Start by allowing Ovid to map your keyword phrase to MeSH.
Using the Medical Subject Headings (MeSH) is efficient because they search for matching content rather than text. Ovid's mapping is designed to suggest MeSH for your concept. Simply type in a word or phrase into Ovid's Advanced Search and make sure that Map Term to Subject Heading is enabled. Here's a repetitive example of how that happens:
Ovid displays as blue links the MeSH that are associated with your keywords in a list of descending frequency. The terms you entered into your search appear at the bottom of results. Check the box to its left if you want to include your keyword (phrase) with or without the MeSH you select.
This table shows subheadings that can be attached to a MeSH in the Diseases Tree (or hierarchy of MeSH). Other trees invoke different tables of subheadings. Ovid will combine your selection with OR (unless you switch to AND). If your concept does not match any subheadings, check All or simply hit return to ignore the particular options.
Groups of subheadings are commonly employed for comprehensively specifying a broad concept like diagnosis: