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Data from epidemiologic and mental health services research suggest that 50 to 60 percent of patients with mental illness in the United States are treated exclusively within the general medical care system (Regier et al. 1978; Shapiro et al. 1984). These findings stimulated Regier and colleagues (1978) to label primary care medicine a major part of the "de facto" mental health service of the United States. Since more severe disorders such as schizophrenia, manic depressive illness, and the personality disorders are preferentially referred to the mental health system, an even higher percentage of patients with anxiety and depression are treated exclusively in the general health care system, especially in primary care. The recent National Institute of Mental Health (NIMH) Epidemiologic Catchment Area (ECA) study demonstrated that over a 6-month period, 70 percent of patients with affective illness visited a general medical care clinic whereas only 20 percent visited a mental health professional (Shapiro et al. 1984).
Epidemiologic studies have found that from 25 to 33 percent of primary care patients suffer from a mental disorder diagnosable on a structured psychiatric interview (Hoeper et al. 1979; Bridges and Goldberg 1985). Perhaps another 20 percent have transient stress induced mental symptoms or chronic subclinical symptoms that do not meet research criteria, but are nonetheless associated with significant patient suffering and distress (Stoeckle et al. 1964).
Two decades of studies have demonstrated that, despite the high prevalence of mental illness in primary care patients, one-third to one-half of these psychiatric illnesses are not accurately diagnosed by their physicians (Nielson and Williams 1980; Schulberg et al. 1985; Katon 1987). Recent studies showed that somatization is the primary reason for this lack of diagnosis (Bridges and Goldberg 1985; Katon 1987). Somatization can be described as the presentation of psychosocial distress in an idiom of physical symptomatology and a coping style of increased health care utilization (Katon et al. 1984).
Mental illness is associated with amplification of chronic medical symptoms as well as psychophysiologic symptoms (headache, epigastric pain, insomnia). The tendency to amplify symptoms and the stigma of mental illness are the primary reasons that many patients present with somatic complaints when suffering from a mental illness. Bridges and Goldberg (1985) demonstrated that 95 percent of patients with anxiety and depression were correctly diagnosed when they described their psychologic distress as their presenting complaint. However, 48 percent of the patients with mental illness who presented with somatic complaints or complaints about their chronic medical illnesses were misdiagnosed or not accurately perceived to have a mental disorder by their primary care physicians.
Several researchers have shown that a small percentage of patients consume a major portion of health care. Collyer (1979) found that 3.6 percent of his primary care clinic population used 10 percent of his contacts and one-third of his time over a 1-year period. Katon and colleagues (1988b) found that 10 percent of enrollees in a large health maintenance organization used approximately one-third of all outpatient visits in an 18 month period, and that 20 percent used more than 50 percent of all outpatient visits. Furthermore, these patients were likely to sustain utilization well above normative levels. Prior research indicated that frequent users of health care are consistently found to have higher levels of psychologic distress, as well as poorer physical health status, than low utilizers (McFarland et al. 1985; Densen et al. 1959). Katon and colleagues (1988b) demonstrated that almost half of screened high utilizers (patients in the top 10 percent of 18 primary care physician panels) were psychologically distressed. Moreover, 58 percent of these distressed high utilizers had either a current DSM-III anxiety disorder (panic disorder or generalized anxiety) or affective disorder (major depression or dysthymic disorder).
Two studies found that anxiety represented the fifth and fifteenth, respectively, most common medical or psychiatric diagnoses in primary care (Valbona 1973; Marsland et al. 1976). Moreover, the 1980-81 National Ambulatory Medical Care Survey, which gathered information on approximately 90,000 patient visits to a nationally representative sample of private physicians from nine medical specialty groups, determined that anxiety and nervousness accounted for 11 percent of all visits to physicians. Other physiologic complaints often associated with severe anxiety were also reported frequently, such as headache and dizziness (11.2 percent) and abdominal or stomach pain (7.5 percent) (Schurman et al. 1985).
Further evidence of the prevalence of anxiety in medical patients was provided by a recent survey of 350 primary care physicians who rated anxiety disorders as the most common psychiatric problem seen in their clinics (Orleans et al. 1985). Antianxiety medications in general, and benzodiazepines in particular, have consistently been among the most frequently prescribed medications in the United States over the last 15 years, and more than 80 percent of these prescriptions were written by primary care physicians (Hollister 1980). One study showed that 18 percent of more than 1,500 randomly selected primary care patients in 15 group practices were prescribed minor tranquilizers during a 6-month period (Wells et al. 1986).
Not only is pathologic anxiety a primary reason for patients to visit physicians and a common etiology for psychophysiologic complaints, but it also represents a psychologic response to acute or chronic medical illness. Zung (1979) demonstrated that pathologic anxiety (defined as a score greater than 45 on the Zung Self-Rating Anxiety Scale) occurs in 9 percent of people in the community, 32 percent of patients seeking medical care from primary care physicians, and 52 percent of patients with a known cardiologic illness. Anxiety frequently causes patients to amplify complaints of organic illness and increase utilization of health care (Katon and Roy Byrne 1989). For example, Dirks and colleagues (1980) found that patients with asthma and severe anxiety had three times as many hospitalizations as asthmatic patients with similar degrees of physiologic asthma, but low levels of anxiety.
Studies of primary care patients with mental illness have shown that these patients use about twice as much nonpsychiatric medical care as patients without mental illness (Hankin and Oktay 1979). Thus, patients with mental illness are overrepresented among patients who actually use clinical care over a 1-year period. This makes it essential for primary care physicians to start to accurately diagnose and treat or refer these patients appropriately, to decrease patient suffering as well as to decrease the stress on physicians of primary care practice.
Early accurate recognition and treatment of mental illness may decrease somatization and maladaptive illness behavior in these patients (Bridges and Goldberg 1985). Somatization frequently leads to high clinical utilization and potential harm to patients through inappropriate or invasive use of medical technology as well as to dependence on health care providers to meet psycho-social needs redefined as health care needs (Katon et al. 1984).
This monograph focuses on the diagnosis and treatment of panic disorder, a subtype of anxiety that frequently affects primary care patients but is often not accurately diagnosed. The philosophy underlying this work is that enhanced accuracy of diagnosis of patients with panic disorder will lead to more effective and appropriate care for these patients. This monograph reviews the latest epidemiologic, psychobiologic, and treatment studies on panic disorder and clarifies the relationship between panic disorder and other common psychiatric illnesses, somatic symptoms, and medical illnesses.