Table of ContentsView AllTable of ContentsDifferencesOrganic DiseasesFunctional DiseasesDebate
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Table of Contents
Differences
Organic Diseases
Functional Diseases
Debate
A disease can sometimes be described as being organic or functional. By the broadest definition:
The key difference between an organic and functional disease is that the cause and pathophysiology (disease pathway) of an organic disease have largely been established, while the cause and pathophysiology of a functional disease have largely not.
Many diseases fall under the umbrella of being either organic or functional. The terms may not only be applied to physiological conditions (related to the body) but also tomental healthconditions.
This article explains the difference between organic and functional diseases and why the distinction is important in medical practice.
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Distinguishing Between an Organic and Functional Disease
For instance, persistent tiredness may be due to an organic cause likeanemia, which can be definitively diagnosed with ared blood cell (RBC) count. Or, it could be due to a functional cause likechronic fatigue syndromefor which no measurable test is available.
This is not to suggest that the lack of testing means that a functional disease is “less real” than an organic disease. As the scientific understanding of a disease advances, the way in which that disease is categorized can change.
Epilepsyis one such example. While the seizure disorder was once considered functional, it is now regarded as an organic neurological condition.
Determining whether the cause is organic or functional is central to delivering the appropriate treatment. It is not always a straightforward process.
Organic diseases describe a broad category of conditions in which tissues or organs are affected, leading to symptoms and illness. These include infectious diseases, inflammatory diseases, metabolic disorders, neurological diseases, autoimmune disorders, and cancer.
With an organic disease, there will be tests and procedures that can detect or measure biological and/or anatomical changes that lead to illness or dysfunction. These may involve blood tests, imaging studies, medical instruments, or surgical procedures.
Examples include:
This is not to suggest that all organic diseases can be diagnosed in a straightforward and definitive manner. Some require multiple tests to support the diagnosis when a single test is unable to do so.
One example isceliac disease (CD). In addition to antibody tests, a small bowel biopsy, and agluten-free diet, genetics tests called HLA-DQ2 and HLA-DQ8 may be used to see if you have a genetic predisposition for CD. While the tests are not diagnostic of CD (you can have these mutations and not have CD), the absence of mutations is uncommon in CD.
Other organic diseases may also require complicated testing to not only evidence the disease but also rule out other possible causes–including functional ones.
Broadly speaking, a functional disease is one in which there is no diagnosable pathophysiology to account for your symptoms.It is unclear where the problem is originating and how exactly it causes symptoms.
A functional disease may occur when an organ doesn’t function as it should or there is some sort of miscommunication between systems (such as the brain and the gut). The symptoms are generally persistent and cause significant impairment or disability. While the symptoms may be disruptive, they are generally not life-threatening.
The term “functional disorder” is generally taken to mean a functional somatic disorder (meaning one involving the body). The term can also be applied to many, but not all, psychiatric illnesses.
Functional Somatic Disorders
There are many conditions classified as functional somatic disorders (FSDs). These can cause symptoms limited to certain organs or affect the body as a whole.
Functional somatic disorders should not be confused withsomatic symptom disorder (SSD). SSD is a condition in which persistent physical symptoms are due to psychological problems.
Examples of conditions classified as FSDs include:
It is not uncommon for some of these disorders to overlap. Fibromyalgia and ME/CFS frequently co-occur, suggesting that the two disorders have similar disease origins or pathways.
Debating Psychiatric Illness as a Functional Condition
While psychiatric illnesses meet the strict definition of a functional disorder, there is considerable debate as to whether the term is appropriate in this setting.
However, many mental health experts argue that classifying them as “functional” suggests that the causes are inherently unknown and the conditions “appear out of nowhere.”
Certainly, with conditions like depression and PTSD, scientists recognize that environmental, social, emotional, and neurological factors contribute to the onset of these conditions. Moreover, the drugs used to treat depression andattention-deficit hyperactivity disorder (ADHD)have specific neuropsychiatric effects that are no more or less consistent than with any other drug.
