Clinical manifestations of vitamin B12 deficiency: the first is skin manifestations, patients may have extensive symmetrical pigmentation, especially in the curved parts of the body, palms, soles, nails and mouth, hair and gray, nails may have pigmentation; vitamin B12 deficiency caused by pernicious anemia can appear white spots and baldness; in the hematological system can have the manifestation of anemia, such as the appearance of anemic face, weakness, In the hematological system, there can be manifestations of anemia, such as anemic face, weakness, enlarged liver and spleen, and in severe cases, skin petechiae and petechiae; in the nervous system, symptoms appear late, with or without anemia, and there can be neurological disorders, demyelination and severe neurological symptoms; in the digestive system, there is vomiting and diarrhea, and in severe cases, there can be fever and enlarged liver and spleen; in the cardiovascular system, because it can cause anemia, there can be anemic heart disease, and heart failure.