Psychosomatics 46:540-548, December 2005
doi: 10.1176/appi.psy.46.6.540
© 2005 Academy of Psychosomatic Medicine
Somatoform Disorders Among First-Time Referrals to a Neurology Service
Per Fink, M.D., Ph.D., D.M.Sc.,
Morten Steen Hansen, M.D., Ph.D., and
Lene Søndergaard, M.D.
Received Nov. 10, 2003; revision received Nov. 26, 2004; accepted Feb. 4, 2005. From the Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital; the Department of Psychiatric Demography, Psychiatric Hospital, Aarhus, Denmark; and the Department of Psychiatry, Vejle County Hospital, Vejle, Denmark. Address correspondence and reprint requests to Dr. Fink, Research Clinic for Functional Disorders and Psychosomatics, Aarhus University Hospital, Noerrebrogade 44, 8000 Aarhus C, Denmark; flip{at}as.aaa.dk (e-mail).
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ABSTRACT
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Consecutive new neurology inpatients and outpatients (N=198) were assessed for somatoform disorders by using the Schedules for Clinical Assessment in Neuropsychiatry. Sixty-one percent of the patients (59% of the female patients and 63% of the male patients) had at least one medically unexplained symptom, and 34.9% fulfilled the diagnostic criteria for an ICD-10 somatoform disorder (27.7% of the male patients, 41.3% of the female patients, 20.5% of the inpatients, and 43.2% of the outpatients). The prevalence figures were about the same when DSM-IV criteria for somatoform disorders were used. Of the patients with a somatoform disorder, 60.5% also had another mental disorder. Somatization disorder, somatoform autonomic dysfunction, pain disorder, and neurasthenia were equally prevalent (6%–7%); dissociative (conversion) disorders and undifferentiated somatoform disorders were found in 2–3% of the patients. Fifty percent of the patients with somatoform disorders were identified by the neurologists.
Key Words: Somatoform disorders • prevalence • neurological patients • comorbidity • recognition • neurasthenia • chronic fatigue syndrome • medically unexplained symptoms
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INTRODUCTION
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Mental disorders are highly prevalent among patients attending neurological services.1–6 Patients presenting with physical symptoms not attributable to any known medical condition (i.e., functional or medically unexplained symptoms) are particularly common.3,4,6–8 In ICD-10 and DSM-IV these conditions are classified mainly in the somatoform disorders group. In a study that used the same data set used in this study, somatoform disorders were the most prevalent psychiatric diagnoses among neurological inpatients and outpatients.4 Little is known about the symptoms and types of somatoform disorders experienced by patients in neurological settings. In studies that have been conducted in this area, ICD-10 or DSM-IV criteria have not been used, or only one or a few of the diagnostic subcategories in the somatoform disorders group and not the whole diagnostic spectrum have been investigated.
The aims of this study were to determine the prevalence of medically unexplained symptoms and of somatoform and related disorders (classified according to ICD-10 and DSM-IV diagnostic subcategories) among new inpatients and outpatients seen in a neurological setting, determine the comorbidity of these disorders with other mental disorders, and assess whether somatoform and related disorders are diagnosed by neurologists.
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METHOD
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Inclusion
The study population included consecutive patients age 18 years or older referred for the first time to the neurological department of Vejle County Hospital, Vejle, Denmark, during a 3-month period in 1997. Only patients who had never previously been examined by a neurologist were eligible. The department provides all hospital-based neurological services for the general population of Vejle County, a total of approximately 356,000 inhabitants. The county is a mixed rural and urban area with four fairly large towns in which about one-half of the population is middle class. In total 290 patients were admitted either as inpatients or outpatients for the first time during the inclusion period (Figure 1). Excluded according to predefined criteria were patients who were not of Scandinavian origin (N=5) and patients who could not be interviewed because they were too ill (N=13) or because of deafness (N=4), somnolence (N=5), unconsciousness (N=3), aphasia (N=8), or disorientation (N=3). In addition, 11 patients were discharged before a research worker could contact them. Forty patients refused to participate in the investigation. Thus, 198 patients were included.
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FIGURE 1. Sample Selection in a Study of Somatoform Disorders Among New Patients Seen in a Neurology Service
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The excluded patients were compared to the included patients on age, gender, and use of psychiatric and nonpsychiatric health care. These analyses, reported in a previous study,4 showed only minor differences.
Table 1 summarizes the study subjects’ sociodemographic and admission characteristics, and Table 2 lists their ICD-10 discharge diagnoses.
