I found this link with MSPRC's website and thought it might be helpful to some of you. This link takes you to the PDF lists of all the Medicare diagnosis codes dating back to 2002. http://www.cms.gov/Medicare/Coding/ICD9ProviderDiagnosticCodes/codes.html
You can download the pdf files and open them in Acrobat and then CTRL F search for the codes that show up on your conditional payment letters from Medicare. This will help you sort out medical visits that have been "coded" for payment for non-related medical procedures and visits.
This makes it easier to find and eliminate appointments for pre-existing conditions. You can also scan in a long conditional payment spread sheet, do a conversion to searchable text (OCR) and then use the search feature on that to find the billing codes.
Hope this is helpful to some of you.