Paraneoplastic neurologic syndrome (PNS) represents the remote effects of cancer on the nervous system. They can affect any part of the nervous system. Such syndromes usually occur as the first sign of a tumor or lead to its detection.
Rarely, they are seen in the course of an oncologic disease; small-cell lung cancer, ovary, breast, and non-small-cell lung cancer are the malignant neoplasms most frequently associated with PNS .

The most frequent entities are paraneoplastic cerebellar degeneration (PCD) and sensory neuronopathy (SN). Limbic encephalitis constituted another major entity, followed by paraneoplastic encephalomyelitis and brainstem encephalitis. Multifocal presentation is also present.
The most frequent clinical findings are subacute onset of moderate or severe ataxia with truncal or limb involvement. Dysarthria and nystagmus were less commonly observed.

Survival is usually influenced by the oncologic disease, but PNS can cause severe disability and may be fatal.
Onconeural antibodies (e.g., anti-hu, anti-yo) as biological markers of paraneoplastic neurological syndromes have proved very useful in the diagnosis of a given neurological syndrome as paraneoplastic.

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Adapted from Giometto V et al. Paraneoplastic Neurologic Syndrome in the PNS Euronetwork Database. Arch Neurol. 2010;67(3):330-335. Internet. Accessed on July 5, 2016.