There are three main types of disease etiologies that will be expounded upon in this lesson. These categories of disease etiologies are intrinsic etiology, extrinsic etiology, and idiopathic etiology.
Intrinsic Etiology
Intrinsic etiology means that diseases are caused by an internal source within the person. Examples of intrinsic etiologies of diseases include: genetic disorders, certain types of cancers or neoplastic disorders, endocrine or metabolic disorders, or diseases that affect the immune system.
Heritable factors, which includes genetic problems passed on from previous generations. Diseases of intrinsic etiology can include conditions such as phenylketonuria (PKU), Sickle Cell Anemia, and Tay Sachs Disease. Many of these types of diseases have no current cure.
Certain cancers and neoplastic disorders are also diseases of extrinsic etiology. Both neoplastic disorders and cancer result in abnormal cell growth. Neoplastic disorders can be either benign (and not harmful to the diagnosed individual) or malignant (harmful to the individual).
Endocrine and metabolic problems can also lead to intrinsic etiologies of diseases. The endocrine system produces hormones, which act as chemical messengers, and hormonal issues can lead to certain diseases. For example, Grave's Disease, also known as hypothyroidism, is an endocrine disease which is caused by an underactive thyroid. Diabetes is another medical condition that falls under the umbrella of metabolic and endocrine disorders.
Issues that contribute to problems with the human immune system are also considered diseases of intrinsic etiology. Both seasonal and food allergies are conditions that fall into this particular category regarding diseases of intrinsic etiology. Both conditions contribute to the production of antibodies for substances that are typically harmless to the average and unaffected person.
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Extrinsic Etiology
Extrinsic etiology refers to causes of disease which are originally found outside of the body of a human. An example of an etiologic agent responsible for a disease of extrinsic etiology would be the rhinovirus, which causes the common cold. Other diseases of extrinsic etiology include: infectious illnesses, animal bites/stings, exposure to radiation/chemicals/electricity, or diseases of iatrogenic nature.
Infectious diseases are conditions that result from extrinsic etiologies. This includes diseases caused by bacteria, fungi, viruses, and other types of pathogens. These illnesses may be spread person-to-person or may result from exposure to infected animals or objects.
Stings or bites from insects or other animals can pose as extrinsic etiologies of certain diseases. While the bite of a mosquito contributes to an itchy bump that usually disappears after a few days, sometimes a more severe problem can occur. The female Anopheles mosquito carries the "Plasmodium" protist which can cause the disease malaria. Regardless of whether one suffers from an itch for a few days, or a transmittable disease that can result in death, these conditions are both of extrinsic etiological nature.
Other entities that can contribute to diseases of extrinsic etiology include chemicals, radiation, and electricity. Some chemicals, including aromatic hydrocarbons, can cause certain cancers, other forms of disease, or damage to vital organs and/or tissues. For example, the carcinogenic chemicals found in tobacco can pose as and extrinsic etiology of certain cancers, including lung and esophageal cancers.
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A disease that has an iatrogenic cause is one that is caused by either medical assessment or intervention. An example of an iatrogenic cause of illness would be the side effects of undergoing chemotherapy and radiation to treat cancer. Oftentimes, a disease or illness that is caused in the hospital setting is referred to as a nosocomial illness. Nosocomial illnesses are not present in patients when admitted to the hospital but are caused during the hospital stay of the patient. An example of a nosocomial infection would be a female patient who becomes ill with a urinary tract infection after having a catheter placed in order to undergo an internal ultrasound. Nosocomial infections are considered types of iatrogenic causes of disease.
Idiopathic Etiology
A disease of idiopathic etiology is an illness unknown cause or origin. Conditions of idiopathic etiology may or may not be diagnosable and treatable, depending on the disease. An example of this type of disease is idiopathic pulmonary fibrosis.
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