Get Nosology essential facts below. View Videos or join the Nosology discussion. Add Nosology to your PopFlock.com topic list for future reference or share this resource on social media.
Branch of medicine that deals with classification of diseases
Nosology (from Ancient Greek (nosos) 'disease', and - (-logia) 'study of-') is the branch of medical science that deals with the classification of diseases. Fully classifying a medical condition requires knowing its cause (and that there is only one cause), the effects it has on the body, the symptoms that are produced, and other factors. For example, influenza is classified as an infectious disease because it is caused by a virus, and it is classified as a respiratory infection because the virus infects and damages certain tissues in the respiratory tract. The more that is known about the disease, the more ways the disease can be classified nosologically.
Nosography is a description whose primary purpose is enabling a diagnostic label to be put on the situation. As such, a nosographical entity need not have a single cause. For example, inability to speak due to advanced dementia and an inability to speak due to a stroke could be nosologically different but nosographically the same.
Alternatively, diseases may be classified according to the organ system involved, though this is often complicated since many diseases affect more than one organ.
A chief difficulty in nosology is that diseases often cannot be defined and classified clearly, especially when cause or pathogenesis are unknown. Thus diagnostic terms often only reflect a symptom or set of symptoms (syndrome).
Traditionally diseases were defined as syndromes by their symptoms. When more information is available, they are also defined by the damage they produce. When cause is known, they are better defined by their cause, though still important are their characteristics.
Probably the last described kind of diseases are molecular diseases, defined by their molecular characteristics. This was introduced in November 1949, with the seminal paper, "Sickle Cell Anemia, a Molecular Disease", in Science magazine, Linus Pauling, Harvey Itano and their collaborators laid the groundwork for establishing the field of molecular medicine.
Several classifications of diseases have been historically proposed, and normally all of them assign a code to every supported disease. Some of them codify diseases following the path of the classification tree, and others like SNOMED use a multifactor classification system.
There are also coding systems for symptoms present in the diseases and biological findings. They are normally included in medical dictionaries, also with a codification system. Some of them are MeSH (Medical Subject Headings), COSTART (Coding Symbols for Thesaurus of Adverse Reaction Terms) or MedDRA (Medical Dictionary for Regulatory Activities) Other systems like Current Procedural Terminology do not deal directly with diseases but with the related procedures.
The term disease broadly refers to any condition that impairs the normal functioning of the body. For this reason, diseases are associated with dysfunctioning of the body's normal homeostatic process. Commonly, the term disease is used to refer specifically to infectious diseases, which are clinically evident diseases that result from the presence of pathogenic microbial agents, including viruses, bacteria, fungi, protozoa, multicellular organisms, and aberrant proteins known as prions. An infection that does not and will not produce clinically evident impairment of normal functioning, such as the presence of the normal bacteria and yeasts in the gut, or of a passenger virus, is not considered a disease. By contrast, an infection that is asymptomatic during its incubation period, but expected to produce symptoms later, is usually considered a disease. Non-infectious diseases are all other diseases, including most forms of cancer, heart disease, and genetic disease.
Illness and sickness are generally used as synonyms for disease. However, these terms are occasionally used to refer specifically to the patient's personal experience of his or her disease. In this model, it is possible for a person to have a disease without being ill (to have an objectively definable, but asymptomatic, medical condition), and to be ill without being diseased (such as when a person perceives a normal experience as a medical condition, or medicalizes a non-disease situation in his or her life).
A syndrome is the association of several medical signs, symptoms, and or other characteristics that often occur together. Some syndromes, such as Down syndrome, have only one cause; others, such as Parkinsonian syndrome, have multiple possible causes. In other cases, the cause of the syndrome is unknown. A familiar syndrome name often remains in use even after an underlying cause has been found, or when there are a number of different possible primary causes.
In cases of viral infections, like HIV, it is important to make a difference between the infection (considered as a disease, even while it is silent) and the associated symptoms (a syndrome). In the case of HIV the syndrome is named AIDS.
Injury and lesions
Injury is damage to the body. This may be caused by accidents, falls, hits, weapons, and other causes. Major trauma is injury that has the potential to cause prolonged disability or death. Lesion is any abnormality in the tissue of an organism (in layman's terms, "damage"), usually caused by disease or trauma. Lesion is derived from the Latin word laesio meaning injury. Similar to the ICD-10 the World Health Organization produces the International Classification of External Causes of Injury (ICECI). Sequelae of resolved diseases sometimes are considered inside lesions and other times inside diseases.
Some medical conditions cannot be classified in any of these groups, but they can still be important enough to be considered as medical conditions. For example, to be a carrier of a genetical disease, or a viral infection unable to progress to disease, normally is not considered inside any of the previous groups. Cases of infections able to progress, but with low possibilities, like latent tuberculosis, are also considered outside the category of diseases.
The term "medical condition" can also be applied to physiological states outside the context of disease, as for example when referring to "symptoms of pregnancy". It can also refer to the normal residual scars of a disease after it has resolved, for example lung fibrosis after a tuberculosis.
Ancient medical treatises had a variety of different ways of classifying and grouping illnesses. Chinese texts like the Huangdi Neijing categorized diseases by which of the atmospheric influences was believed to be responsible for them. Many ancient Greek, Mesopotamian, Roman, and Egyptian authors categorized diseases by the body parts they affected, while others divided diseases into acute or chronic illnesses. Mental disorders were classified into categories like mania and paranoia by Hippocrates, and this system was utilized by later authors like Najib ad-Din Samarqandi.
Many popular ancient disease classification systems largely relied upon humorism, which carried over into medieval times. Early attempts to develop more comprehensive approaches to the classification of diseases were made by Jean Fernel in the 16th century. Early modern nosological efforts grouped diseases by their symptoms, whereas modern systems focus on grouping diseases by the anatomy and cause involved.
In the 17th century, the English physician Thomas Sydenham was the first to propose a syndrome-based classification of diseases. For Sydenham a disease and a syndrome were equivalent concepts.
^Murthy, R. Srinivasa; Wig, Narendra N. (22 April 2002). "Psychiatric Diagnosis and Classification in Developing Countries". In Mario Maj (ed.). Psychiatric Diagnosis and Classification. Wiley. ISBN978-0471496816.