Mental Disorders Due to Another Medical Condition

Primary Mental Disorders

The determination of direct physiological causality is a complex issue. Box 21-2 summarizes features that should raise the clinician's suspicion of medical causation of psychiatric symptoms. The onset of psychiatric symptoms that coincides with the onset (or increased severity) of the medical condition is suggestive, but correlation does not prove causation. Mental and other medical disorders may merely co-exist. The initial presentation of a medical condition may be psychiatric (e.g., depression that manifests before the diagnostic awareness of pancreatic carcinoma), or the psychiatric symptoms may be disproportionate to the medical severity (e.g., irritability in patients with negligible sensorimotor symptoms of multiple sclerosis [MS]). It also happens that psychiatric symptoms may occur long after the onset of medical illness (e.g., psychosis that develops after years of epilepsy). Psychiatric improvement that coincides with treatment of the medical condition supports a causal relationship, although psychiatric symptoms that do not clear with resolution of the medical condition do not rule out causation (e.g., depression that persists beyond normalization of hypothyroidism). There are also mental disorders DTAMC that respond to, and require, direct treatment (e.g., inter-ictal depression), which should not be interpreted as evidence of a primary mental disorder.

Psychiatric presentations uncharacteristic of primary mental disorders should raise the suspicion of a direct physiological effect of a medical condition. Features to consider include the age of onset (e.g., new-onset panic disorder in an elderly man), the usual time course (e.g., abrupt onset of depression), and exaggerated or unusual features of related symptoms (e.g., severe cognitive dysfunction with otherwise mild depressive symptoms). On the other hand, the typical features of a psychiatric syndrome support the likelihood that medical and mental disorders are co-morbid, but not causative. Such typical features include a history of similar episodes without the co-occurrence of the medical condition, as well as a family history of the mental disorder.

Scientific standards in medical literature have established probable medical causality for certain psychiatric symptoms that are more prevalent in certain medical conditions than the base rate experienced by an appropriate control group. There may also be a pathophysiological explanation for the psychiatric symptoms, based on the medical disorder, metabolic perturbation, or location of brain pathology (e.g., disinhibition or decreased executive function with frontal lobe damage). Such connections should be considered suggestive, but not definitive. Every patient's symptoms should be individually scrutinized. In the absence of large studies or historically-accepted connections, case studies or small series may support a causal relationship. While mildly helpful, these less stringent reports should be met with some skepticism.

Substance-induced Disorders

Many types of substances have the potential for use, misuse, or abuse. In considering the possible role of substances, clinicians should think in broad terms, and they should ask specifically about over-the-counter medications, herbal (natural or dietary) supplements, prescription medications (not necessarily prescribed for the patient), and alcohol and recreational (i.e., illegal) drugs. This detail should be routine in every evaluation, with the more selective use of blood or urine toxicology, as indicated. Symptoms may derive from substance use, intoxication, or withdrawal, and such mental symptoms may persist for several weeks after the patient's last use of the substance. Substance-induced mental symptoms are not necessarily evidence of misuse or abuse. Some medications may cause symptoms when used in therapeutic doses. When such symptoms resemble concomitant disease symptoms (e.g., when a patient with systemic lupus erythematosus [SLE] develops mood lability and is on steroids), it is possible that the symptoms are both substance-induced and DTAMC, in which case the clinician should code both conditions.

The “unspecified” categories in DSM-5 are reserved for symptoms characteristic of the given mental disorder (e.g., unspecified depressive disorder, unspecified neurocognitive disorder) “that cause clinically-significant distress or impairment in social, occupational or other important areas of functioning predominate but do not meet the full criteria” for any of the disorders in the identified diagnostic class, and where there is etiological uncertainty or insufficient information to make a more specific diagnosis.

Another Medical Condition

ANotherMEDICalCONDITion ( Box 21-3 ) is a mnemonic for the wide range of medical conditions that may result in psychiatric syndromes.

Infectious Diseases

The increased prevalence of immune suppression (e.g., from acquired immunodeficiency syndrome [AIDS], or from therapeutic suppression in cancer treatment or organ transplantation) has been associated with a concomitant increase in the chronic meningitides and other central nervous system (CNS) infections.

Herpes Simplex Virus ( Figure 21-1 )

Herpes simplex virus (HSV) is the most frequent etiology of focal encephalopathy, and may cause either simple or complex partial seizures. With a predilection for the temporal and inferomedial frontal lobes, as illustrated in Figure 21-2 , HSV is well known to cause gustatory or olfactory hallucinations, or anosmia (loss of the sense of smell). This concentration in limbic structures may also explain the personality change, bizarre behavior, and psychotic symptoms that some affected patients exhibit. Such personality changes, cognitive difficulties, and affective lability may be persistent. HSV-1 is responsible for most non-neonatal cases of HSV encephalitis, which does not appear to be more prevalent in the immunosuppressed population. However, HSV-2, which more commonly causes aseptic meningitis in adults, can cause encephalitis during the course of disseminated disease in immunocompromised adults.

Human Immunodeficiency Virus ( Figure 21-3 )

Patients with human immunodeficiency virus (HIV) infection experience a broad range of neuropsychiatric symptoms, collectively referred to as HIV-associated neurocognitive disorders (HAND). For descriptive purposes, these disorders have been further broken down into three recognizable conditions: HIV-associated dementia (HAD); HIV-associated mild neurocognitive disorder (MND); and asymptomatic neurocognitive impairment (ANI). Early cognitive and motor deficits involve attention, concentration, visuospatial performance, fine motor control, coordination, and speed. The subcortical type of dementia, characterized by short-term memory problems, word-finding difficulty, and executive dysfunction, is now rare (2%) in the US. Problems with sleep and anxiety are prevalent in the HIV-infected population. This is thought to be the result of wide-spread antiretroviral therapy, although some antiretrovirals have themselves been implicated as neurotoxins (e.g., efavirenz). There may also be depressed mood and an array of associated symptoms that resemble the neurovegetative symptoms of depression (e.g., apathy, fatigue, social withdrawal, and a lack of motivation or spontaneity). Mania and hypomania occur, though less frequently. New-onset psychosis is uncommon and generally seen only in advanced stages of disease, at which point patients may also develop seizures, agitation, severe disinhibition, and mutism.

The causes of HIV-related neuropsychiatric symptoms are as varied as the manifestations. Direct CNS infection, metabolic perturbations, endocrine abnormalities, malignancies, opportunistic infections, and the side effects of medications may all contribute. A consistent correlation has not been shown between the presence, severity, or location of CNS pathology and symptomatology. New onset and a CD4 count of less than 600 increase the likelihood that psychiatric symptoms may be due to HIV infection ( Figure 21-4 ), or to some other (HIV-related) cause (i.e., not due to a primary mental disorder).