A physical disorder is often used as a term in contrast to a mental disorder, in an attempt to differentiate medical disorders that have an available mechanical test (such as chemical tests or brain scans), from those disorders which have no laboratory or imaging test, and are diagnosed only by behavioral syndrome

Syndrome

In medicine and psychology, a syndrome is the association of several clinically recognizable features, signs , symptoms , phenomena or characteristics that often occur together, so that the presence of one or more features alerts the physician to the possible presence of the others...

 (such as those in the Diagnostic and Statistical Manual of Mental Disorders

Diagnostic and Statistical Manual of Mental Disorders

The Diagnostic and Statistical Manual of Mental Disorders is published by the American Psychiatric Association and provides a common language and standard criteria for the classification of mental disorders...

 (DSM).

Differentiating physical disorders from mental disorders can be a difficult problem in both medicine and law, most notably because it delves into deep issues, and very old and unresolved arguments in philosophy and religion. Many materialists believe that all mental disorders are physical disorders of some kind, even if tests for them have not yet been developed (and it has been the case that some disorders once widely thought to be purely mental, are known to have physical origins, such as schizophrenia

Schizophrenia

Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...

). Some psychiatrists take the position that some or all mental disorders may be seen analogously to the information level of programming in a computer. In this case, all such disorders are associated with physical changes in the brain, but the pathology is at the level of brain information and programming (software), which is fundamentally separate from the means to store it.

Some recognized physical disorders produce significant behavioral changes. For example, fever

Fever

Fever is a common medical sign characterized by an elevation of temperature above the normal range of due to an increase in the body temperature regulatory set-point. This increase in set-point triggers increased muscle tone and shivering.As a person's temperature increases, there is, in...

, head trauma, and hyperthyroidism

Hyperthyroidism

Hyperthyroidism is the term for overactive tissue within the thyroid gland causing an overproduction of thyroid hormones . Hyperthyroidism is thus a cause of thyrotoxicosis, the clinical condition of increased thyroid hormones in the blood. Hyperthyroidism and thyrotoxicosis are not synonymous...

 can produce delirium

Delirium

Delirium or acute confusional state is a common and severe neuropsychiatric syndrome with core features of acute onset and fluctuating course, attentional deficits and generalized severe disorganization of behavior...

.