Mental vs. Physical Illness: Diagnosis, Causes, and Treatment

Introduction: Beyond the Biomedical Model

For centuries, humans have tried to separate disease into a cause-and-effect, black-and-white frame of reference. Historically, disease was sometimes thought to be divinely inspired or carried in the wind. With the advent of the Scientific Revolution and the microscope, germ theory emerged: this germ (virus, bacteria, etc.) caused this disease, another caused that one. Germ theory has primarily been a Western paradigm, whereas in the East, disorders are typically understood as imbalances within one system or another. In the biomedical model, responsibility for illness is placed externally — because the germ is external — and illness is seen as confined to a specific organ or group of organs.

A newer model that combines both the physical and mental aspects of illness — the Health Psychology Model — acknowledges that yes, there are differences in symptoms, diagnosis, and care between mental and physical ailments, but that humans are holistic beings and that physical and mental disease each affects the other. It is this holistic continuum that truly defines the new model: it focuses on interaction, on holism, and less on simply identifying the cause of disease, and more on improving quality of life to prevent disease (Curtis, 2000). Based on this view, if we were to group disease, it should likely be grouped by affected region — with no sharp distinction between the mental and the physical, but rather as psychological disorders and/or physical disorders, with the understanding that there is almost always blurring between them (Dombeck, 2003).

Conditions that would now be called depression or mental illness were, for thousands of years, seen as physical manifestations of mania, hysteria, and melancholia, and were treated as if the disease were a physical cut or bruise. It is difficult to see hysteria or mania, but we can observe their results — the symptoms. Similarly, calming a patient with a sedative mitigates the symptoms but not the root cause. In the 20th century, tremendous progress was made toward a better understanding of the links between mental and physical ailments, as well as in the identification and treatment of both.

Assessment of Mental and Physical Disorders

In reality, neither minds nor bodies develop illness in isolation — only people do, within certain systems of the body. Mental illness can be brought about by trauma to the brain or body, but it can just as easily result from a chemical or biological imbalance. Physical illness may be brought on by mental and emotional causes — stress, grief, and trauma — and may manifest in ways that tie both dimensions together. Notably, the International Classification of Diseases, used by the World Health Organization and other international bodies, does not draw a fundamental distinction between mental and physical diseases; it simply categorizes conditions as aspects of either the psychiatric or the physical body (Kendall, 2001).

Assessment of physical disorders tends to be quantitative in nature, conducted through measurements and tests using established norms and their variations to identify illness. Blood pressure, pulse, and various blood tests, for instance, each have specific mathematical benchmarks. This quantitative data is combined with a thorough history of symptoms, and matching the symptoms with the data provides the tools for diagnosis. For mental disorders, assessment is more qualitative: clinicians evaluate an individual's mood, behavior, thinking patterns, reasoning, memory, and ability to express themselves and get along with others. This assessment is typically geared toward age appropriateness, so that a child's evaluation differs considerably from an adult's.

Diagnosis: Patterns, Symptoms, and Methods

At times, quantitative testing is also used to assess personality, cognitive function, and memory. In most cases, both physical and mental health are assessed during every visit to a physician, and various tools are used to probe for deeper answers (American Psychiatric Association Practice Guidelines, 2006).

The term diagnosis refers to the identification of the nature and cause of a condition. In both mental and physical illness, clinicians look for patterns of behavior, symptoms, and quantitative measurements, combined with a medical history. Diagnosis is usually symptom-driven: an initial clinical picture, combined with testing, forms a working opinion that is sometimes confirmed by laboratory results. For instance, a patient presenting with nausea, pain, depression, anxiety, and a yellowish skin tone may have blood tests reveal liver malfunction, leading to a diagnosis of hepatitis. In this case, both physical and mental symptoms are present, but the physical nature of the condition is diagnosed first.

For mental illness diagnosis, symptoms are equally important but are based more on how the individual functions within social systems or on direct observation of the patient's behavior (How Are Mental Illnesses Diagnosed?, 2012). Thus, both approaches use symptoms as a guide, but mental diagnosis is more empirical and observation-based, while physical diagnosis relies more heavily on quantitative measurements.