Even with respect to functional disorders, experts question whether they should be strictly classified as “somatic” and “mental” given that FSD and SSD frequently overlap. In 2020, experts in Europe recommended that “functional somatic disorders” neither be classified as purely somatic nor purely mental, but ones that occupy a neutral space in between.
Summary
Strictly speaking, an organic disease is one in which there are measurable biological changes in tissues and organs that lead to symptoms. Examples include infections, autoimmune diseases, and cancer.
A functional disease is one in which there are symptoms but with no measurable changes in tissues. Examples include fibromyalgia, chronic fatigue syndrome, and irritable bowel syndrome.
With an organic disease, the cause and disease pathway have largely been established, while the cause and disease pathway of a functional disease is often less understood.
13 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Bell V, Wilkinson S, Greco M, Hendrie C, Mills B, Deeley Q.What is the functional/organic distinction actually doing in psychiatry and neurology?Wellcome Open Res.2020;5:138. doi:10.12688/wellcomeopenres.16022.1Maffei ME.Fibromyalgia: recent advances in diagnosis, classification, pharmacotherapy and alternative remedies.Int J Mol Sci. 2020 Oct 23;21(21):7877. doi:10.3390/ijms21217877.Shaukat A, Kahi CJ, Burke CA, et al.ACG clinical guidelines: colorectal cancer screening 2021.Am J Gastroenterol. 2021 Mar 1;116(3):458-479. doi:10.14309/ajg.0000000000001122U.S. Preventive Services Task Force, Owens DK, Davidson KW, Krist AH, et. al.Screening for HIV infection: US Preventive Services Task Force recommendation statement.JAMA. 2019 Jun 18;321(23):2326-2336. doi:10.1001/jama.2019.6587National Heart, Lung, and Blood Institute.High blood pressure diagnosis.Compston JE, Mcclung MR, Leslie WD.Osteoporosis.Lancet. 2019;393(10169):364-376. doi:10.1016/S0140-6736(18)32112-3National Institute of Diabetes and Digestive and Kidney Diseases.Diagnosis of peptic ulcers (stomach ulcers).American Diabetes Association Professional Practice Committee.2. Diagnosis and classification of diabetes:Standards of Care in Diabetes-2024.Diabetes Care. 2024;47(Suppl 1):S20-S42. doi:10.2337/dc24-S002Zhu J, Mulder CJ, Dieleman LA.Celiac disease: against the grain in gastroenterology.J Canadian Assoc Gastroenterol.2018. doi:10.1093/jcag/gwy042Burton C, Fink P, Henningsen P, Löwe B, Rief W.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Medicine.2020;18(1):34. doi:10.1186/s12916-020-1505-4Natelson BH.Myalgic encephalomyelitis/chronic fatigue syndrome and fibromyalgia: definitions, similarities, and differences.Clin Ther. 2019;41(4):612-618. doi:10.1016/j.clinthera.2018.12.016Thoma M, Froehlich L, Hattesohl DBR, Quante S, Jason LA, Scheibenbogen C.Why the Psychosomatic View on Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Is Inconsistent with Current Evidence and Harmful to Patients. Medicina (Kaunas). 2023 Dec 31;60(1):83. doi: 10.3390/medicina60010083Burton C, Fink P, Henningsen P, Lowe B, Rief W, EURONET-SOMA Group.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Med.2020;18:34. doi:10.1186/s12916-020-1505-4
