Paraneoplastic syndromes are diagnosed primarily on the basis of clinical symptoms, response to treatment, and the combination of specific antibodies. Firstly, if the patient presents with more typical paraneoplastic syndromes, such as limbic encephalitis, encephalomyelitis, Lambert-Eaton syndrome, etc., and a tumor develops within five years of diagnosis, the diagnosis of paraneoplastic syndromes can be confirmed. Secondly, if the manifestations of paraneoplastic syndrome are not typical, but specific antibodies related to paraneoplastic syndrome such as Hu antibody, Yo antibody and Ri antibody can be detected, then paraneoplastic syndrome may be considered in conjunction with the clinical picture. If the patient’s clinical manifestations are not typical of paraneoplastic syndromes such as Lambert-Eaton syndrome and limbic encephalitis, but the patient’s clinical symptoms improve with immunotherapy, it may be the basis for the diagnosis of paraneoplastic syndromes.