Senior Citizen Protection Act of 1998 - Amends title XIX (Medicaid) of the Social Security Act to extend the authority of State Medicaid fraud control units, upon the approval of the Inspector General of the relevant Federal agency, to investigate and prosecute: (1) fraud in connection with other Federal health care programs (if the suspected fraud or law violation is primarily related to the State Medicaid plan); and (2) at a unit's option, abuse of residents of non-Medicaid board and care facilities.

Provides that overpayments collected by a State Medicaid fraud control unit shall be credited to, and be available for expenditure under, the Federal health care program that was subject to the activity that was the basis for the collection.