his article highlights the additions and changes in 2004 Medical Subject Headings (MeSH).

Overview of Vocabulary Development and Changes for 2004 MeSH

• 666   descriptors were added representing topics with no directly corresponding descriptors in 2003 MeSH
• 109   descriptors were replaced with more up-to-date terminology
• 20     descriptors were deleted
• 484   see references (entry terms) were added

Case Reports
For 2004, this MeSH heading has been deleted and replaced by a Publication Type, a special kind of descriptor that characterizes the nature of the publication rather than what it is about. The practical meaning of the term has not been altered. The change was made to better reflect the character of the descriptor as used in MEDLINE and MeSH and to place it in context among other Publication Types.

[Update: This section was added on November 25, 2003.]
New Definition for Toxicity Subheading
The definition for the subheading /toxicity has been revised for 2004 to allow the use for both experimental and environmental exposure. Past indexing policy limited the use of the /toxicity subheading to experimental studies that investigated whether a chemical caused harmful effects. This subheading was also allowed to be used for experimental studies of exposure to environmental agents and chemicals. Non-experimental studies of the harmful effects of these environmental agents and chemicals have been indexed with the /adverse effects subheading. This practice was not quite logical as /adverse effects is defined as "Used with drugs, chemicals, or biological agents in accepted dosage - or with physical agents or manufactured products in normal usage." Environmental pollutants do not have accepted dosages or normal usage.

Thus, the /toxicity subheading definition has been adjusted to:

Used with drugs and chemicals for experimental human and animal studies of their ill effects. It includes studies to determine the margin of safety or the reactions accompanying administration at various dose levels. It is used also for exposure to environmental agents. Poisoning should be considered for life-threatening exposure to environmental agents.

Expansion of Trees
The MeSH Trees were expanded from nine to eleven levels to allow a more accurate reflection of the hierarchy in elaborated and complex areas.

Organisms—Category B:
Animals:  the expansion of the MeSH tree structure has allowed for a long-awaited revision concerning the heading ANIMALS, the check tag ANIMAL, and related headings. The old descriptor ANIMALS will be changed to ANIMAL POPULATION GROUPS. It will retain all indented terms. The check tag ANIMAL will be changed to a new descriptor ANIMALS. It will function as both a descriptor and a check tag and will be treed at B1. The singular word Animal will map to this new plural heading.

The former descriptors B1 INVERTEBRATES and B2 VERTEBRATES will be treed under ANIMALS. The old B5 ALGAE AND FUNGI will be split into two descriptors. ALGAE will be at the top of B2 and FUNGI will now be at the top of B5. See 2004 MeSH Changes to the Category B Organisms Tree and the Check Tag Animal. NLM Tech Bull. 2003 Sep-Oct;(334):e5.

Bacteria (B3):   This subcategory was expanded with 310 new descriptors. The changes reflect the revisions in taxonomy presented in: Boone DR, Castenholz RW, Garrity GM, editors. Bergey's manual of systematic bacteriology. 2nd ed. Vol. 1, The Archaea and the deeply branching and phototropic bacteria. New York: Springer; c2001.

Substances—Category D:
Amino Acids, Peptides and Proteins (D12): 246 new descriptors were added. Proteins and Enzymes: A total of 65 new enzyme classes have been added to the category of Enzymes. Several new major enzyme categories include: DNA Repair Enzymes, Metalloexopeptidases, Oxidoreductases Acting on CH-CH Group Donors, Proprotein Convertases, and Ubiquitin-Protein Ligase Complexes.

Electron Transport Chain Complex Proteins and Photosynthetic Reaction Center Complex Proteins were added as new descriptors. These two broad categories bring together the protein components that are part of biological respiration and photosynthesis. There are also several new descriptor classes under each heading which represent specific components of these complexes.

Receptors, G-Protein-Coupled was added as new class to the Cell Surface Receptors. There are over 100 descriptors now re-treed in this category. In addition several new specific G-protein-coupled receptor classes have been added. Receptors, Proteinase-Activated has been added for another class of cell surface receptors that are activated by proteolytic action.

Angiogenic Proteins: A new descriptor class has been added for proteins that regulate the proliferation of new blood vessels. Several existing and new descriptor classes are now treed under this heading.

Complex Mixtures (D20) is a new subtree. It contains descriptors for heterogeneous materials such as Manure, Soil, and Venoms.

