odds of being diagnosed with a mental disorder than the reference age group (age 18-28), except schizophrenic and affective disorders in the oldest quartile (age 55-103), who had significantly lower odds of being diagnosed with these mental disorders than all younger age groups. All older age groups also had significantly lower odds of being diagnosed with other mental disorders not otherwise classified than the reference age group. Female patients had significantly greater odds of being diagnosed with affective, neurotic, and depressive disorders than male patients, and significantly lower odds of being diagnosed with psychotic, schizophrenic, and other mental disorders not otherwise classified. The models also show that nonwhite from each of the different groups of Black, Hispanic, Asian or Pacific Islander, and Other or not available had significantly lower odds of being diagnosed with affective, neurotic, depressive, and other mental disorders not otherwise classified than white non-Hispanic patients. The odds for a negative appendectomy were only significantly greater among patients diagnosed with neurotic or other mental disorders not otherwise classified, and significantly lower among patients diagnosed with depressive disorders. The odds of being diagnosed with irritable bowel syndrome were significantly greater among patients diagnosed with affective, neurotic, depressive, or other mental disorders not otherwise classified. The odds of being diagnosed with ill-defined right-lower abdominal pain were significantly greater among patients diagnosed with neurotic, depressive, or other mental disorders not otherwise classified.

Figure 5

Table 3: Stratified logistic regression analyses of total mental disorders, psychotic disorders, and schizophrenic disorders as a function of Florida adult appendectomy patient variables, 1994-2009

Figure 6

Table 4: Stratified logistic regression analyses of affective and neurotic disorders as a function of Florida adult appendectomy patient variables, 1994-2009

Figure 7

Table 5: Stratified logistic regression analyses of depressive and other mental disorders as a function of Florida adult appendectomy patient variables, 1994-2009

The odds of being publicly insured were significantly greater among patients diagnosed with psychotic, schizophrenic, affective, neurotic, depressive, or other mental disorders not otherwise classified. The odds of being uninsured or underinsured were significantly lower among patients diagnosed with neurotic, depressive, or other mental disorders not otherwise classified, and significantly greater among patients diagnosed with a psychotic disorder. The odds of being commercially insured were significantly lower among patients diagnosed with psychotic, schizophrenic, affective, neurotic, depressive, or other mental disorders not otherwise classified.

Finally, the logistic models show that patients diagnosed with psychotic or schizophrenic disorders had significantly greater odds of incurring a length of stay above two days, and patients diagnosed with other mental disorders not otherwise classified had significantly greater odds of incurring a length of stay above three days. On the other hand, patients diagnosed with neurotic or depressive disorders had significantly lower odds of incurring a length of stay above three days. Patients diagnosed with affective, neurotic, depressive, or other mental disorders not otherwise classified had significantly greater odds of incurring total hospital charges at or above the second quartile ($18,941 or more), while patients diagnosed with a psychotic disorder had significantly greater odds of incurring total hospital charges at or above the third quartile ($26,860 or more). Patients diagnosed with a schizophrenic disorder had significantly greater odds of incurring total hospital charges in the top quartile ($39,106 or more).

As an exploratory analysis to determine if extra cost and length of stay was caused by the psychological/psychiatric consultation, a subset analysis was performed. The Florida hospital discharge data set breaks out behavioral health charges starting in 2006. Analysis of 5,392 appendectomy patient records with at least one mental health diagnosis in the 2006-2009 data showed that only four patients had incurred such charges averaging $294 (in 2009 dollars).

