ABSTRACT: Understanding a patient's specific pain pathophysiology is the key to successful therapy. Nociceptive pain tends to respond to different treatments than neuropathic and psychogenic pain. Initial options for patients with chronic pain may include physical therapy; cognitive behavioral therapy; oral analgesics; and minimally invasive pain procedures, such as epidural corticosteroid injections. Certain medications (eg, tricyclic antidepressants and anticonvulsants) can be helpful in patients with neuropathic pain. Consider surgery for patients with refractory pain and for those whose pain has an identifiable cause that will respond favorably to surgery.
Pain is a significant public health concern. In a prevalence study conducted in Australia, 17% of men and 20% of women reported chronic daily pain.1 A US study found that 13% of the total workforce had lost productive time during a 2-week period because of a pain condition.2 Headache, back pain, and arthritis pain headed the list of causes.
Despite the growth of pain medicine as a specialty and the increasing number of pain centers, primary care physicians evaluate and treat most patients with pain. These patients can present numerous challenges.
Diagnosis is the first hurdle, since few reliable diagnostic tests are available for many pain conditions. Treatment options are often limited and may not be covered by medical insurance. There are sometimes legal issues regarding disability and liability. In general, patients with pain syndromes tend to consume a great deal of office time and resources.
In this 2-part article, we will explore the diagnosis and treatment of 3 pain syndromes. Here, following an overview of diagnostic principles and the available treatment modalities, we focus on osteoarthritis pain. In a coming issue, we will discuss the diagnosis and treatment of trigeminal neuralgia and radicular low back pain.
NEW EMPHASIS ON DIAGNOSIS
Diagnosis is crucial on several levels. First, it is essential to exclude progressive or serious conditions as soon as possible so that intervention can be timely. In addition, clarification of the type of pain (nociceptive or non-nociceptive) can increase the likelihood of successful treatment even in some previously intractable cases. Nociceptive pain (somatic and visceral), resulting from active stimulation of pain nerve endings caused by tissue damage or inflammation, tends to respond to different treatments than non-nociceptive (neurogenic and psychogenic) pain. (Table 1 lists clues to differentiating neuropathic from nociceptive pain). Also, the development of a lowered pain threshold (sensitization), which can occur peripherally as well as centrally, can be treated successfully if it is identified early.
The idea that understanding a patient's specific pain pathophysiology is the key to successful therapy is a relatively new one, but it is changing the face of pain management.3 Throughout this article, we will attempt to illustrate this principle.
OVERVIEW OF TREATMENT OPTIONS
Medication. Billions of dollars are spent each year on over-the-counter analgesics. For many patients with chronic pain, the limited effectiveness of these agents leads to overuse, adverse effects, and increased frustration. Overuse of NSAIDs can have serious GI and renal consequences and may affect cardiac health as well.
Opioids are effective in many patients with chronic pain, but they require judicious prescribing and monitoring.4 Opioids are all capable of producing adverse effects, including nausea, constipation, edema, pruritus, seizures, sleep disturbances, endocrine dysfunction, and tolerance, which can limit their use. High-dose opioids can also be associated with the development of opioid hyperal-gesia, the paradoxical response in which opioid treatment may worsen pain. The tendency of some patients to overuse prescription opioids for their euphoric properties and the increasing street value of some of these medications have dramatically altered the prescribing practices of many clinicians.
Many effective prophylactic medications are available for patients with chronic pain, especially if it is of neuropathic origin. These fall primarily into 3 main categories:
• Antidepressants, including tricyclic antidepressants and mixed norepinephrine(Drug information on norepinephrine) and serotonin reuptake inhibitors (duloxetine and venlafaxine). Selective serotonin reuptake inhibitors do not seem to have independent analgesic activity.
• Various agents, including antispasmodic medications, such as tizanidine and baclofen; muscle relaxants, such as orphenadrine; and neuroleptic/antiemetic medications, such as chlorpromazine(Drug information on chlorpromazine).
Minimally invasive procedures. In the hands of a skilled pain specialist with a background in interventional pain management, procedures have proved beneficial to many patients with chronic pain. Techniques include local nerve infiltration with lidocaine(Drug information on lidocaine), bupivacaine(Drug information on bupivacaine), and other local anesthetics. The addition of corticosteroid agents has been proposed as a way to prolong and strengthen the effect of these anesthetics through their ability to modify inflammation and block nociceptive C-fiber conduction.5 Epidural corticosteroid treatment, spinal cord stimulation, and intrathecal analgesic infusions have gained popularity. Although there is biochemical and clinical support for epidural corticosteroid therapy, randomized controlled trials are needed to determine which patients will benefit the most from this technique. Trigger point injections may be no more effective for pain conditions than placebo transcutaneous electrical nerve stimulation, although there are avid proponents of the technique.
Behavioral medicine techniques. Relaxation training, biofeedback, and cognitive-behavioral training can be helpful in patients with chronic pain. Two key requirements are skilled practitioners and motivated patients.
Surgery. This is an attractive option for patients with a suspected mechanical cause of pain. Often, however, well-intentioned surgical procedures may prove unhelpful, even with excellent morphological outcome. Thus "failed-back" and "failed-neck" patients abound. For patients with truly intractable pain, neurolysis, gangliectomy, dorsal root entry zone (DREZ) lesioning, and other invasive procedures can be considered. Neural stimulation helps some patients, including those with persistent radicular pain after lumbosacral spine surgery.
Management of psychiatric comorbidities. It is essential to identify and address the psychiatric comorbidities found in many patients with chronic pain. Many are significantly frustrated by their illness, sometimes to the point of suicidal ideation. These issues must be addressed, ideally by a psychologist or a psychiatrist with experience in chronic pain management. Secondary gain must be explored when this possibility exists. Substance abuse potential should also be monitored. Table 2 lists possible psychiatric accompaniments in patients with chronic pain.
OSTEOARTHRITIS OF THE KNEE
Osteoarthritis is the most prevalent form of arthritis. It is projected that more than 59 million persons in the United States (18% of the population) will have osteoarthritis by 2020.6 This noninflammatory rheumatologic condition is associated with nociceptive pain. One of the joints most commonly affected is the knee. Osteoarthritis of the knee poses the highest associated risk of mobility disability (assistance needed with ambulation) compared with other medical disorders in persons 65 years and older.
The pathogenesis of osteoarthritis is characterized by alterations in articular cartilage. Persons with osteoarthritis also have changes in subchondral bone, menisci, ligaments, synovium, and periarticular muscles.7 Risk factors for osteoarthritis include:
• Genetic factors.
• Congenital and traumatic deformities associated with malalignment.
• Female sex.
• Occupational activity.