Peripheral Nervous System
Introduction
Long term damage to the nerves outside the brain and spinal cord (peripheral neuropathy) after treatment for cancer is usually due to therapeutic/chemotherapy agents.
It is usually caused by chemotherapeutic agents used in the treatment of cancer1 and has an overall incidence of 30-40% in patients treated with chemotherapy2.
Chemotherapy Induced Peripheral Neuropathy (CIPN)
This complication, also known as chemotherapy-induced peripheral neuropathy (CIPN), can be associated with1:
- Vinca Alkaloids (Vincristine and rarely Vinblastine)
- Platinum compounds (Cisplatinum and rarely carboplatin, oxaliplatin)
- Taxanes (paclitaxel i.e. taxol and rarely docetaxel)
- Thalidomide (used as anti-angiogenic agent)
Different agents affect different types of peripheral nerves3:
- Small fibre nerves – unmyelinated axons made primarily of microtubules; includes pain and temperature fibres
- Large fibre nerves – myelinated axons made primarily of neurofilaments; includes position and vibration fibres, and motor neurons
Vincristine and paclitaxel mostly affects small fibres, while cisplatin affects large fibres3.
Other Causes:
Peripheral nerve damage can also occur after surgery or direct damage from a tumor pushing on a nerve.
It would be very unusual radiation therapy (RT) to cause peripheral neuropathy, as peripheral nerves are relatively radioresistant due to low rates of DNA replication4.
Signs and Symptoms:
Signs and symptoms of peripheral neuropathy include1:
- Burning or numbness in the hands and feet
- Extreme sensitivity to touch
- Sharp shooting pains
- Loss of balance and/or coordination
- Loss of reflexes
- Muscle weakness
Sensory symptoms arise much sooner than motor symptoms because sensory neurons and pain fibres are less myelinated and are therefore more susceptible than motor nerves to the toxic effects of chemotherapeutic agents.
Autonomic nerves are poorly myelinated and autonomic symptoms may manifest early on as well5.
Long, distal axons are affected first, as they are the furthest away from the cell body and are most vulnerable to the disruption of the nutritional cytoplasmic supply chain. Therefore CIPN manifests in toes and feet as paresthesias and pain early on, spreading proximally as the disease progresses5.CIPN induced pain can seriously affect quality of life1.
