The treatment of chronic pain relies on pharmacologic and nonpharmacologic methods. Commonly treated chronic pain syndromes include osteoarthritis, nonsurgical intervertebral disk disease, and laminitis. Some chronic pain responds to drugs used to treat acute pain, such as opioids and NSAID; however, other types of chronic pain require the addition of novel drugs such as gabapentin, tramadol, acetaminophen, and amantadine. Regardless of the etiology or the species, chronic pain is itself a dynamic disease process requiring careful assessment and frequent reassessment. Therapy is rarely monomodal, and adjustments in therapy are necessary over time.
The nonpharmacologic treatment of chronic pain depends on the underlying cause and the species. Among these therapies are acupuncture, rehabilitation, nutraceutical supplements, low-level laser, massage, transcutaneous electric nerve stimulation, and herbal supplements. The body of literature critically examining these is relatively small. (Also see Complementary and Alternative Veterinary Medicine).
The nonpharmacologic goals for managing osteoarthritis pain include increasing mobility, limiting disease progression, and possibly facilitating tissue repair within the joint. Weight control or reduction and mild to moderate daily exercise are beneficial. Excessive and strenuous exercise should be avoided, because it may further strain the joints and exacerbate pain, thus limiting the ability to routinely exercise. Providing warmth during cold and damp weather and extra bedding or padding may also improve comfort. Surgical removal of bone fragments and osteochondritic lesions and restoration of joint stability is often necessary to slow the progression of disease and reduce pain. Joint replacement or arthrodesis may be indicated in severe cases. Orthotic bracing may be beneficial in small-animal patients when surgical intervention is not appropriate. A number of studies using chondroprotective agents such as polysulfated glycosaminoglycans, chondroitin sulfate, glucosamine, and hyaluronic acid suggest a benefit by stimulating cartilage matrix synthesis and inhibiting enzymatic degradation of cartilage. However, the efficacy of these agents may vary with specific product used, route of administration, and underlying conformational, pathologic, and neurologic issues. Recent work in regenerative medicine, including the use of autologous adult stem cells, may prove highly effective as well. Finally, acupuncture and rehabilitation therapy have been used to treat chronic osteoarthritis pain in a number of veterinary species with promising results.
Cancer pain presents a unique clinical challenge. Like other forms of chronic pain, it does not always respond adequately to common therapies. Opioids remain a cornerstone of treatment and are usually one part of a multimodal plan. Other analgesics include NSAID, tramadol, acetaminophen (in dogs), and amantadine for its ability to decrease wind-up. The combination of an opioid and an NSAID is routinely used because of their synergistic analgesic effect. Recently, bisphosphonates have been used to treat osteolytic pain associated with bony metastasis. Pamidronate is the synthetic analog of inorganic pyrophosphate. It has proved useful in pain palliation because of its ability to adsorb to bone mineral matrix, inhibit pathologic lysis induced by osteoclasts, and delay progression of bony metastatic lesions.
Like all chronic pain syndromes, cancer pain management requires frequent assessment and reassessment combined with appropriate adjustments in therapy.
Last full review/revision July 2011 by Peter W. Hellyer, DVM, MS, DACVA; Patrice M. Mich, DVM, MS, DABVP (Canine/Feline), DACVA