Nosology deals with the concept, definition, classification, and nomenclature of disease.

The Nosology of Disease, 1666

Nosology is the branch of medicine that deals with the concept, definition, classification, and nomenclature of disease.

Thomas Sydenham

The historic development of nosology was fundamental to the evolution of diagnosis. A concept essential to modern medicine is that a particular disease can cause manifestations that can be quite different from one individual to another. The definition of what constitutes a disease began with Thomas Sydenham in seventeenth-century England. Sydenham (1624–1689) was born at Wynford Eagle in Dorset. He obtained his bachelor of medicine from Oxford in 1648. He was a captain in the cavalry during Oliver Cromwell’s campaign in Scotland against Charles II. When the Restoration came in 1660 and Charles II became king, Sydenham had no political future “and he had no resource other than a serious devotion to the practice of medicine, an event with important benefits to all succeeding generations of physicians” (Harvey, 1973). He began practicing medicine in London in 1663, after having a lot of trouble passing the examination of the Royal College of Physicians.

The London of Sydenham’s day was notable for the occurrence of one murderous epidemic after another. An epidemic of an acute infectious disease such as smallpox or cholera, which struck thousands suddenly and left just as swiftly, provided the ideal setting for the development of modern nosologic concepts: a great many previously healthy individuals were suddenly afflicted by what was clearly the same illness, which at the same time varied in its manifestations from one person to another. An idea of the magnitude of these epidemics can be gotten from population estimates: in 1665 the plague killed about 100,000 of 600,000 inhabitants. The plague stopped by 1667, but in that year smallpox killed 1300, cholera 2000, phthisis 3000, and only 1000 died of old age. These figures, although of questionable exactness, nevertheless depict accurately the effects of these diseases.

In contrast to his contemporaries, Sydenham thought it was possible, albeit difficult, to construct an accurate picture of each disease:

And, in truth, it is my opinion that the principal reason of our yet being destitute of an accurate history of diseases, proceeds from a general supposition that diseases are no more than the confused and irregular operations of disordered and debilitated nature, and consequently that it is a fruitless labor to endeavor to give a just description of them.

… The symptoms observed by Socrates in his illness may generally be applied to any other person afflicted with the same disease, in the same manner as the general marks of plants justly run through the same plants of every kind. Thus, for instance, whoever describes a violet exactly as to its colour, taste, smell, form, and other properties, will find the description agrees in most particulars, with all the violets in the universe.

Sydenham laid down four principles that he felt to be important :

  1. All diseases should be classified in species, just as botanists do plants.
  2. Hypotheses and philosophical speculations should be eschewed in favor of an objective description of each disease, described with the same accuracy as when an artist paints a portrait.
  3. The manifestations that are constant in each patient with a particular disease should be distinguished from other phenomena that could be due to the age, constitution, or treatment of the patient.
  4. The season of the year in which the disease occurs should be noted because some diseases “follow the season as surely as many birds and plants.”

Sydenham’s first book was on fever: Methodus Curandi Febres 1666. His most prominent work is Tractatus de Podagra et Hydrope 1683. In it he separated gout (from which he suffered) from the entities that had been called rheumatism. Sydenham stressed personal independent observation. He “first gave clinical observation its place of honor as a scientific method—one which for those who cultivate it effectively is still today a basic asset of the complete physician” .


The next physician interested in the classification of diseases was Sauvages. In 1731 he published a book in which he grouped diseases in classes, orders, and genera, just as the biologists were doing with plants and animals. This book came to the attention of Linnaeus, who published his Systema Naturae in 1735. The two men carried on a lifelong correspondence. Sauvages published his principal work in 1763, Nosologia methodica sistens moborum classes, genera et species. He described 2400 diseases, divided into 10 classes and 40 orders. In the preface he discussed principles for classifying disease, choosing symptoms as the basis for his scheme. This led to many difficulties, given the nature of medical knowledge at the time. There were 18 kinds of angina, 19 types of asthma, 19 species of dysphagia, 13 different species of anorexia, etc. This work had much influence upon contemporary medicine; detailed nosologies following his system appeared in various countries. These nosologies, however, did not appreciably influence the practice of medicine. The differences between the nosologists of the eighteenth century and Sydenham is that they merely catalogued and arranged symptoms, while he characterized diseases. Sydenham delineated each disease by its manifestations and clinical course. Succeeding nosologists classified symptoms. The distinction between symptom and disease was not appreciated.


He characterized 2700 diseases and divided them into classes, orders, genera, and species

The next advance was the development of the discipline of pathologic anatomy by Morgagni, which is described below. Morgagni established the concept of whole organs being diseased. Philippe Pinel of Paris published his Nosologie philosophique in 1798. This book stressed the importance of arriving at the typical picture of a disease, ignoring the varying picture in each individual patient. He characterized 2700 diseases and divided them into classes, orders, genera, and species. He grouped diseases that involved a particular tissue together, such as all diseases of the mucous membranes. This was an entirely new concept. Previous authors had arranged disorders according to anatomic location: heart, lungs, etc. Bichat expanded upon this idea and showed how disease of each type of tissue could give rise to two different kinds of symptoms. One group of symptoms is dependent upon the particular tissue involved, and the other group is caused by dysfunction of the affected organ. Laennec, who was greatly influenced by Bichat, produced a revolution in nosography with the publication of his book on auscultation (see below). Laennec wove symptoms, signs, and pathologic findings into a series of classic diseases, many of which he was the first to describe: emphysema, bronchiectasis, pneumothorax. His great achievement was to take many different conditions grouped under the name phthisis and show that they were all different stages of one disease, tuberculosis. He “demonstrated that the process usually begins in the apex of the lung, and that various anatomical changes may be demonstrated by means of stethoscopy, and finally he conceived and described tuberculosis of the lungs as a special disease differing from all other disease processes” . Modern nosology begins with Laennec.

Source: Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition.

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