24A. Paraneoplastic nervous system diseases

Definition and epidemiology

Paraneoplastic nervous system diseases occur in 1 – 3% of patients with cancer. They often develop before the cancer diagnosis. They usually occur because the tumour expresses antigens which are structurally similar to antigens on neurons (molecular mimicry). Antineuronal antibodies are often present in the serum and CSF.

It’s important to recognise these diseases because they can give earlier diagnosis of the tumour and because their prognosis is better the earlier the treatment is initiated. These conditions are usually treated by steroids and plasma exchange.

The most common underlying cancers are:

  • Neuroendocrine tumours
    • Small cell lung cancer
    • Ovarian cancer
    • Prostate cancer
  • Breast cancer
  • Lymphoma

We can classify them according to whether they’re associated with antibodies against neuronal surface antigens or nuclear antigens:

  • Neuronal nuclear antibody-associated types
    • Antibodies against nuclear antigens
    • Respond poorly to therapy
    • Includes
      • Paraneoplastic cerebellar degeneration
      • Paraneoplastic sensory neuronopathy
      • Limbic encephalitis caused by anti-Ma2
  • Neuronal surface antibody-associated types
    • Antibodies against surface antigens
    • Respond better to therapy, especially plasma exchange
    • Not always causes are paraneoplastic, can be autoimmune as well
    • Includes
      • Anti-NMDA receptor encephalitis
      • Limbic encephalitis caused by other antibodies

Anti-NMDA receptor encephalitis

This is a type of limbic encephalitis which is caused by antibodies against the NMDA receptor. There is almost always an underlying ovarian teratoma. The condition usually presents as behavioural changes, memory problems, seizures, cognitive decline in young women or children. It has a good response to therapy.

Anti-Ma2 encephalitis

This is another type of limbic encephalitis which is caused by anti-Ma2 antibodies. There is often an underlying testicular cancer. It presents with memory deficits, seizures, and irritability. It has a poor response to therapy.

Paraneoplastic sensory polyneuropathy

This is a severe neuropathy characterised by asymmetric paraesthesia and severe pain of the upper limbs. It has a poor response to therapy.

Paraneoplastic cerebellar degeneration

This is a subacute cause of cerebellar degeneration, which presents with cerebellar symptoms. It has a poor response to therapy.

Dermatomyositis

Dermatomyositis can be paraneoplastic as well. Described in topic 1A.


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23B. Nervous system metastases

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24B. Symptoms of raised intracranial pressure

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