ABC of palliative care: Difficult pain problems

Roughly 80-90% of pain due to cancer can be relieved relatively simply with oral analgesics and adjuvant drugs in accordance with the World Health Organisation's guidelines.The remaining 10-20% can be difficult to treat.The terminology used to describe pains that are not easily controlled with opioid analgesics is confusing.It is rarely the case that pain can be described as non-responsive or resistant to opioid analgesics because this implies an all or nothing phenomenon.Usually, pain in cancer responds at least partially to opioids, and a preferable term is "opioid-poorly-responsive pain."A pragmatic clinical definition is that such pain is inadequately relieved by opioid analgesics given in a dose that causes intolerable adverse effects despite optimal measures to control them.The most common example is neuropathic pain. Neuropathic painNeuropathic pain arises from damaged nervous tissue, whereas nociceptive pain results from actual or potential tissue damage.Neuropathic pain may be produced by a tumour infiltrating or compressing nervous tissue, either centrally or peripherally, and may also be caused by surgery, radiotherapy, chemotherapy, or viral infection.Patients may describe the pain as burning, stabbing, stinging, or aching.It may be felt superficially or deeply and be constant or intermittent.It may be spontaneous or precipitated by various stimuli, some of which are not normally painful (allodynia), such as a light touch or cold.