There are several configurations of central lesions that damage the sensory system and produce severe pain. Deafferentation of secondary neurons in the posterior horns or of sensory ganglion cells that terminate on them may cause the deafferented cells to become continuously active and, if stimulated by a microelectrode, to reproduce pain. In the patient whose spinal cord has been transected, there may be intolerable pain in regions below the level of the lesion. It may be exacerbated or provoked by movement, fatigue, or emotion and projected to areas disconnected from suprasegmental structures (akin to the phantom pain in the missing part of an amputated limb). Here, and in the rare cases of intractable pain with lateral medullary or pontine lesions, loss of the descending inhibitory systems seems a likely explanation. This may also explain the pain of the Dejerine-Roussy thalamic syndrome described in the next chapter. Altered sensitivity and hyperactivity of central neurons are alternative possibilities.
Further details concerning the subject of neuropathic pain can be found in the older but still informative writings of Scadding and of Woolf and Mannion.
It is not unusual for patients with depression to have pain as a dominant symptom. As emphasized previously, most patients with chronic pain of all types are depressed. Wells and colleagues, in a survey of a large number of depressed and chronic pain patients, have corroborated this clinical impression. Fields (1991) has elaborated a theoretical explanation of the overlap of pain and depression. In such cases, one is faced with an extremely difficult clinical problem— that of determining whether a depressive state is primary or secondary. Complaints of weakness and fatigue, depression, anxiety, insomnia, nervousness, irritability, palpitations, etc., are woven into the clinical syndrome, attesting to the prominence of a psychiatric disorder. In some instances the diagnostic criteria for depression cited in Chap. 48 provide some insight, but in others it is impossible to make this determination and may not be necessary as depression and pain are so often coincident. Empiric treatment with antidepressant medication or, failing this, with electroconvulsive therapy is one way out of the dilemma.
Intractable pain may also be the leading symptom of both somatization and conversion reactions. Experienced physicians are familiar with the patient who has undergone multiple surgical procedures to address painful complaints (Briquet disease). The recognition and management of this group of disorders are discussed in Chap. 47.
The desire for compensation (e.g., workman’s compensation, disability status) is usually colored by persistent complaints of headaches, neck pain (whiplash injuries), low back pain, and other painful conditions. The question of ruptured disc is often raised, and laminectomy and spinal fusion may be performed (sometimes more than once) on the basis of dubious radiologic findings. Long delay in the settlement of litigation, allegedly to determine the seriousness of the injury, only enhances the symptoms and prolongs the disability. The medical and legal professions have no certain approach to such problems and often work at cross-purposes. We have found that a frank, objective appraisal of the injury, an assessment of any psychiatric problem, and encouragement to settle the legal claims as quickly as possible work in the best interests of all concerned. Although hypersuggestibility and relief of pain by placebos may reinforce the physician’s belief that there is a prominent factor of hysteria or malingering (see Chap. 47), such data are difficult to interpret.