Front Matter

Psychiatric disorders are among the largest causes of disability in advanced industrial democracies. This stems from the fact that many psychiatric illnesses have an early onset, with many disorders beginning in childhood and adolescence, as well as the high prevalence of psychiatric illness (Murray et al. 2013). Even when low- and middle-income countries are included, psychiatric illness still has a significant and increasing burden in years of life lost to disability worldwide, with particularly a burden in younger individuals (Bloom et al. 2011).

In addition to this illness burden, patients with psychiatric illness, like their age-matched cohorts, have intercurrent general medical and neurological illness. While the rates of these comorbid illnesses vary by study and illness type, there is very robust evidence that patients with psychiatric illness, including substance abuse, experience early mortality, with life spans that are between 8 and 15 years shorter compared with age-matched control subjects (Walker et al. 2015). While a percentage of this early mortality is due to suicide or overdoses, the majority is due to increased rates of death from common medical conditions such as cardiac disease, respiratory illness, and malignancies. Metabolic syndrome may be a factor, particularly in relation to the effects of psychiatric medications, as is tobacco smoking (Schroeder and Morris 2010).

Another important reason that an understanding of the interaction between psychiatric and medical illness is useful is that the elderly population in the developed world is growing. The accrual of medical morbidity, let alone dementia, with aging will increase the incidence of medical-psychiatric comorbidity.

Patients with psychiatric illness use health services in different ways from their age-matched peers. In studies from both the United States and the United Kingdom (Dorning et al. 2015; Melek et al. 2014, 2018), patients with psychiatric illnesses were more likely than persons without mental disorders to use medical inpatient and emergency services, even for similar medical conditions, and more likely to be medically hospitalized for conditions or procedures usually treated in ambulatory care settings. In the aggregate, these patterns make the total cost of the care of patients with psychiatric illness more expensive, especially due to increased medical care utilization. A study commissioned by the American Psychiatric Association in 2014, conducted by the consulting and actuarial firm Milliman, found that the medical/surgical health care expenditures for patients who had utilized psychiatric services were two to three times higher than the expenditures for patients who did not use psychiatric services (Melek et al. 2014). In real dollar terms, the total cost of care per year was increased by $292 billion per year, driven by increased hospital-based care for medical surgical services. When Milliman repeated its study in 2017 (Melek et al. 2018), the increased cost had grown to $402 billion per year.

Regardless of their financial impact, psychiatric illnesses can affect the course of medical disorders and the way in which these disorders present in general care settings. Among the better known of these effects is the impact of major depressive disorder (MDD) on the mortality associated with a recent myocardial infarction. Numerous studies have shown higher rates of death from cardiovascular disease in patients who have MDD post–acute coronary syndromes (Lichtman et al. 2014). Of course, there are other psychiatric illnesses, including substance use, that are associated with impaired medical outcomes, including medical disorders such as liver disease, cardiomyopathy, endocarditis, and lung cancer. The impact of the current opioid epidemic and its interaction with other mental disorders and general medical mortality is highly significant (Case and Deaton 2015; Olfson et al. 2018). Lifestyle and behavioral contributions are risk factors for chronic illness, including late-life noncommunicable diseases (Murray et al. 2013).

Although we remain mindful of this broader context, in this textbook we primarily focus on a specific subsection of illnesses: medical disorders that can cause psychiatric symptoms. As young physicians, we became aware of these clinical presentations during our training. For one of us (P.S.), it was as an internal medicine resident in a busy academic medical center where a bevy of patients with delirium, agitation, hallucinations, or psychotic illness had other medical disorders that were causing their symptoms. Hepatic, metabolic, infectious, and neurological disorders were frequent. Young men with dysregulated behavior (either aggressive or overly placid) had brain injuries that were directly causative of their changed behavior. An older patient receiving high-dose intravenous steroids to prevent a transplant rejection presented in a new-onset manic state. An elderly woman with wide-based gait, incontinence, and abulic affect was found to have extensive white matter hypodensities on central nervous system imaging and a vascular depression responsive to antidepressants. Another woman thought to have a depression lacked cognitive changes or mood symptoms consistent with MDD. Her worsening weakness and motor difficulties were soon revealed as severe myasthenia gravis. For another one of us (D.A.S.), it was dual training in neurology and psychiatry that allowed the consideration of the interface between the medical and the psychiatric being mediated by brain disease. Among these clinical experiences, a considerable number involved patients with multiple sclerosis and pseudobulbar affect, epilepsy and postictal psychosis, Parkinson’s disease and panic attacks, and frontotemporal dementias with personality and behavior changes. In such cases, the diagnosis, management, and discussions with the patients and their families were all informed by a convergent neuropsychiatric view that transcends the typical neurological-psychiatric distinctions.