Discussion

Bivariate and multivariate analyses of Florida adult appendectomy patient variables by diagnosed mental disorders revealed significant differences between patients with and without a mental health diagnosis. In particular, variables found to be associated with psychopathology in previous studies^(8,14-20) were also found to be associated with certain mental disorders in this study. For example, negative appendectomy was positively associated with neurotic or other mental disorders not otherwise classified. Irritable bowel syndrome was associated with affective, neurotic, depressive, or other mental disorders not otherwise classified. Ill-defined right-lower abdominal pain was associated with neurotic, depressive, or other mental disorders not otherwise classified. Conversely, however, negative appendectomy was negatively associated with depressive disorder not elsewhere classified. Being publicly insured was associated with psychotic, schizophrenic, affective, neurotic, depressive, or other mental disorders not otherwise classified, consistent with national statistics on public mental health care expenditures⁽³⁰⁾. No difference in diagnoses of Crohn’s disease was found between patients with and without a mental health diagnosis; consequently, Crohn’s disease was not included as a covariate in the multivariate analyses.

Consistent with the ICD-9-CM disease classification system, patients assigned ICD-9-CM diagnosis code 311 for depressive disorder not elsewhere classified, who comprised one-third of all patients diagnosed with a mental disorder in this study, were analyzed as a separate mental health diagnosis group because they did not meet diagnostic criteria for clinical depression under ICD-9-CM diagnosis code 296 for major affective disorder. These patients had lower odds for a negative appendectomy, the only mental health diagnosis group in which this was the case. At the same time, they also had greater odds of being diagnosed with ill-defined right-lower abdominal pain. These associations suggest that this mental disorder may possibly share a common etiologic pathway with appendicitis and abdominal pain, which would have been masked had this mental health diagnosis group been merged with another. In addition, diagnosis and reporting of this mental disorder have changed over the time period studied, as evidenced by the sharp increase in its prevalence. Therefore, depressive disorder not elsewhere classified was analyzed separately from other mental health diagnosis groups in this study.

In contrast to hospital-based clinical studies, which enrolled a relatively small series of appendectomy patients and evaluated their mental health status ^(8,14-20), this study was based on a secondary analysis of appendectomy patient records abstracted from a large, population-based hospital discharge administrative data set. Most states collect hospital discharge data for the primary purpose of billing insurers to reimburse hospitals for charges incurred by patients during inpatient hospitalization⁽³¹⁾. Data are reported on the standard Uniform Bill (UB) form and capture patient demographics, procedures performed, discharge diagnoses, and other aspects of the hospitalized patient’s inpatient stay that are of interest to health services researchers⁽³¹⁾. Thus, hospital discharge data are a convenient and inexpensive source of secondary research data, given the large sample sizes available that would have been much more difficult and costly to obtain via primary data collection⁽³¹⁾. The strengths of this study therefore lay in the large sample sizes available in the hospital discharge data set that were able to confer adequate statistical power to detect differences between patients with and without a mental health diagnosis, between mental health diagnosis groups, and between variable subcategories in the bivariate and multivariate analyses. Such large sample sizes also made statistical overadjustment of the logistic models very unlikely, with the possible exception of schizophrenic disorders, which were the smallest stratum of mental disorders analyzed in this study with only 332 patients. Trending of results over time was possible given the multiple years of data available. Finally, since the hospital discharge data set was population-based, results can be generalized to the population of adults who undergo an appendectomy in the state of Florida.

However, using hospital discharge data in this study was not without its limitations. Despite the use of the standard UB reporting form, variations in data reporting between hospitals have been observed⁽³¹⁾. Because these data were collected for the primary purpose of billing insurers and not for research, some diagnosis codes may have been overreported, and other diagnosis codes underreported, to maximize reimbursement, resulting in possible selection bias⁽³¹⁾. In this study, 5.1% of Florida adult appendectomy patients were diagnosed with a mental disorder during their inpatient hospital stay. Inclusion of the 21 extra diagnosis code fields in the 2006-2009 data that were not included in this analysis would have reclassified 641 patients from having no mental health diagnosis to having at least one mental health diagnosis, increasing the prevalence of diagnosed mental disorders in this study population to only 5.4%. Given the known higher prevalence of mental disorders in the US general adult population and among gastrointestinal patients in particular, mental disorders in this study population appear to be either underdiagnosed or underreported in this data set. In addition, variables for statistical modeling were limited to those available in this data set, and no causal relationships can be inferred from the analysis results as they were simply statistical associations between variables. Furthermore, reported dollar amounts reflect charges billed by hospitals⁽³¹⁾, which are usually higher than actual reimbursements paid by insurers. Finally, no patient follow-up was possible in this study, nor were linkages possible to records of care provided in outpatient settings. Nevertheless, despite these limitations, the statistical associations found in this secondary analysis of hospital discharge administrative data were remarkable for their consistency with hospital-based clinical studies that indicated an association between psychopathology and functional abdominal pain^(8,14-20).

