Alopecia Areata Medicaid Improvement and Parity Act of 2008 - Amends title XIX (Medicaid) of the Social Security Act with respect to inpatient hospital services to require states to provide hair prostheses under the Medicaid program for: (1) individuals diagnosed with alopecia areata universalis or alopecia areata totalis; or (2) individuals whose attending physician certifies in writing the medical necessity of that proposed course of rehabilitative treatment.