In all of these scenarios and in countless others that occur daily in hospitals, clinics, and doctor’s offices, patients present with psychiatric symptoms caused by their medical disorders. Psychiatric symptoms due to other medical conditions can be as complex and disabling as classic psychiatric illnesses whose etiology is unknown. The fact that psychiatric syndromes can be well-described sequelae of medical disorders is often unfamiliar to our patients, their families, and the general public. Because of their rarity, many of these syndromes may also be unfamiliar to physicians and other clinicians. Indeed, there is an older literature that suggests a tendency for physicians to underdiagnose medical disorders, whether causative or not, in patients with psychiatric illness (Hall et al. 1978; Koranyi 1979).

The proper and careful consideration of all of the medical issues facing patients with psychiatric symptoms is important for several reasons, but primarily because such an approach is good medical practice. The high comorbidity of psychiatric and medical disorders and the shortened longevity of patients with psychiatric illness make a comprehensive evaluation imperative—as does the importance of properly diagnosing, and thus treating, these medical causes of psychiatric symptoms.

There are other reasons for considering medical issues in patients with psychiatric symptoms. First, we tend to think of mental disorders as being mentally caused. Such a view is intrinsic to our language, which separates brain and mind and also contributes to the stigma of psychiatric illnesses, which are still too commonly thought to be due to moral failing or fault. The recognition of the medical factors, as well as what we typically think of as the biological or genetic factors, that cause these illnesses is thus important. Second, attention to these medical causes is important when considering the etiology of psychiatric syndromes that are not due to a specific medical disorder. These medical disorders can broaden our thinking about the mechanisms of psychiatric disorders whose causes are at present unknown. Inflammation, autoimmunity, and endocrine mechanisms can all point to causes of psychiatric illness that our leading pathophysiological models and science may not have considered. In some cases, these mechanisms may suggest a single underlying etiopathology that looks like a psychiatric-medical “comorbidity” but may instead represent a single disease process that manifests with medical symptoms in peripheral organ systems and with psychiatric symptoms in the brain. Neurological disorders are even more intertwined mechanistically, given the role of brain circuits in producing perception, cognition, emotion, and behavior. Here, the location of disease-induced circuit abnormalities has a significant influence on psychiatric symptomatology and informs models of neuropsychiatric disease.

In those clinical areas where there are fewer medical disorders that directly cause psychiatric illness, there are nevertheless complexities in the way in which medical or psychiatric disorders may be affected by comorbid illnesses. In some cases, this complexity may be the difficulty of assigning particular symptoms—for example, fatigue secondary to medical versus psychiatric causes. In other patients, the interaction will be the known impact of psychiatric illness on the course of a medical disorder or drug interactions that may directly affect medical or psychiatric management. Where relevant, these issues are highlighted in the chapters that follow. For many of these topics, there are not systematic or randomized data on particular conditions. Where more extensive data have been developed, we have endeavored to include them. Of course, as in any such text, not all disorders can be covered.

Patients present in clinical settings with specialized or chief concerns for the visit. They also bring the full range of their medical and personal histories to clinical encounters, even if these are not the focus of a particular clinical service. The specialization of medical practice, a problem decried as long ago as 1933 in the New England Journal of Medicine in a special issue on psychiatry (Noble 1933), risks seeing patients within the context of where they are evaluated rather than their clinical history or concerns. In many situations, such a focused perspective is beneficial to care; however, when a patient’s symptoms or course are atypical, a focused perspective may risk missing other causes of illness.

