patchy alopecia Biblioteca Nacional de Medicina de Estados Unidos bald spot Encyclopedia: Alopecia Areata alopecia medlineplus.gov Alopecia areata medlineplus.gov/ency/article/001450.htm doctor may recommend bald spot https://medlineplus.gov/ency/article/001450.htm medlineplus.gov/ency/article/001450.htm bald spot bald spot https://medlineplus.gov/ency/article/001450.htm medlineplus.gov/ency/article/001450.htm