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TABLE 1. Sociodemographic and Admission Characteristics of 198 New Patients Seen in a Neurology Service Over a 3-Month Period and Assessed for Somatoform Disorders
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TABLE 2. ICD-10 Discharge Diagnoses of 198 New Patients Seen in a Neurology Service Over a 3-Month Period and Assessed for Somatoform Disordersa
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Procedure and Assessment
A two-phase design was used. At admission or first contact, all patients were interviewed by one of two research nurses. The interview included an eight-item version of the Symptom Check List (SCL-8d),9 used to assess anxiety and depression, and the seven-item Whiteley index, which was slightly modified for use in the interview (available from the author on request). This scale measures illness worry and convictions about the presence of illness and has been shown to detect somatization.10 The responses to each item were dichotomized.
Patients were selected in the following manner to undergo a diagnostic psychiatric interview. Patients with a score of 2 or more on the SCL-8d and/or 3 or more on the seven-item Whiteley index were considered high scorers. A random sample consisting of 50% of all patients was selected for psychiatric interview, and of the remaining 50% of patients, all high scorers were selected for the interview. Thus, a stratified subsample consisting of all patients with high scores and approximately one-half of the patients with low scores was selected. The psychiatric interview was conducted either during admission or at the first visit in the outpatient clinic. If the patient could not be interviewed in these settings, an appointment was made for the interview to take place as soon as possible after the first visit. Of the 130 patients selected for psychiatric interview, 10 refused to participate. Thus, 120 patients were interviewed.
The psychiatric interview was conducted with the Schedules for Clinical Assessment in Neuropsychiatry, version 2.1 (SCAN).11 The SCAN interview is used to inquire about 76 physical symptoms in seven symptom groups. Each symptom is rated by the interviewer according to whether it can be attributed to a medical condition/dysfunction or not. Symptoms for which this distinction cannot be made reliably are rated with a separate code. In this study, we included in the analysis only those symptoms that were rated "definitely unexplained." The interviewers were free to explore aspects that were not fully clarified in the interview (e.g., by reviewing medical records or discharge letters). The interviewers met regularly during the course of the study to confer about specific cases and to discuss strategies for interpreting and rating ambiguous responses and symptoms that seemed to fall between the response categories. They were free to consult other physicians. The two SCAN interviewers, who had received psychiatric training during residency and who had been trained and certified at the World Health Organization center in Aarhus, were blinded to the patients’ answers to the interview at the index contact. The interrater agreement was high (agreement on 16 of 17 patients;  =0.88).
The SCAN interviews were used to develop computerized ICD-10 and DSM-IV diagnoses of somatoform disorders. At first contact and at discharge, the neurologist responsible for the examination/treatment of each patient was asked to rate whether the patient’s symptoms were functional (i.e., without any adequate organic base); this rating was made on a 5-point scale ranging from "definitely not" to "definitely yes." The neurologist was also asked to rate whether the patient was more preoccupied with his or her symptoms than would be expected on the basis of the nature of those symptoms; this rating was made on a 4-point scale ranging from "definitely not" to "yes, very much." Furthermore, at discharge only, the neurologist used a 4-point scale ranging from "no" to "markedly" to rate whether the patient had exaggerated his or her symptoms.
Data Analysis
Data from the second phase of the two-phase design were analyzed by using weights that were inversely proportional to the sampling probabilities.12,13 Prevalence estimates and approximate confidence intervals were calculated by weighted logistic regression analysis. The same method was used to estimate the associations between psychiatric disorders and other variables. In a few analyses we applied other statistical procedures using the same weights. In order to ensure valid standard errors and significance tests, the weights were scaled so that the sum of the weights was equal to the actual sample size (N=120). SPSS for Windows, versions 6.1.3 and 10 (SPSS, Inc., Chicago), was used for statistical analysis.
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RESULTS
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Somatoform Disorders and Functional Symptoms
Sixty-one percent of the patients (59% of the female patients and 63% of the male patients) had at least one medically unexplained symptom. Figure 2 shows the symptom frequencies. Symptoms associated with other organ systems were as frequent as neurological symptoms. About 35% of the patients fulfilled the diagnostic criteria for an ICD-10 somatoform disorder, and the prevalence was about the same when DSM-IV criteria were applied (Table 3). As for the specified ICD-10 diagnoses, somatization disorder, somatoform autonomic dysfunction, pain disorder, and neurasthenia were equally prevalent (found in 6%–7% of patients); dissociative (conversion) disorders and undifferentiated somatoform disorders were found in 2–3% of the patients. The distribution of diagnoses was quite different when the DSM-IV criteria were used: somatization disorder was much less common (2%), and pain disorder was more common (11.6%). DSM-IV undifferentiated somatoform disorder was much more frequent than ICD-10 undifferentiated somatoform disorder (Table 3). Conversion disorder (2.9%) was equally prevalent according to both diagnostic systems. ICD-10 hypochondriasis was rare (0.6%), and DSM-IV hypochondriasis was more common (1.8%). Somatoform disorder not otherwise specified was diagnosed in 12.8% of the patients according to the ICD-10 criteria and in 7.1% of patients according to the DSM-IV criteria. As Figure 2 shows, only few patients complained of urogenital symptoms (apart from sexual indifference), and this low frequency may explain the low prevalence of DSM-IV somatization disorder, compared with ICD-10 somatization disorder.
