Breakthrough pain in cancer patients: Pathophysiology and treatment

Transient pain in cancer patients is relatively frequent and diverse in presentation and is associated with greater difficulties in achieving optimal control. Frequency, unpredictability, onset, severity, location, duration, and pain mechanisms are variable. Breakthrough pain may be spontaneous or induced by precipitations factors. Etiology is primarly neoplastic in most cases. The most common form of breakthrough pain is incident pain, caused by bone metastases. A rescue oral dose of a short half-life opioid can provide a means to treat breakthrough pain. When the onset of action of an oral dose may be too slow, a parenteral rescue dose may be effective. Oral transmucosal fentanyl has been reported to be another useful approach to the rapid onset of analgesia. Other treatments include the intermittent use of nonsteroidal anti-inflammatory drugs or nitrous oxide inhalation. Other adjuvant drugs, including antitussives, myolitic agents, and laxatives may be useful in reducing the frequency of recognized precipitating events. Episodes of neuropathic pain with a lancinating character my be alleviated by the regular use of different adjuvants. The spinal administration of local anaesthestics with an opioid may provide additional analgesia and permit the resumption of pain relief in patients unresponsive to spinal morphine administered alone. Pamidronate, radiotherapy and orthopedic intervention are useful in relieving pain from bone metastases. The results of neurosurgical techniques are often suboptimal. Further efforts to better define and evaluate transitory pain flares and develop treatment guidelines are warranted. Randomized controlled trials of breakthrough pain management are lacking. Such studies are to be strongly encouraged in order to provide a rational and scientific basis for treatment.