These issues are, if anything, more challenging in the evaluation of psychiatric symptoms and disorders. While our diagnostic precision has improved over the past 75 years, there is a high rate of comorbidity among psychiatric diagnoses, a lack of biological or imaging markers of many illnesses, and an unfortunate tendency for patients with psychiatric illness to have other medical complaints discounted. Additionally, for many diagnoses that depend on symptom clusters to generate syndromes, symptoms may be referable to bodily functions in a nonspecific fashion. Whether we are considering fatigue, tachycardia, or breathlessness, there is a risk that potentially causative medical symptoms are discounted—or, conversely, that an endless search for medical causation can miss a more obvious psychiatric disorder.

In neurological patients, psychiatric symptoms may be due to a co-occurring psychiatric illness, a response to disability, a medication, or involvement of brain regions or circuits mediating mental or behavioral functions. A number of these factors are often relevant in a single patient presentation. Not infrequently, it is the psychiatric disturbances (more than the other neurological ones) that most affect the patient and family, as well as their living situation. For this reason, we think it is essential to approach the evaluation and care of patients with a healthy dose of humility and a recognition that whatever our specialization—psychiatrist, internist, neurologist, or other—we need to keep an open mind about the patients we evaluate. That open mind can, in some cases, include reviewing or repeating laboratory or imaging studies, performing neurological or physical examinations, or being alert to loss, stress, and other psychological factors that may influence our patients’ symptoms. For many of us, good practice includes getting second opinions, additional consultations, or informal “curbside” advice from colleagues whose perspectives and expertise we trust. We likewise hope that this book can make accessible much of what we know, particularly regarding medical conditions that directly cause psychiatric disorders, and thus provide guidance when difficult clinical circumstances arise.

The book is divided into four parts. The first part, “Approach to the Patient,” focuses on the approach to the patient and special aspects of medical, neurological, and imaging/laboratory examination and testing. It includes perspectives from internists with particular training in clinical decision making on how they approach diagnostic uncertainty and from neurologists with deep clinical expertise in bedside and clinical evaluation. There are chapters that detail office-based or hospital cognitive testing and that provide an extensive overview of the uses of neuroimaging. There is also a chapter on both laboratory testing and toxicological syndromes.

The second part, “Psychiatric Considerations in Medical Disorders,” is organized by medical and neurological disorders. This is a section one would consult for a patient with a known medical or neurological disorder where the clinician is considering whether concomitant psychiatric symptoms are secondary to the medical illness or if there are challenges in the management of the medical and psychiatric symptoms. Some chapters—for example, those on neurological, endocrine, and inflammatory disorders, to name three—discuss conditions that have been directly linked to psychiatric presentations. Other chapters—for example, those on cardiovascular and renal disease—have fewer such conditions but include illnesses that have high co-occurrence with psychiatric disorders. There are often complex diagnostic and management issues that will bring patients with medical-psychiatric comorbidity to clinical attention.

The third part, “Medical Considerations in Psychiatric Disorders,” is organized from the perspective of psychiatric conditions. This section focuses on the major diagnostic categories and clinical presentations of psychiatric illness. Here the focus is on known medical causes of each domain of psychiatric illness, and this section can be consulted by clinicians when caring for a patient with a previously identified psychiatric presentation where there has been an increasing suspicion of a medical or neurological cause. This suspicion can occur when patients have atypical presentations, histories of traumatic brain injury or other neurological insult, or unexpected medical or neurological symptoms or findings or when patients fail to respond as expected to standard psychiatric care. Dementia and delirium, which in DSM-5 are categorized as Neurocognitive Disorders (American Psychiatric Association 2013), are included in this section as well.

The final part, “Conditions and Syndromes at the Medical–Psychiatric Boundary,” contains chapters on pain, insomnia, and somatic symptom and related disorders. Chronic pain and insomnia accompany many physical and mental conditions, and these chapters highlight the linkages of these symptoms to both medical and psychiatric disorders. Finally, a chapter on somatoform conditions is included. This describes a group of illnesses in which patients experience distressing bodily symptoms and functional impairment of uncertain etiology and often initially seek care for these symptoms in medical settings.

Whether patients have a known medical disorder and their clinicians are trying to assess the etiological importance of that disorder to their psychiatric symptoms, or a physician has a patient with a psychiatric presentation whose illness is atypical or nonresponsive to usual care, we hope that this text can serve as a reliable guide to what we know about these important conditions and how we may more effectively diagnose and care for our patients.