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FIGURE 2. Frequency of Medically Unexplained Symptoms Among New Patients Seen in a Neurology Service Over a 3-Month Period and Interviewed With the Schedules for Clinical Assessment in Neuropsychiatry (N=120)
aPercentage of female patients (N=69).
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TABLE 3. Prevalence of ICD-10 and DSM-IV Somatoform Disorders Among New Patients Seen in a Neurology Service Over a 3-Month Perioda
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Somatoform Disorders, Age, and Gender
The overall prevalence of ICD-10 (and DSM–IV) somatoform disorders was more than 10% higher among women than among men (Table 3). Adjusted for age, the gender difference was not statistically significant at a 5% probability level (p=0.10; weighted logistic regression). Women had a higher prevalence of all the specified ICD-10 and DSM-IV diagnoses, except for neurasthenia (Table 3). Figure 3 shows the overall prevalence of somatoform disorders among female and male patients in three age groups. The prevalence among male patients fell markedly with increasing age (p=0.02; test for trend in proportions). In the >60-year age group, the difference between genders in prevalence was 29.5%, but because of the small number of individuals, the difference did not reach statistical significance at a 5% probability level (p=0.06; weighted logistic regression).
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FIGURE 3. Prevalence of Somatoform Disorders Among New Patients Seen in a Neurology Service Over a 3-Month Period (N=198), by Gender and Age of Patients
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Somatoform Disorders Among Inpatients and Outpatients
Most ICD-10 and DSM-IV diagnoses had a higher prevalence among outpatients than among inpatients, but the differences were statistically significant for only a few categories. ICD-10 and DSM-IV somatoform disorders were more than twice as prevalent among outpatients as among inpatients (p<0.02; weighted logistic regression) (Table 3). This difference was partly accounted for by a higher prevalence of ICD-10 unspecified somatoform disorder among outpatients, compared to inpatients (p=0.03; weighted logistic regression) and a higher prevalence of DSM-IV undifferentiated somatoform disorder among outpatients, compared to inpatients (p=0.01; weighted logistic regression).
Comorbidity With Psychiatric Disorders
Table 3 reports rates of psychiatric comorbidity in the study subjects, i.e., the percentage of patients with a somatoform disorder who also had another ICD-10 mental disorder according to the SCAN interview. The overall rate of comorbidity was about 60%. The rate was higher in patients with some somatoform disorders and was lower in patients with other disorders, such as ICD-10 pain disorder (43.8%) and ICD-10 somatoform disorder, unspecified (39.6%). Several diagnoses, including four ICD-10 diagnoses and three DSM-IV diagnoses, had a comorbidity of 100%, i.e., all patients with these disorders had a comorbid psychiatric disorder. About one-quarter of the patients with a somatoform disorder had comorbid depression or anxiety disorder, but there was a large variation between the diagnostic subcategories. This variation may be artificial because of the relatively small patient sample.
Neurologists’ Impressions of Patients’ Symptoms and Symptom Preoccupation
None of the neurologists’ ratings of the functionality of patients’ symptoms, patients’ preoccupation with symptoms, or aggravation of symptoms identified all patients with somatoform disorders (Table 4). The question that identified the most somatoform patients was whether the patient was preoccupied with his or her symptoms. At the first contact, 50% of the patients with somatoform disorder were identified by the neurologists as at least "a little preoccupied"; 42% of the patients were so identified at discharge.
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TABLE 4. Sensitivity and Specificity of Neurologists’ Identification of Somatoform Disorders Among 198 New Patients Seen in a Neurology Servicea
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Only three patients with somatoform disorder (1.5% of all patients) were referred to a psychiatrist or psychologist. All three patients were, prior to admission, in treatment by their family physician for a mental disturbance.
