Postoperative Quality of Life in Vestibular Schwannoma Patients Measured by the SF36 Health Questionnaire

INTRODUCTION

Recently there has been an increasing interest in the subjective self-assessment by patients of their own health outcomes after surgical treatment for vestibular schwannoma.^1-6 This trend has resulted from the feeling that the traditional technical measures of outcome after vestibular schwannoma surgery, such as facial nerve function and audiovestibular symptoms, are too narrow to document the many ways in which patients' lives can be affected by such treatment. Some studies have tried to address this concern by incorporating self-assessment of social, economic, and occupational activities, but are still relatively focused and condition-specific in their description of postoperative health status.^{2, 3, 5}

The short form 36 (SF36) is one of a series of patient-oriented self-assessment questionnaires that has been developed as a general outcome measurement tool for health status after medical and surgical treatments.^{7, 8} In contrast to patient-oriented but condition-specific measures, this general measurement tool attempts to assess aspects of health that are important to all patients, and not just those with vestibular schwannoma. Furthermore, the questionnaire has been applied to a large number of healthy people so as to produce a reference series of population norms⁹ that can be used to show how treated outcomes deviate from defined healthy standards. The SF36 has been well characterized and found to have a high degree of patient acceptability while maintaining internal validity and consistency on repeated testing.⁷ It is easily applied in the busy setting of a tertiary referral clinic.

The aim of this study is to examine the treatment outcomes after vestibular schwannoma surgery using the SF36 Health Survey Questionnaire. The results are standardized against age- and sex-matched controls from the general population and also examined for differences in health status outcome after treatment with respect to a variety of patient and tumor factors. The results are then discussed in the context of the more traditional technical measures of surgical outcome and the way they may influence clinical decision making for individual patients.

MATERIALS AND METHODS

Ninety consecutive patients with vestibular schwannoma who had undergone surgery using the translabyrinthine or retrosigmoid approach at Addenbrooke's Hospital with follow-up periods of greater than 18 months were asked to fill in the SF36 Health Survey Questionnaire sent to them by post. The questionnaire involves choosing one of several listed items in response to 36 questions. Each response was then processed by the method described by Ware et al.¹⁰ so as to produce raw scores for each patient in each of the eight defined health status scales: physical functioning, social function, role limitations due to physical problems, role limitations due to emotional problems, energy and vitality, mental health, pain, and general perception of health. The raw scores for each patient were then standardized against age- and sex-matched controls from the general population,⁹ averaged across various patient groups and presented in a standard way⁸ allowing comparison of postoperative health status with the appropriate healthy standard.

In the second part of the study patients were grouped according to a variety of preoperative patient factors (sex and age) and tumor factors (size and operative approach used). Each subgroup was then compared against its pair to determine if that particular preoperative factor was a significant predictor of postoperative health status.

RESULTS

Seventy-two of the 90 SF36 questionnaires were returned correctly filled in (response rate: 80%). The age- and sex-matched mean scores and standard deviation for each of the eight health domains were calculated and are presented in Figure 1. For seven of the eight measured health scales the postoperative quality of life was less than the appropriate matched healthy standard, represented by bars above and below the zero line. The energy and vitality scale was the only scale scoring slightly higher than the matched healthy standard. These findings are similar to that of Nikolopoulos et al.,⁶ who found that the majority (82.6%) of the patients surveyed using the Glasgow Benefit Inventory, a patient-oriented but relatively condition-specific health status tool designed to measure changes in otolaryngologic conditions following intervention,¹¹ reported quality of life the same or worse after vestibular schwannoma surgery.

In the second part of the results the postoperative SF36 scores for different subgroups of vestibular schwannoma patients were compared to see if there were any patient or tumor factors that could predict a poorer outcome after surgery. The appropriate nonparametric statistical test was applied to each of the preoperative factors and the P values are presented in Figure 2. A comparison of different operative approaches (translabyrinthine and retrosigmoid), tumor size (group cut of points of tumor diameter 1.5 mm and 2.5 mm), patient sex, and ranking of patient age showed no statistically significant difference in measured quality of life outcomes. These findings are shared by Nikolopoulos et al.,⁶ who also found that tumor volume did not significantly affect the postoperative quality of life, but contrasted with the findings of Irving et al.⁴ who reported that patients with intracanalicular tumors and tumors of less than 1.5 mm had better quality of life outcomes than patients with larger tumors, and Rigby et al.,¹² who found increasing disability in patients with larger tumors. TABLE I

Table TABLE I.. Significance of Preoperative Factors in Determining Health Status Outcome.