13 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Bell V, Wilkinson S, Greco M, Hendrie C, Mills B, Deeley Q.What is the functional/organic distinction actually doing in psychiatry and neurology?Wellcome Open Res.2020;5:138. doi:10.12688/wellcomeopenres.16022.1Maffei ME.Fibromyalgia: recent advances in diagnosis, classification, pharmacotherapy and alternative remedies.Int J Mol Sci. 2020 Oct 23;21(21):7877. doi:10.3390/ijms21217877.Shaukat A, Kahi CJ, Burke CA, et al.ACG clinical guidelines: colorectal cancer screening 2021.Am J Gastroenterol. 2021 Mar 1;116(3):458-479. doi:10.14309/ajg.0000000000001122U.S. Preventive Services Task Force, Owens DK, Davidson KW, Krist AH, et. al.Screening for HIV infection: US Preventive Services Task Force recommendation statement.JAMA. 2019 Jun 18;321(23):2326-2336. doi:10.1001/jama.2019.6587National Heart, Lung, and Blood Institute.High blood pressure diagnosis.Compston JE, Mcclung MR, Leslie WD.Osteoporosis.Lancet. 2019;393(10169):364-376. doi:10.1016/S0140-6736(18)32112-3National Institute of Diabetes and Digestive and Kidney Diseases.Diagnosis of peptic ulcers (stomach ulcers).American Diabetes Association Professional Practice Committee.2. Diagnosis and classification of diabetes:Standards of Care in Diabetes-2024.Diabetes Care. 2024;47(Suppl 1):S20-S42. doi:10.2337/dc24-S002Zhu J, Mulder CJ, Dieleman LA.Celiac disease: against the grain in gastroenterology.J Canadian Assoc Gastroenterol.2018. doi:10.1093/jcag/gwy042Burton C, Fink P, Henningsen P, Löwe B, Rief W.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Medicine.2020;18(1):34. doi:10.1186/s12916-020-1505-4Natelson BH.Myalgic encephalomyelitis/chronic fatigue syndrome and fibromyalgia: definitions, similarities, and differences.Clin Ther. 2019;41(4):612-618. doi:10.1016/j.clinthera.2018.12.016Thoma M, Froehlich L, Hattesohl DBR, Quante S, Jason LA, Scheibenbogen C.Why the Psychosomatic View on Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Is Inconsistent with Current Evidence and Harmful to Patients. Medicina (Kaunas). 2023 Dec 31;60(1):83. doi: 10.3390/medicina60010083Burton C, Fink P, Henningsen P, Lowe B, Rief W, EURONET-SOMA Group.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Med.2020;18:34. doi:10.1186/s12916-020-1505-4
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
Bell V, Wilkinson S, Greco M, Hendrie C, Mills B, Deeley Q.What is the functional/organic distinction actually doing in psychiatry and neurology?Wellcome Open Res.2020;5:138. doi:10.12688/wellcomeopenres.16022.1Maffei ME.Fibromyalgia: recent advances in diagnosis, classification, pharmacotherapy and alternative remedies.Int J Mol Sci. 2020 Oct 23;21(21):7877. doi:10.3390/ijms21217877.Shaukat A, Kahi CJ, Burke CA, et al.ACG clinical guidelines: colorectal cancer screening 2021.Am J Gastroenterol. 2021 Mar 1;116(3):458-479. doi:10.14309/ajg.0000000000001122U.S. Preventive Services Task Force, Owens DK, Davidson KW, Krist AH, et. al.Screening for HIV infection: US Preventive Services Task Force recommendation statement.JAMA. 2019 Jun 18;321(23):2326-2336. doi:10.1001/jama.2019.6587National Heart, Lung, and Blood Institute.High blood pressure diagnosis.Compston JE, Mcclung MR, Leslie WD.Osteoporosis.Lancet. 2019;393(10169):364-376. doi:10.1016/S0140-6736(18)32112-3National Institute of Diabetes and Digestive and Kidney Diseases.Diagnosis of peptic ulcers (stomach ulcers).American Diabetes Association Professional Practice Committee.2. Diagnosis and classification of diabetes:Standards of Care in Diabetes-2024.Diabetes Care. 2024;47(Suppl 1):S20-S42. doi:10.2337/dc24-S002Zhu J, Mulder CJ, Dieleman LA.Celiac disease: against the grain in gastroenterology.J Canadian Assoc Gastroenterol.2018. doi:10.1093/jcag/gwy042Burton C, Fink P, Henningsen P, Löwe B, Rief W.