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DISCUSSION
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About one-third of new patients seen in a neurological service over a 3-month period fulfilled ICD-10 and DSM-IV criteria for a somatoform disorder. We are not aware of other reports on the prevalence of ICD-10 and DSM-IV somatoform disorders among neurology patients. The prevalence of somatoform disorders identified in this study was higher than that found by Fink et al.14 among medical inpatients. However, in contrast to the previous study, the current study included only new patients, and the sample was younger and included both inpatients and outpatients. The divergence may therefore be partly explained by the different patient samples. The findings of a higher prevalence of somatoform disorders among women and among younger patients are in accordance with previous findings for medical inpatients.14 The prevalence of somatoform disorders in the current study was higher than that found for primary care patients in an earlier study.15
We used a two-step design that included interviews with all patients who scored high on the screening instruments and with a random sample of the remaining patients. This procedure was cost-effective because it allowed us to avoid interviewing numerous patients without mental problems. One weakness of the procedure is that the statistical weighting procedures used for correction of the skewness imposed by the sampling procedure weakened the statistical power and resulted in wide confidence intervals.
Considering solely functional or medically unexplained symptoms, the prevalence was higher in the current study, compared to other studies in neurological settings.3,7,16,17 The difference may be attributed to the fact that the other studies were based only on neurologists’ judgments. Neurologists may be inclined to focus mainly on the symptoms that they believe are relevant for the particular patient. In this study we systematically asked about all kinds of symptoms, regardless of the relevance for the actual neurological referral. Some patients might thus have had a well-defined neurological disease besides their somatoform disorder. We do not know whether this difference may partly explain the neurologists’ low rate of recognition of somatoform disorders, compared to the SCAN psychiatric interview, because we did not record whether the functional symptoms were the only reason for the neurological referral. Another explanation for the low level of agreement between neurologists’ impressions and the psychiatric interview findings may be that the concepts of medically unexplained symptoms and somatoform disorders are largely unfamiliar to or even neglected by neurologists. Finally, the prevalence of somatoform disorders may be overestimated. Symptoms rated as medically unexplained in the SCAN interview may indeed not have been so. However, as the interviewers were free to explore case notes and other information and the interview was carried out after the neurological examination, the findings of the neurological examination were taken into account by the interviewers. Both interviewers had had several years of training in medicine and surgery, and the one who did the main part of the interview had 1 year of training in neurology. To qualify for a somatoform disorder diagnosis, patients must have had symptoms for more than 6 months and must have had a substantial number of functional symptoms. (The second criterion applies to all somatoform disorder diagnoses except for unspecified somatoform disorder and pain disorder.) The diagnoses obtained by means of the SCAN interview thus seem substantial. The neurologists had high specificity in identifying patients with somatoform disorder, i.e., when they identified a functional disorder in a patient, that patient in most cases also received a somatoform disorder diagnosis according to the SCAN interview. This finding calls for more intensive study of the cases in which there were disagreement between the neurologists and the research interviewers.
No patient follow-up was conducted in our study, although follow-up data could have been used to investigate whether the symptoms were later explained by a differential diagnosis and to study the stability of the somatoform disorder diagnoses over time. However, medically unexplained symptoms only rarely are explained by a medical condition diagnosed at a later stage. For example, Crimlisk et al.18 showed that at 6-year follow-up only 2%–3% of patients discharged from a neurological department with a diagnosis of functional paralysis had an organic neurological disorder that fully or partly explained their previous symptoms.
Only three (1.5%) of the 198 patients in this study were referred to a psychiatrist or to a psychologist, and all three had a somatoform disorder according to the SCAN interview. The low referral rate in the present study is in line with findings in other studies.19 As the neurologists were able to identify many more than three of the patients with somatoform disorders, the low referral rate is not explained only by a lack of recognition of the disorders. Other factors such as lack of accessibility to psychiatric assistance, fear of stigmatizing the patient, or time pressure may be more important.
The findings of a high prevalence of functional complaints and somatoform disorders among neurology patients highlight the need for increased awareness of the problem among neurologists and for more research on the management of somatoform disorders.
The high rate of comorbidity between somatoform disorders and other mental disorders is in accordance with findings in other studies.14,15,20 Despite agreement on the overall prevalence of somatoform disorders assessed according to the ICD-10 and DSM-IV diagnostic systems, there were great discrepancies in the prevalence of the specific somatoform disorder subcategories according to the two systems. This pattern raises doubts about the credibility of the diagnostic subcategories, which may be one reason why neurologists are reluctant to adopt these categories in their diagnostic practice. It is therefore very important that the diagnostic groups be validated and revised on an empirical basis to make them acceptable for use in clinical practice.
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ACKNOWLEDGMENTS
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The study was supported by grants from Lundbeck A/S, the Foundation for Medical Research in Vejle County, and the Foundation for Research in Mental Disorders, Aarhus University.
The authors thank Dr. Aksel Bertelsen for help with the SCAN; Karsten Ellemann, Nina Rand, and Kirsten Kofoed for their contribution to data collection; staff members of the Department of Neurology, Vejle County Hospital, for help during data collection; and Søren Skadhede for assistance with data processing.
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ABSTRACT
INTRODUCTION
