Medicare Low-Income Beneficiary Protection Act of 1991 - Amends title XIX (Medicaid) of the Social Security Act to extend Medicaid coverage of Medicare (title XVIII of the Social Security Act) premiums, deductibles, and coinsurance payments to Medicare beneficiaries whose income does not exceed 133 percent of the Federal poverty level beginning in 1993 with respect to payment of deductibles and coinsurance and beginning in 1995 with respect to payment of premiums.