Antibodies to a brain‐type creatine kinase associated with paraneoplastic neurological syndromes

Background Previously, we identified a brain‐type creatine kinase antibody to be associated with paraneoplastic cerebellar degeneration using a proteomic approach. Immunohistochemistry showed that this antibody reacted with both mouse cerebellar neurons and bladder cancer tissues. Furthermore, we detected this antibody in sera from two paraneoplastic cerebellar degeneration patients with small cell lung cancer and one lymphoma patient. In total, we detected four paraneoplastic cerebellar degeneration patients. Aim To confirm the new onconeural antibody, we investigated whether this autoantigen is expressed in both human cerebellum and cancer tissues (small cell lung cancer of lymphoma). Methods We examined sera from two paraneoplastic cerebellar degeneration patients with small cell lung cancer, one lymphoma patient and a patient with sensory‐motor neuropathy as paraneoplastic neurological syndrome by western blotting and enzyme‐linked immunosorbent assay to explore creatine kinase brain‐type antibody expressions in these cancer cells as well as in the human cerebellum. Sera from the patients without paraneoplastic cerebellar degeneration were used as controls. In addition, we examined the serum from a patient with sensory‐motor neuropathy as paraneoplastic neurological syndrome by western blot. Results The mean serum values of creatine kinase brain‐type antibodies in paraneoplastic cerebellar degeneration patients with small cell lung cancer were significantly higher than those of small cell lung cancer patients without paraneoplastic cerebellar degeneration. Immunohistochemistry detected this autoantigen expression in both abovementioned specimens. We also detected this antibody in the serum in sensory‐motor neuropathy as paraneoplastic neurological syndrome. Conclusion Our study showed that this antibody was produced in four paraneoplastic cerebellar degeneration patients, and that this autoantigen expression was evident in human cerebellum and cancer. These findings show that creatine kinase brain‐type antibody might be a novel antibody associated with paraneoplastic neurological syndrome.