Neuropathic Pain

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Definition

Complex type of pain initiated or caused by a primary lesion or dysfunction in the nervous system (IASP, 2012).

          Neuropathic pain is defined as pain arising as a direct consequence of a lesion or disease affecting the somatosensory system either at peripheral or central level. 

“pain initiated or caused by a primary lesion or dysfunction in the nervous system.” One example of neuropathic pain is called phantom limb syndrome.

Causes

Damage can be caused by trauma, surgery or disease processes including diabetes,infection (eg after shingles infection - post-herpetic neuralgia) and cancer.

Has a peripheral origin and may develop central sensitization but "primary afferent input is critical for maintaining neuropathic pain in peripheral nerve injury and distal polyneuropathy"

Pain may be generated in peripheral nerve, dorsal root ganglion,There are many reasons that patients may develop neuropathic pain. However, on a cellular level, one explanation is that an increased release of certain neurotransmitters which signal pain, combined with an impaired ability of the nerves to regulate these signals leads to the sensation of pain originating from the affected region. Additionally, in the spinal cord, the area which interprets painful signals is rearranged, with corresponding changes in neurotransmitters and loss of normally-functioning cell bodies; these alterations result in the perception of pain even in the absence of external stimulation. In the brain, the ability to block pain can be lost following an injury such as stroke or trauma. Over time, further cellular damage occurs and the sense of pain persists.

Trigeminal Neuralgia.
Pain following shingles (postherpetic neuralgia).
Diabetic Neuropathy - a nerve disorder that develops in some people with diabetes

Phantom limb pain                                                  

MS Multiple Sclerosis

Pain following chemotherapy.
HIV infection.
Alcoholism.
Cancer.
Atypical facial pain.
Various other uncommon nerve disorders.        

                                                

Central Causes of Neuropathic Pain

Peripheral Causes of Neuropathic pain

Compression myelopathy due to spinal stenosis • HIV myelopathy • Multiple sclerosis pain • Pain of Parkinson disease • Myelopathy after ischemia or radiation • Pain after stroke • Pain due to posttraumatic medulla spinalis injury • Syringomyelia

Acute and chronic inflammatory demyelinizating polyradiculoneuropathy • Alcohol induced polynerupathy • Chemoteraphy induced polyneuropathy • Complex regional pain syndrome • Entrapment neuropathies • HIV sensory neuropathy • Idiopathic sensorial neuropathy • Tumour infiltration of nerves • Neuropathy of nutrition deficiency • Painful diabetic neuropathy • Phantom pain of extremity • Postherpetic neuralgia • Plexopathy after radiation • Radiculopathy (cervical, thoracal, lumbosacral) • Neuropathy because of toxic exposure • Trigeminal neuralgia • Posttraumatic neuralgia • Peripheral nerve injury

 

Types

Entrapment Neuropathy

                     A trapped or pinched nerve at the neck, shoulder, elbow, wrist, hip, lower leg, or foot. Common examples of nerve entrapment include carpal tunnel syndrome, thoracic outlet syndrome (neck), or piriformis syndrome (hip).

Peripheral Neuropathy

                   Peripheral neuropathy first develops in the longest nerves of the body in a "glove and stocking" distribution to the hands and feet. There are numerous causes of peripheral neuropathy, including certain hereditary conditions, viral diseases, liver or kidney failure, and toxins, as well as diseases such as diabetes, vascular disease, and rheumatoid conditions.

Phantom Limb Pain

Phantom limb pain occurs in some people after the amputation of an arm or leg. Although the exact cause of phantom limb pain is unknown, it appears to result when the nerves and memories in the brain send faulty signals as the circuitry attempts to "rewire" itself.

Post Herpetic Neuralgia (PHN)

Post herpetic neuralgia (PHN) is a type of nerve pain that can occur following a viral infection of herpes zoster "shingles" in the nervous system. Post herpetic neuralgia aching or stabbing pain occurs in areas where the shingles rash developed. The skin in such areas may feel extra sensitive, especially in white-colored scars.

Post Traumatic Neuropathy

Post Traumatic Neuropathy occurs after injury or medical procedures, such as surgery or injection. Nerve pain symptoms may arise at the injury site and nerve path.

Trigeminal Neuralgia (TN)

Trigeminal neuralgia (TN) is a cause of severe pain in the face and jaw. Shocking, electric "lightening" pains typically precede dull aching pain. Trigeminal neuralgia usually affects only one side of the face. The exact cause of trigeminal neuralgia is unknown, but it develops where the trigeminal nerve is compressed, pinched, or irritated.

Clinical Features 

Patients often find it difficult to describe the quality of NP; it is outside their previous experience of pain. Sensory loss may be mild and overshadowed by allodynia (all stimuli producing pain), hyperalgesia and hyperpathia (delayed perception, summation and painful aftersensation). Rarely, (eg trigeminal neuralgia) there is no demonstrable sensory loss.There may be signs of sympathetic dysfunction, and
occasionally dystrophic changes. The onset of pain may be delayed, the commonest example being central poststroke pain (thalamic), which may start months or years after the initiating stroke. Pain is often of mixed nociceptive and neuropathic types, for example, mechanical spinal pain with radiculopathy or myelopathy. It is not generally recognised that nociceptive spinal pain can radiate widely, mimicking a root distribution. It can be difficult to identify the dominant pain type and treat appropriately. Such patients require careful examination, imaging and neurophysiological investigation.

