| If you use OVID to search Medline, have you noticed it has been stuck on the "December week 4 1999" update for several weeks? Normally, MEDLINE is updated weekly and runs a couple of weeks ahead of the calendar. What is going on? Every year in January, the National Library of Medicine (NLM) updates its Medical Subject Headings (MeSH) to reflect growth and change in medical language. OVID programs the changes, releases a "global update" at the end of January, then resumes our normal weekly updates in February. MeSH is the complex yet powerful heart of Medline. Understanding its controlled vocabulary leads to more accurate and precise searches. How does it work? In everyday usage, a particular condition may have several different names, for example, what one person may call a heart attack someone else might call myocardial infarction. So instead of some articles about this condition being indexed under "heart attacks" and others indexed under "myocardial infarction," the NLM chooses just one term and sticks with it. In this case, the subject heading is Myocardial Infarction. All articles on this topic are assigned this subject heading. Because of this controlled vocabulary, a searcher does not risk missing valuable articles due to the vagaries of natural language. What if you don't know the official MeSH terminology? OVID helps you find the right term for whatever you type in the search box. So if you enter "heart attack," a list of related terms is displayed, starting with "Myocardial Infarction." OVID also provides ways to explore MeSH under the TOOLS icon in its menu bar. Learning and using MeSH are sometimes daunting, but consider the workNLM puts into preparing this controlled vocabulary. For 2000, the National Library of Medicine added 553 new headings and replaced 130 headings. Also, they revised and reorganized headings for all the Nervous System Diseases. Most of these additions reflect the NLM's commitment to staying current. For example, they have added Biomedical Technology, Gatekeeping, Single-Parent Family, Tissue Harvesting and Video-Assisted Surgery. Not only does NLM add new subject headings each year, they also replace some existing headings. For example, Head Injuries is now Craniocerebral Trauma. Sometimes the replaced headings read like a "What's Hot/What's Not" list for the semantically inclined: - Signs of possession are out: Adie's Syndrome becomes Adie Syndrome, Gerstmann's Syndrome becomes Gerstmann Syndrome, Gilbert's Disease becomes . . . well, you get the idea.
- Fans of the letter 's' should not worry however. Although the apostrophe s has fallen to the wayside, plurality is in: Apraxia is out and Apraxias is in. Similarly, Kallikrein is replaced by Kallikreins.
- Some changes are a little overdue: Dataphone is updated to Modem.
- One-word terms have fallen out of favor: Hypersomnia becomes Disorders of Excessive Somnolence and Insomnia becomes Sleep Initiation and Maintenance Disorders. Why say in one word what you can say in four or five?
For those of us who don't know any better, some of the changes just seem arbitrary: Cognitive Symptoms has been changed to Neurobehavioral Manifestations. And some seem downright bizarre: Periodic Disease has been changed to Familial Mediterranean Fever. Then again, some of us just think of it as a heart attack. | 
