Neuropathic pain is caused by damage to- or dysfunction of- the peripheral and central nervous system, rather than stimulation of pain receptors. It can involve any level of the nervous system and in neuropathic pain the nerve fibres may be damaged, dysfunctional or injured. The impact of injury includes a change in nerve function both at the site of injury (e.g. the spinal cord) and areas around the injury. This leads to incorrect signals being sent to the brain. The brain perceives that these signals are coming from pain receptors in the skin or organs where in fact this is not the case. Phantom pain following limb amputation is a good example of this.
People commonly use abnormal adjectives to describe painful and non-painful sensations such as ‘shooting’, ‘burning’, ‘tingling’ and ‘numbness’. In people with neuropathic pain, there are three types of changes that can occur: painful symptoms, visible skin changes and loss of sensation.
Neuropathic pain commonly results in ‘spontaneous’ pains. Some of these sensations appear to have a ‘life of their own’ and are bizarre. Sensations include abnormally painful responses to an ordinary physical stimulus (evoked pain); and spontaneous pain – which occurs in the absence of a stimulus. There are two types of spontaneous pain: continuous and paroxysmal.
Evoked pains are usually exaggerated responses to innocuous events that do not cause pain in people with ‘normal’ pain pathways:
Paraesthesia and dysaesthesia – absence or impairment of the senses especially touch
Hyperpathia – a prolonged duration of pain following a painful event.
Hyperalgesia – hypersensitivity to mildly painful events – knocks, for instance.
Other sensations can include physical contact in one area of the skin resulting in painful sensations in another (trigger zone pain), or pain that radiates down a whole leg or arm (referred pain).
In people with neuropathic pain, there may be visible changes in the skin in the area that overlies the painful area. Mechanisms underlying these changes that may accompany neuropathic pain are not well understood and are complex. The expected changes include the skin being pinker or redder than other areas; or more blue, mottled and dusky-looking. The changes that occur are largely due to alterations in blood flow. As well as colour changes; the skin can look waxy, dry, puffy or swollen with a reduction in hair and nail growth.
Areas affected by neuropathic pain can be numb to touch. Nerve damage from injury or disease processes can lead to loss of normal sensation. The nerves that are the most prone to damage (from diseases like diabetes) are those carrying temperature sensations; and hence the assessment involves testing for sensation, pain and temperature. The loss of normal input from the anaesthetic area may cause a failure of the normal gating process and promote central sensitisation in an effort to gain information from the affected area. Such amplification may result in the paroxysmal presentation of pain in a non-sensate area.
A diagnosis is usually made using a combination of the patient’s report, a clinical examination and sensory nerve testing. Often, quantitative sensory testing is performed. Although these tests might highlight areas of abnormal sensation, the tests themselves cannot prove or disprove that a person is suffering with pain caused by the nerve damage.(Eur J Neurol 11(3):153-62).
Before considering what is available in terms of managing this type of pain, it is important to stress that any underlying condition that may be implicated should be assessed and managed. For instance, mechanical pressure (e.g. by spinal discs on spinal roots) causing the neuropathic symptoms may require surgery. Improvements in diabetic control can improve symptom progression in diabetic neuropathy but cannot reverse damage.
It may be useful to consider two approaches to managing pain of neuropathic origin:
Non-pharmacological Treatment of Neuropathic Pain)
Physical methods- desensitisation, mirror-box therapy, rehabilitative physiotherapy
Psychological techniques such as Mindfulness, ACT, CBT
Non-opioid analgesics and NSAIDs
IV management (lidocaine, ketamine)
Complex, multimodal treatment approaches e.g. residential intense pain managemnet programs
Invasive techniques – nerve blocks, deinnervation, etc
The following may be useful in identifying what should be considered in managing people with neuropathic pain:
Clinically, it is important to stress that neuropathic pain is a difficult problem, often resistant to multiple therapies; and requires patience and understanding by both the person affected and health care professional. Treament is best with a collaborative approach to therapy; and ideally, there should be frequent reassesment of treatment response, disease progression and careful evaluation of quality of life indicators.