Pathophysiology

The pathophysiological properties that are responsible for NP can be broadly categorised into five groups: ectopic impulse generation in damaged primary afferent fibres, fibre interactions, central sensitisation, disinhibition (failure or reduction of normal inhibitory mechanisms), and plasticity (degenerative and regenerative changes associated with altered connectivity).
1. The mechanisms of NP are substantially different to those of nociceptive pain.
2. Novel impulse generators develop at various sites, and these are not stimulus-dependent.
3. In peripheral nerve, it has been shown that ectopic impulse generation (EIG) develops as a result of the expression of abnormal sodium channels. This can be modified by neurotrophic growth factors (a potential target for new treatments).
4. Abnormal chemical sensitivities develop in damaged primary sensory neurons, notably to catecholamines. Whilst this can be readily demonstrated in experimental preparations, the clinical relevance remains uncertain.
5. Degenerative and then regenerative changes in the spinal cord may lead to aberrant connectivity, and possibly a permanently reorganised, irreversible state.
6. Damage at one level in the nervous system may lead to secondary pathophysiological changes at more rostral levels. This has important implications when targeting treatments for NP.

Assessment

Screening questionnaires are suitable for identifying potential patients with neuropathic pain, but further validation of them is needed for epidemiological purposes. Clinical examination, including accurate sensory examination, is the basis of neuropathic pain diagnosis. For more accurate sensory profiling, quantitative sensory testing is recommended for selected cases in clinic, including the diagnosis of small fiber neuropathies and for research purposes.

Step 1. A clinical history of disease or lesion of the somatosensory system suggests a possible diagnosis of neuropathic pain

Step 2. Confirmation by either clinically reproducible signs or investigations would suggest a probable diagnosis of neuropathic pain

Step 3. If the history, clinical examination and investigations are positive, this would support a definite diagnosis of neuropathic pain

Sensory examination - light touch, temperature, painful stimulus, vibration and proprioception. Motor testing tone, strength, reflexes and coordination. Look for autonomic changes in colour, temperature, sweating and swelling.

Examination of a Patient with Peripheral Neuropathic Pain shows a real patient with multiple mononeuropathy due to isolated peripheral nervous system vasculitis. He is suffering from neuropathic pain in his left hand and both legs. Functional assessment and sensory and motor examination of both upper and lower limbs is demonstrated. DN4 questionnaire assists with neuropathic pain assessment

Use when neuropathic pain is suspected

Management

Unfortunately, neuropathic pain often responds poorly to standard pain treatments and occasionally may get worse instead of better over time. For some people, it can lead to serious disability. A multidisciplinary approach that combines therapies, however, can be a very effective way to provide relief from neuropathic pain.

Other kinds of treatments can also help with neuropathic pain. Some of these include:

Physical therapy
Working with a counselor
Relaxation therapy
Massage therapy
Acupuncture

Medical management

Some neuropathic pain studies suggest the use of non-steroidal anti-inflammatory drugs, such as Aleve or Motrin, may ease pain. Some people may require a stronger painkiller, such as those containing morphine. Anticonvulsant and antidepressant drugs seem to work in some cases.If another condition, such as diabetes, is involved, better management of that disorder may alleviate the pain. Effective management of the condition can also help prevent further nerve damage.In cases that are difficult to treat, a pain specialist may use an invasive or implantable device to effectively manage the pain. Electrical stimulation of the nerves involved in neuropathic pain may significantly control the pain symptoms.

Physical therapy management

TENS is effective inthe treatment of painful peripheral neuropathy.Laser is another physical therapy agent that can be used in the treatment of neuropathic pain. Very low level of laser has been shown effective in patients with neuropathic pain .Neurostimulation techniques including transcranial magnetic stimulation (TMS) and cortical electrical stimulation (CES), spinal cord stimulation (SCS) and deep brain stimulation (DBS) have also been found effective in the treatment of neuropathic pain. In general, deep heating agents like ultrasound and short wave diathermy are not recommended in the treatment of neuropathic pain.

Exercising for just 30 minutes a day on at least three or four days a week will help you with chronic pain management by increasing:

Muscle Strength
Endurance
Stability in the joints
Flexibility in the muscles and joints

Keeping a consistent exercise routine will also help control  pain. Regular therapeutic exercise will help you maintain the ability to move and function physically, rather than becoming disabled by your chronic pain.

Physical therapy tackles the physical side of the inflammation, stiffness, and soreness with exercise, manipulation, and massage, but it also works to help the body heal itself by encouraging the production of the body's natural pain-relieving chemicals. This two-pronged approach is what helps make physical therapy so effective as a  pain treatment.

Resources

http://www.linxpt.com/Home/PatientEducationLibrary/tabid/9364/ctl/View/mid/15218/Default.aspx?ContentPubID=976

http://www.omicsonline.org/physical-therapy-modalities-and-rehabilitation-techniques-in-the-treatment-of-neuropathic-pain-jpmr.1000124.pdf