Management of Chronic Pain
DEFINITIONS OF PAIN AND RELATED TERMS
Pain: ‘an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage’ (The International Association for the Study of Pain, http://www.iasp-pain.org/AM/Template.cfm?Section=Pain_Definitions). This definition emphasizes that pain is not only a physical sensation but also a subjective psychological event. It accepts that pain may occur in spite of negative physical findings and investigations. Pain has sensory, cognitive and motivational-affective dimensions and has been described as a biopsychosocial experience, as illustrated in Figure 46.1. This must be taken into account when assessing and planning a treatment strategy for the patient with pain.
Acute pain: pain associated with acute injury (including surgery) or disease.
Pain medicine: the diagnostic and therapeutic activities of medical practitioners.
CLASSIFICATION OF PAIN
Pain may be classified according to its aetiology.
Nociceptive Pain
Visceral Pain
Visceral hyperalgesia: increased sensitivity in the painful organ. Pain threshold is lowered in some patients with functional gastrointestinal disease and patients complain of abdominal pain in response to normally innocuous stimuli of the gut.
Referred hyperalgesia from viscera, in which hypersensitivity is localized in the muscles and often associated with a state of sustained contraction. For example, patients with urinary colic typically display hypersensitivity in the muscles of the lumbar region.
Viscero-visceral hyperalgesia: pain in one visceral organ can be enhanced by pain in another visceral organ. Women with repeated urinary stones who were also dysmenorrhoeic manifested a higher number of colics than non-dysmenorrhoeic women.
Neuropathic Pain
Sympathetically Maintained Pain
In complex regional pain syndrome (CRPS) type 1, minor injuries, including mild soft tissue trauma or a fracture, precede the onset of symptoms without any overt nerve lesion (Fig. 46.2). CRPS type II develops after injury to a peripheral nerve. Pain is the prominent feature and is characteristically spontaneous and burning in nature and associated with allodynia (abnormal sensitivity of the skin) and hyperalgesia. Autonomic changes may lead to swelling, abnormal sweating and changes in skin blood flow. Atrophy of the skin, nails and muscles can occur and localized osteoporosis may be demonstrated on X-ray or bone scan. Movement of the limb is usually restricted as a result of the pain, and contractures may result. Treatment is directed at providing adequate analgesia to encourage active physiotherapy and improvement of function. In cases with sympathetically maintained pain, sympathetic nerve block may be part of this treatment strategy.
MANAGEMENT OF CHRONIC PAIN
Patients present with pain as a result of many different pathological processes. Some examples of common painful conditions are listed in Table 46.1.
TABLE 46.1
Some Common Painful Conditions
Malignant Aetiology
Primary tumours
Metastases
Nonmalignant Aetiology
Musculoskeletal
Back pain
Osteoarthritis
Rheumatoid arthritis
Osteoporotic fracture
Neuropathic
Trigeminal neuralgia
Postherpetic neuralgia
Brachial plexus avulsion
Radicular pain of spinal origin
Peripheral neuropathy
Chronic regional pain syndrome (CRPS)
Visceral
Urogenital pain
Pancreatitis
Post-surgery
Phantom pain
Stump pain
Scar pain
Post-laminectomy
Ischaemic
Peripheral vascular disease
Raynaud’s phenomenon/disease
Intractable angina
Headaches
Cancer treatment-related: e.g. post-surgery, post-chemotherapy, post-radiotherapy pain
Assessment
Pain History
Key elements in a pain history include:
location and radiation, either verbally or graphically using a pain diagram
intensity, e.g. verbal rating scale, visual analogue scale, faces pain scale (children)
quality, to determine possible somatic or neuropathic aetiology, e.g. burning, shooting; validated screening tools such as The Leeds Assessment of Neuropathic Symptoms and Signs (LANSS) pain scale can be used
current medication (analgesics and others)
basic psychological assessment to include mood, coping skills, pain beliefs and self-reported disabilities; a Hospital Anxiety and Depression (HAD) scale can assist as a screening tool but if full psychological evaluation is indicated, it should be performed either by a psychiatrist or by a clinical psychologist, preferably one who is an integral member of the pain management team
patient’s own ideas as to causation
impairment and functionality (Brief Pain Inventory)
Quality of Life, e.g. EQ-5D as a standardized instrument for use as a measure of health outcome