How an Organic Disease Differs From a Functional Disorder

Organic disease is the term used to describe any health condition in which there is an observable and measurable disease process, such as inflammation or tissue damage. An organic disease is one that can be validated and quantified through the standardized biological measures known as biomarkers.

Doctor checking X-Ray with patient
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As opposed to a non-organic (functional) disorder, an organic disease is one in which there are detectable physical or biochemical changes within the cells, tissues, or organs of the body. A non-organic disease, by contrast, is one which manifests with symptoms but whose disease process is either unknown or unable to be measured by current scientific means.

Examples of Organic Disease

The term organic disease is an umbrella classification for many different types of illness. They can be localized (meaning they affect a specific part of the body) or systemic (affecting multiple organ systems). They can be inherited or caused by external or environmental forces. Some organic diseases are communicable, passed from one person to the next, while others are non-communicable.

Some of the broader categories and types of organic diseases include:

    • Autoimmune diseases in which the body's immune system attacks its own cells and tissues, such as:
      Type 1 diabetes
    • Multiple sclerosis (MS)
    • Rheumatoid arthritis
    • Lupus
    • Psoriasis
    • Cancer in which abnormal cells multiply unchecked and overtake healthy cells, such as:
      Breast cancer
    • Melanoma
    • Leukemia
    • Lymphoma
    • Lung cancer
    • Colorectal cancer
    • Inflammatory diseases which cause acute or progressive damage to cells and tissues, such as:
    • Pelvic inflammatory disease (PID)
    • Viral meningitis
    • Atherosclerosis
    • Fibromyalgia
    • Infectious diseases in which a bacteria, virus, fungus, parasite, or other microbe is transmitted between individuals, such as:
    • Hepatitis C
    • Zika virus
    • Tuberculosis
    • Influenza

Examples of Functional Disorders

A non-organic disease is typically referred to as being functional, meaning that there are symptoms of illness but no clear measures by which to make a diagnosis. In the past, functional disorders were largely considered psychosomatic. Today, we recognize that many of these conditions have distinctive characteristics that define them irrespective of a person's emotional state.

Pruritus (itching) is one such example of a functional symptom. On its own, it is associated with neither a physical or biochemical change but remains a very real and tangible sensation. The same applies to fatigue, chronic headaches, or insomnia. The absence of measurable biomarkers doesn't mean that they don't exist; it simply tells us that the causes are unknown (idiopathic).

In years past, diseases like epilepsy, migraine, and Alzheimer's were once considered functional disorders. Today, that is no longer the case.

Many functional disorders are today being classified by their symptomatic profile. Examples include:

  • Irritable bowel syndrome (IBS)
  • Chronic fatigue syndrome (CFS)
  • Fibromyalgia
  • Temporomandibular joint pain (TMJ)
  • Gastroesophageal reflux disorder (GERD)
  • Interstitial cystitis

Functional vs. Psychosomatic Symptoms

Psychiatric illnesses are also largely considered functional since we cannot readily identify their underlying cause. These include clinical depression, bipolar disorder, schizophrenia, attention deficit hyperactivity disorder (ADHD), obsessive-compulsive disorder (OCD), and post-traumatic stress syndrome (PTSD).

However, a psychiatric illness is not the same thing as a psychosomatic one. Psychosomatic symptoms are those that are believed derived from the stresses and strains of everyday living. They are driven by a person's mental or emotional state and often manifest with symptoms of a backache, headache, fatigue, high blood pressure, indigestion, shortness of breath, dizziness, and impotence.

Functional symptoms differ from psychosomatic ones in that the removal of the emotional stress may lessen the severity of symptoms but not entirely erase them.

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  • Grover, M.; Herfarth, H.; and Drossman, D. "The Functional–Organic Dichotomy: Postinfectious Irritable Bowel Syndrome and Inflammatory Bowel Disease–Irritable Bowel Syndrome." Clin Gastro Hepato. 2008: 7(1):48–53. doi:10.1016/j.cgh.2008.08.032.

  • Wise, T. "Update on consultation-liaison psychiatry (psychosomatic medicine)". Curr Opin Psychiatry. 2008; 21(2):96-200. doi:10.1097/YcO.0bo132328f3393ae.

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.