What is Paraneoplastic cerebellar degeneration (PCD)

Paraneoplastic cerebellar degeneration (PCD) is a rare neurological disorder characterized by a widespread loss of Purkinje cells associated with a progressive pancerebellar dysfunction. Paraneoplastic syndromes are a group of rare disorders that are triggered by an abnormal immune system response to an underlying (usually undetected) malignant tumor. Patients with paraneoplastic neurological syndrome (PNS) most often present with neurologic symptoms before an underlying tumor is detected.
Paraneoplastic neurologic syndromes include many neurologic disorders including paraneoplastic cerebellar degeneration (PCD) caused by an immune-mediated mechanism other than a metastatic complication in patients with an underlying malignancy. Any part of the nervous system can be involved depending on the type of primary malignancy.

Paraneoplastic syndromes are a group of rare disorders that include paraneoplastic cerebellar degeneration (PCD). Paraneoplastic syndromes are thought to result from an abnormal immune response to an underlying (and often undetected) malignant tumor. PCD is a rare, non-metastatic complication of cancer. PCD is typically thought to be caused by antibodies generated against tumor cells. Instead of just attacking the cancer cells, the cancer-fighting antibodies also attack normal cells in the cerebellum.[1][2] PCD occurs most often in individuals with the following cancers: ovarian cancer, cancer of the uterus, breast cancer, small-cell lung cancer, and Hodgkin lymphoma. Symptoms of PCD may include dizziness, loss of coordination, blurred vision, nystagmus, ataxia, and speech difficulties.[1]

This information is provided by the National Institutes of Health (NIH) Genetic and Rare Diseases Information Center (GARD).
https://rarediseases.info.nih.gov/diseases/7326/paraneoplastic-cerebellar-degeneration