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Medicine.2020;18(1):34. doi:10.1186/s12916-020-1505-4Natelson BH.Myalgic encephalomyelitis/chronic fatigue syndrome and fibromyalgia: definitions, similarities, and differences.Clin Ther. 2019;41(4):612-618. doi:10.1016/j.clinthera.2018.12.016Thoma M, Froehlich L, Hattesohl DBR, Quante S, Jason LA, Scheibenbogen C.Why the Psychosomatic View on Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Is Inconsistent with Current Evidence and Harmful to Patients. Medicina (Kaunas). 2023 Dec 31;60(1):83. doi: 10.3390/medicina60010083Burton C, Fink P, Henningsen P, Lowe B, Rief W, EURONET-SOMA Group.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Med.2020;18:34. doi:10.1186/s12916-020-1505-4
Bell V, Wilkinson S, Greco M, Hendrie C, Mills B, Deeley Q.What is the functional/organic distinction actually doing in psychiatry and neurology?Wellcome Open Res.2020;5:138. doi:10.12688/wellcomeopenres.16022.1
Maffei ME.Fibromyalgia: recent advances in diagnosis, classification, pharmacotherapy and alternative remedies.Int J Mol Sci. 2020 Oct 23;21(21):7877. doi:10.3390/ijms21217877.
Shaukat A, Kahi CJ, Burke CA, et al.ACG clinical guidelines: colorectal cancer screening 2021.Am J Gastroenterol. 2021 Mar 1;116(3):458-479. doi:10.14309/ajg.0000000000001122
U.S. Preventive Services Task Force, Owens DK, Davidson KW, Krist AH, et. al.Screening for HIV infection: US Preventive Services Task Force recommendation statement.JAMA. 2019 Jun 18;321(23):2326-2336. doi:10.1001/jama.2019.6587
National Heart, Lung, and Blood Institute.High blood pressure diagnosis.
Compston JE, Mcclung MR, Leslie WD.Osteoporosis.Lancet. 2019;393(10169):364-376. doi:10.1016/S0140-6736(18)32112-3
National Institute of Diabetes and Digestive and Kidney Diseases.Diagnosis of peptic ulcers (stomach ulcers).
American Diabetes Association Professional Practice Committee.2. Diagnosis and classification of diabetes:Standards of Care in Diabetes-2024.Diabetes Care. 2024;47(Suppl 1):S20-S42. doi:10.2337/dc24-S002
Zhu J, Mulder CJ, Dieleman LA.Celiac disease: against the grain in gastroenterology.J Canadian Assoc Gastroenterol.2018. doi:10.1093/jcag/gwy042
Burton C, Fink P, Henningsen P, Löwe B, Rief W.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Medicine.2020;18(1):34. doi:10.1186/s12916-020-1505-4
Natelson BH.Myalgic encephalomyelitis/chronic fatigue syndrome and fibromyalgia: definitions, similarities, and differences.Clin Ther. 2019;41(4):612-618. doi:10.1016/j.clinthera.2018.12.016
Thoma M, Froehlich L, Hattesohl DBR, Quante S, Jason LA, Scheibenbogen C.Why the Psychosomatic View on Myalgic Encephalomyelitis/Chronic Fatigue Syndrome Is Inconsistent with Current Evidence and Harmful to Patients. Medicina (Kaunas). 2023 Dec 31;60(1):83. doi: 10.3390/medicina60010083
Burton C, Fink P, Henningsen P, Lowe B, Rief W, EURONET-SOMA Group.Functional somatic disorders: discussion paper for a new common classification for research and clinical use.BMC Med.2020;18:34. doi:10.1186/s12916-020-1505-4
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