Yes this is possible, but for many payers (including Medicare) only in the outpatient setting, and only if the circumstances were such that both problems could not have been adressed in a single office encounter. So if the problem evaluated second had not yet occurred by the time of the earlier appointment, this would be ok.
This is one of the RARE occasions where two E/Ms can be billed in the same day by the same provider.
Per the November 2004 CPT Assistant regarding the language in Modifier 25's description that mentions that it is used to bill an E/M on the same day as either a procedure or an "other service":
Typically, “other service” is understood to mean an E/M service that would ordinarily include the separately identifiable E/M service on the same day. Or, the “other service” could be one of two separately identifiable E/M services provided on the same day...
Here's Medicare's wording found on p. 47 of Chapter 12 of their Claims Processing Manual at this link: http://www.cms.gov/manuals/downloads/clm104c12.pdf
B Office/Outpatient E/M Visits Provided on Same Day for Unrelated Problems
As for all other E/M services except where specifically noted, carriers may not pay two E/M office visits billed by a physician (or physician of the same specialty from the same group practice) for the same beneficiary on the same day unless the physician documents that the visits were for unrelated problems in the office or outpatient setting which could not be provided during the same encounter (e.g., office visit for blood pressure medication evaluation, followed five hours later by a visit for evaluation of leg pain following an accident).
Even payers that allow this rare occurrence will often deny the claim initially, but should pay on appeal.