This study found that adult appendectomy patients diagnosed with certain mental disorders had greater odds of incurring longer hospital stays and higher total hospital charges than patients not diagnosed with a mental disorder. Psychotic and schizophrenic disorders were associated with lengths of stay above two days, and other mental disorders not otherwise classified above three days. Affective, neurotic, depressive, and other mental disorders not otherwise classified were associated with hospital charges totaling $18,941 or more, psychotic disorders totaling $26,860 or more, and schizophrenic disorders totaling $39,106 or more. Trend analysis revealed that such patients incurred anywhere from 0.7% to 153% higher mean total hospital charges in any given year than patients not diagnosed with a mental disorder. Furthermore, analysis of 5,392 appendectomy patient records with at least one mental health diagnosis in the 2006-2009 data, which broke out behavioral health charges separately, showed that only four patients had incurred such charges averaging $294 (in 2009 dollars). Clearly these patients were typically not receiving inpatient psychological/psychiatric consultation leading to extra cost and length of stay. Thus, these higher charges are assumed to be due to increased morbidity in these patients and not the use of behavioral health services. Assuming that mental health treatment would be effective in at least partially offsetting these higher charges, these charge differentials suggest that room exists for a potential reduction in total charges, and consequently the actual costs reimbursed by insurers to hospitals, to more closely match those of patients not diagnosed with a mental disorder. The type, level, and duration of mental health treatment that would be effective to achieve this offset, or even to eliminate medically unnecessary appendectomies altogether, remain to be seen. Given the known psychological dimension of abdominal pain and especially functional abdominal pain, the likely underdiagnosis of mental disorders among adult appendectomy patients, and the higher costs of treating such patients diagnosed with a mental disorder, it would seem likely that a real psychiatric offset effect can be found for patients exhibiting psychiatric morbidity who undergo or seek to undergo this particular surgical procedure. The results of such a study, if well planned and appropriately controlled for confounding to overcome the limitations of previous offset studies⁽³⁾, could provide more conclusive evidence that mental health treatment is indeed effective in offsetting the treatment costs of at least one surgical procedure, as the findings of Stiles et al. have suggested⁽²⁾. Such results would strengthen the evidence base for the psychiatric offset effect, supporting the provision of mental health services despite the prevailing trend to curtail them as a strategy for containing health care costs.

Conclusions

With a 1994-2009 prevalence of 5.1%, mental disorders among Florida adult appendectomy patients appear to be underdiagnosed and/or underreported in the state’s hospital discharge data, compared to the known higher prevalence of such disorders in the US general adult population and among gastrointestinal patients in particular. Differences in age, gender, race/ethnicity, length of stay, total hospital charges, and principal payer were found between patients with and without a diagnosed mental disorder and between mental health diagnosis groups. Negative appendectomy, irritable bowel syndrome, and ill-defined right-lower abdominal pain were found to be associated with certain mental health diagnosis groups, consistent with findings of an association between psychopathology and functional abdominal pain in hospital-based clinical studies^(8,14-20). Being publicly insured was also found to be associated with certain mental health diagnosis groups, as well as longer hospital stays and higher charges, suggesting a potential psychiatric offset effect in which some sort of mental health treatment could offset these longer stays and/or higher charges. This study supports the need for improved diagnosis of, and referrals to appropriate mental and/or physical health treatment professionals for, mental disorders and irritable bowel syndrome in patients presenting with functional abdominal pain that is suspected to be psychogenic in origin.