NEUROPATHIC PAIN

SUMMARY:  Pain concepts and terminology are continually evolving as its complexity is gradually unravelled.  Pain that is generated by an irreversibly injured nerve may be exacerbated by unpleasantly altered sensations beyond the anatomical area served by that nerve. The functional impairments caused by neuropathic pain need to be systematically analysed.

Terminology

Not infrequently, clinicians and medical expert witnesses confuse and misuse terms for disordered sensation and nerve-generated pain.  The following classification and official definitions ¹ are offered for reference: 

Pain

Pain is defined as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." 

Pain Threshold is "the least experience of pain which a subject can recognize" and

Pain Tolerance Level "the greatest level of pain which a subject is prepared to tolerate."

For clarification, these three concepts are entirely subjective and have no objective criteria. 

Disorders of sensation

Hyperesthesia ('increased feeling') is defined as "increased sensitivity to stimulation, excluding the special senses" Paresthesia ('beyond feeling') is "an abnormal sensation, whether spontaneous or evoked" that is not unpleasant whereas Dysesthesia ('impaired feeling') is "an unpleasant abnormal sensation, whether spontaneous or evoked". Particular types of hyperesthesia and dysesthesia are

Hyperalgesia ('increased pain') "an increased response to a stimulus which is normally painful",

Hyperpathia, ('increased suffering') "a painful syndrome characterized by an abnormally painful reaction to a stimulus, especially a repetitive stimulus, as well as an increased threshold" and

Allodynia, ('other pain') "pain due to a stimulus which does not normally provoke pain".  Thus, allodynia involves a change in quality of sensation, whether touch or heat or cold, for example. 

Hypoesthesia ('decreased feeling')  in contrast means "decreased sensitivity to stimulation, excluding the special senses"  and

Hypoalgesia ('decreased pain') "diminished pain in response to a normally painful stimulus" of which

Analgesia ('no pain') is complete loss of pain sensation,  namely "absence of pain in response to stimulation which would normally be painful."

Pain arising in nervous tissue

Neuropathic Pain ('nerve disease') is "initiated or caused by a primary lesion or dysfunction in the nervous system."

Central Pain is "initiated or caused by a primary lesion or dysfunction in the central nervous system" and the equivalent in the peripheral nervous system is called

Peripheral Neuropathic Pain. More temporary disturbances are referred to as

Neurogenic Pain, ('caused by nerves') "initiated or caused by a primary lesion, dysfunction, or transitory perturbation in the peripheral or central nervous system."

('nerve pain') is "pain in the distribution of a nerve or nerves", not reserved for paroxysmal pains as is common European usage.

Neuritis ('nerve inflammation') is correctly "inflammation of a nerve or nerves.

Prevalence

2-3% of the population suffer from neuropathic pain. 

Pathology

Pain that is generated by an irreversibly injured nerve may be exacerbated by unpleasantly altered sensations beyond the anatomical area served by that nerve.

Our understanding of the chronic effects of physical and psychological injury on bodily sensations remains fragmentary and rudimentary.  "It's all in the mind" and "injured soft tissues remain unhealed" are equally inaccurate as models. 

Changes in the microscopic anatomy and physiology and functioning of nerves, ganglia and spinal cord accompanying the development of post-traumatic neuropathic pain are complex and currently being elucidated further. ^2a

Management

In the present state of knowledge, there is no way to prevent the development of neuropathic pain ³ nor reliably and predictably to treat established neuropathic pain. ⁴

Functional Impairment

The functional impairments caused by neuropathic pain need to be systematically analysed.

Copyright © 2008 Electronic Handbook of Legal Medicine