DISCUSSION

The traditional rationale for operating on patients with vestibular schwannoma, who usually have minimal functional deficit before surgery, is that with time, tumor growth is anticipated, and with increase in tumor size, the posttreatment surgical outcomes are worse. This view is supported by the technical measures of success that have been applied to vestibular schwannoma surgery such as postoperative facial nerve function and hearing preservation rates.^13-17 Better outcomes are associated with smaller tumor sizes. However, the findings of studies in which the patient's self-assessment of quality of life status is decreased after vestibular schwannoma surgery,^{5, 6} coupled with the knowledge that some tumors are static in size or have low growth rates,^18-21 are increasingly challenging this traditional operative rationale. The findings of this study supported by those of others^{1, 5, 6} that quality of life status is decreased in the majority of patients after surgical treatment suggest that there may be a place for a conservative policy in the management of patients with vestibular schwannoma. These findings are hardly surprising, however, as most patients vestibular schwannoma have few symptoms and minimal disability before surgery and treatment of vestibular schwannoma is aimed at dealing with the disease rather than patient symptoms per se. TABLE II

Table TABLE II.. SF-36 Scoring.

The second significant finding revealed by patient assessment of outcome in terms of quality of life, is that all eight domains shows no significant difference regardless of tumor size, operative approach, or patient age. Nikolopoulos et al.⁶ similarly found that tumor size did not affect postoperative quality of life, but younger patents had a poorer outcome than older patients. In contrast, Irvine et al.⁴ found that the outcome for intracanalicular tumors and tumors smaller than 1.5 mm was better than for larger tumors. Interestingly, this latter study was performed on a group of 227 patients operated on in the same unit, but before the patients surveyed in this study, suggesting that the improved results for the patients presenting with tumors of all sizes may be an effect of the surgeon's experience or reflect differences in questionnaire design that cannot be easily controlled for.

With increasingly early diagnosis, low tumor growth rates, and minimal preoperative functional deficits, a clinical dilemma regarding the timing of operative treatment of such patients is raised. If the narrow traditional technical measures of surgical outcome showing worse results with larger tumors are adopted as a guideline for the timing of vestibular schwannoma surgery, then operating on smaller tumors is justified, as had been concluded by Irvine et al.⁴ and Rigby et al.¹² Posed against this view is the findings of an increasing number of patient-centered assessments of outcome, such as this quality of life study and others,^{2, 3, 5, 6} that indicate a worse outcome after surgery; then the nonoperative management of patients with minimal functional deficits is supported.³ Both points of view have their proponents, but in the preoperative clinical setting all measures of surgical outcome after vestibular schwannoma surgery, whether technical or patient oriented, form guidelines as to the possible treatment options and possible outcomes for individual patients. In the ideal situation the best treatment option will ultimately be chosen by the well-informed patient based on the information provided to him by the treating clinician.

The way in which quality of life is defined and the methods by which it has been studied can be criticized from many points of view.^{22, 23} The surveyed patient population may be skewed^{1, 24} or the measurement tool used may be too condition specific^{2, 3} or inappropriate to capture the desired information.^{4, 11} The questionnaire used in this study may be more appropriate for measuring the quality of life in chronic static conditions such as back pain rather than the response to a surgical treatment, as we have attempted to document.^{8, 25} In addition, the very nature of questionnaire designs may render them insensitive to some of the more subtle and subjective as aspects of surgical treatment such as being cured from a worrying and potentially fatal pathology or the attention of sophisticated and expensive medical treatments being expended on them, resulting in a variety of conflicting conclusions. Two recent studies using relatively condition specific questionnaires^{24, 26} concluded that few patients experience negative social or life altering consequences following vestibular schwannoma surgery.

Despite these criticisms and possible limitations, this study and others that attempt to document and quantify health outcomes after vestibular schwannoma treatment from a patient point of view, form an increasingly important complement to the clinical information provided by traditional technical measures of surgical outcome. The SF36 questionnaire is a particularly usefully tool as it generality provides a contrast to the condition-specific measurement tools used by previous studies.

ACKNOWLEDGMENT

Acknowledgment is given to Dr. Brian Thom and Miss Sara Shore at the Center for Applied Medical Statistics for their statistical advice and Dr. Will Hollingsworth at the Institute of Public Health, University of Cambridge for help with standardizing the raw SF36 scores.