Etiology and Pathophysiology
How do psychological factors affect medical illnesses? Physi-cians have long recognized that psychological factors seem to affect medical illnesses, and research elucidating the interven-ing causal mechanisms is now rapidly growing. From their clini-cal experience, physicians recognize many ways in which psy- chological factors affect the onset, progression and outcome of their patients’ illnesses. First, psychological factors may promote other known risks for medical illness. Smoking is a risk factor for heart disease, cancer and pulmonary and many other diseases, and individuals with schizophrenia or depression are much more likely to smoke than the general population. A wide variety of psychiatric illnesses are associated with an increased likelihood of abuse of other substances. Depression and schizophrenia are also associated with a sedentary lifestyle. Patients with affective disorders often have chronic pain and chronically tend to overuse analgesics. Individuals with schizophrenia, bipolar disorder and some personality disorders are more likely to engage in unsafe sex, which in turn increases the risk of sexually transmitted dis-eases, including HIV infection and hepatitis B. Depression, eat-ing disorders and other emotional and behavioral factors affect the pattern and content of diet.
In addition to promoting known risk factors for medical illness, psychological factors also have an impact on the course of illness by influencing how patients respond to their symp-toms, including whether and how they seek care. For example, the defense mechanism of denial may lead an individual to ig-nore anginal chest pain, attribute it to indigestion, delay seeking medical attention, or minimize the pain when describing it to a physician. This tends to result in treatment delay after the acute onset of coronary symptoms, with consequently greater morbid-ity and mortality. Anxiety is also a common cause of avoidance or delay of health care; phobic fears of needles, sight of blood, surgery and other health care phobias are common. Patients may also neglect their symptoms and fail promptly to seek medical care because of depression, psychosis, or personality traits (e.g., procrastination).
Psychological factors also affect the course of illness through their effects on the physician–patient relationship, since they influence both patients’ health behaviors and physicians’ diagnostic and treatment decisions. A substantial proportion of the excess mortality experienced by individuals with mental disorders is explained by their receiving poorer quality medical care (Druss et al., 2001a). One explanation for the poorer qual-ity and outcomes of medical care in patients with both serious medical and mental illnesses is the lack of integration between their medical and mental health care (Druss et al., 2001b). Psy-chological factors can also reduce a patient’s compliance with diagnostic recommendations, treatment and lifestyle change, and can interfere with rehabilitation through impairment of mo-tivation, understanding, optimism, or tolerance. A recent meta-analysis found that patients with depression are three times as likely to be noncompliant with medical treatment than patients without (DiMatteo et al., 2000). In addition, many of the effects of psychological factors on medical illness appear to be mediated through a wide array of social factors, including social support, job strain, disadvantaged socioeconomic and educational status, and marital stress.
There is an increasing body of scientific evidence that psychological factors, in addition to their impact on classic (nonpsychological) risk factors, patient behaviors and the phy-sician–patient interaction, have direct effects on pathophysi-ological processes. For example, stress has been experimentally shown to cause myocardial ischemia in patients with coronary disease. Stress and depression are associated with a wide range of immunological effects. Many psychiatric disorders (especially mood disorders) are associated with disruptions in homeostasis including sleep architecture, other circadian rhythms, and endocrine secretion and feedback. For example, depression causes increased bone remodeling and decreased bone density (Herran et al., 2000). That such effects occur is well established, but the magnitude of their clinical significance in medical dis-ease is often unclear, and full explanatory causal linkages have for the most part not been demonstrated yet. Nevertheless, inves-tigators have learned a great deal about changes in autonomic, hematologic, endocrine, immunologic and sensory function, as well as gene expression that bring us closer to understanding how psychological factors may affect medical illness.