Chemical Actions and Uses (D27) consists of the MeSH descriptors used for Pharmacological Activity (PA). It has been re-grouped into Pharmacologic Actions (D27.505), which includes Molecular Mechanisms of Action (D27.505.519), Physiological Effects of Drugs (D27.505.696), and Therapeutic Uses (D27.505.954). The other groups are Specialty Uses of Chemicals (D27.720) and Toxic Actions (D27.888).

The MeSH heading, Antibiotics, has a new preferred heading, Anti-Bacterial Agents. Antibiotics remains an entry term. The heading was renamed because the formal meaning of antibiotics is something produced by a living organism that is used to kill other organisms. According to this formal meaning, sulfa drugs, quinolones, and other agents commonly used in this way are not antibiotics. Additionally, semi-synthetic antibiotics that alter what is produced naturally do not fit this description. Anti-Bacterial Agents more aptly describe these substances.

In the D27 subtree, descriptors which included chemical structure in the name were removed. For example, Antibiotics, Aminoglycoside was deleted and those citations maintained to Anti-Bacterial Agents (formerly Antibiotics) and to Aminoglycosides. In addition, Noxae (formerly D5) and Specialty Uses (formerly D26) have been moved to the Chemical Actions and Uses grouping. The duplicated tree of Anti-Infective Agents (formerly D20) has been deleted.

Other revised chemical groups include Xanthones and Flavonoids. Many of the flavones required retreeing to the appropriate area in the restructured flavonoids section.

Physiology—Category G:
Circulatory and Respiratory Physiology (G9) and Musculoskeletal Physiology (G11.427) were restructured into two new categories: physiological phenomena and physiological process, while maintaining the subgroupings of Blood Physiology, Cardiovascular Physiology, Respiratory Physiology, and Musculoskeletal Physiology. This was done by creating eight new headings to make the subgroupings: Blood Physiologic Phenomena, Blood Physiologic Processes, Cardiovascular Physiologic Phenomena, Cardiovascular Physiologic Processes, Respiratory Physiologic Phenomena , Respiratory Physiologic Processes, Musculoskeletal Physiologic Phenomena , and Musculoskeletal Physiologic Processes.

Ethnic Groups and Geographic Origins—Categories I and M:
The MeSH descriptor Racial Stocks,and its four children (Australoid Race, Caucasoid Race, Mongoloid Race, and Negroid Race) have been deleted from MeSH in 2004 along with Blacks and Whites. Race and ethnicity have been used as categories in biomedical research and clinical medicine. Recent genetic research indicates that the degree of genetic heterogeneity within groups and homogeneity across groups make race per se a less compelling predictor.

2003 MeSH Subtree

PubMed
PubMed will use 2004 MeSH in its translation tables and MeSH Database as well as in the citation data as soon as end-of-year activities are completed. Please see the article, MEDLINE^®/PubMed^® End-of-Year Activities. NLM Tech Bull. 2003 Sep-Oct;(334):e7, for more information about these activities.

Additional Information
The following files:

• New Headings with Scope Notes [247KB]
  
• Replaced Headings [12KB]
  
• MN (tree number) Changes [534KB]

may be downloaded from Medical Subject Headings - Files Available to Download. Scroll down to the last three links under the 2004 MeSH category on this page. Clicking on any of these three links takes you to a Memorandum of Understanding. Scroll down to the bottom and click the "I agree with these conditions" button. Next, complete the MeSH Registration Form and click the Submit button at the bottom of the form. Next, verify that your information has been correctly entered and then click on the Proceed button. Scroll down to the last three links under the 2004 MeSH category to download the three files.

For more information about 2004 MeSH, please see the MeSH home page at: http://www.nlm.nih.gov/mesh/meshhome.html.

[Editor's Note added on December 23, 2003:
The MeSH Home page has been updated with the 2004 Introduction to MeSH including the New 2004 Medical Subject Headings, Alphabetic List; Changed Descriptors - 2004; Deleted Descriptors - 2004; and New 2004 MeSH Headings, by Tree Subcategory.

Ordering information for the "Black & White" MeSH is also available. This publication includes an alphabetic list of MeSH headings and the tree structures and is included as part of the January issue of a subscription to Index Medicus, but may also be ordered individually.]

Please note that as of November 17, the default for the MeSH Browser is to the 2004 vocabulary.

[Editor's note added on December 8, 2003: Please see MEDLINE Data Changes - 2004. NLM Tech Bull. 2003 Nov-Dec;(335):e6 for details on MEDLINE data changes.]

Schulman, J. What's New for 2004 MeSH^®. NLM Tech Bull. 2003 Nov-Dec;(335):e3.