Neuropathic pain can result from either efferent activity (sympathetically maintain pain) or afferent activity stoppage (deafferentation pain).
Peripheral nerve injury or failure can result in neuropathic pain. Here are a few examples:
Mononeuropathies (involve a single nerve [eg, carpal tunnel syndrome, radiculopathy owing to a ruptured intervertebral disc]) (involve a single nerve [ie, carpal tunnel syndrome, radiculopathy owing to a ruptured intervertebral disc]) (involve a single nerve, such as carpal tunnel syndrome or radiculopathy caused by a ruptured intervertebral disc).
Trauma, inflammation
Plexopathies (involve multiple nerves inside a particular neural plexus. Often caused by trauma, inflammation, or nerve compression, as by a tumor) (involve several nerves inside a particular neural plexus. Generally caused by trauma, inflammation, or nerve compression, as by a tumor) (involve several nerves inside a single neural plexus. Usually caused by trauma, inflammation, or nerve compression, such as from a tumor)
Polyneuropathies (involve multiple nerves, usually across the body; often caused by various metabolic disorders. paraproteinemias, toxic exposures [ie, alcohol, chemotherapy], hereditary predisposition, or, in rare cases, immune-mediate pathways) (involve several nerves, commonly across the body; often caused by various metabolic problems, paraproteinemias, toxic exposures [ie, alcohol, chemotherapy], inherited susceptibility, or, in rare cases, immune mediate pathways)
Neuropathic pain is complex and involves modifications
At the peripheral nociceptor and nerve level
It is found in the dorsal root ganglion.
Central nervous system nociceptive pathways and terminal structures (CNS)
At the level of the peripheral nerve and nociceptor, injury promotes inflammation as well as activation and over-representation of cation channels, particularly sodium channels. These changes reduce the activation threshold and increase sensitivity to unpleasant stimuli.
In chronic situations, the peripheral nerve constantly delivers Nociceptive ectopic impulses to the CNS. This constant barrage of peripheral nociceptive information alters receptive nociceptors (central sensitization); they are primed, interpret pain from mild stimuli (including nonpainful stimuli [allodynia]) as major pain, and interpret that pain as emanating from a broader area than it actually does. These changes can reverse, at least temporarily, if the peripheral nociceptive input is inhibited.
Central neuropathic pain
Central neuropathic pain syndromes (pain induced by somatosensory pathway dysfunction in the CNS) can arise from any CNS lesion, but they are most commonly associated with a stroke, spinal cord injury, or a multiple sclerosis demyelinating plaque.
To call central neuropathic pain, the pain must occur in the clinically affected area of the CNS lesion; however, it does not have to involve the entire affected area. Central neuropathic pain occurs only when the spinothalamic tract (pinprick, temperature sensation) malfunctions.
If pinprick and temperature sensations in the suspected central neuropathic pain region are normal, another source of pain consider. The most common source of pain in neurologically impaired patients is musculoskeletal discomfort (eg. shoulder pain related to arm paresis after a stroke or an upper extremity overuse syndrome in wheelchair-bound patients with a spinal cord injury).
An interruption in peripheral or central afferent neural activity causes deafferentation discomfort. Here are a few examples:
Postherpetic neuralgia
The ache in the center (pain after CNS injury). Phantom limb ailment (pain felt in the region of an amputated body part)
The mechanics are unknown, however, they may involve central neuron sensitization, with lower activation thresholds and enlarged receptive fields.
Overactivity of the sympathetic nervous system has link to neuropathic pain syndromes. Although sympathetic overactivity does not cause neuropathic pain, it can exacerbate its clinical features and intensity.
The pain that results is known as sympathetically maintained pain, and it is caused by efferent sympathetic activity. Complex Regional Pain Syndrome is characterized by sympathetically maintained pain. Sympathetic pain may also present in other types of neuropathic pain.
What causes sympathetic overactivity in some neuropathic pain states but not others is unknown. The most plausible mechanisms include faulty sympathetic-somatic nerve connections (phases), local inflammatory changes, and spinal cord abnormalities.
Symptoms and Signs of Neuropathic Pain
Dysesthesias (random or induced searing pain with a lancinating component) are prevalent, but pain can also be deep and agonizing. Other sensations that may arise include hyperesthesia, hyperalgesia, allodynia (pain induced by nonnoxious stimuli), and hyperpathia (a particularly unpleasant, excessive pain reaction).
Patients may refuse to move the painful portion of their body, resulting in muscle atrophy, joint ankylosis, bone loss, and decreased mobility.
Because the CNS has been sensitized and altered, symptoms usually persist after the underlying cause has been resolved (assuming one was present).
Diagnosis of Neuropathic Pain Clinical Examination
The characteristic symptoms of neuropathic pain are present when nerve injury is known or suspect. The cause (amputation, diabetes, or compression, for example) can obvious. If this is not the case, the diagnosis is typically predicated on a description of the symptoms; nevertheless, those descriptors (such as searing) are neither sensitive nor specific for neuropathic pain.
As a result, additional tests, such as a neurologic exam and electrophysiologic studies, are require to confirm the diagnosis and identify the injury nerve. Pain that is relieved by sympathetic nerve block is known as sympathetically maintained pain.
Treatment for Neuropathic Pain
Multimodal therapy (eg, physical methods, antidepressants, antiseizure drugs, psychotherapeutic methods, neuromodulation, and sometimes surgery)
The first step in treating neuropathic pain is confirming the correct diagnosis and addressing treatable causes (eg, herniated disk, carpal tunnel syndrome). In addition to drugs, mobilization and physical therapy are need to desensitize. Areas of allodynia and prevent trophic changes, disuse atrophy, and joint ankylosis.
Psychological difficulties can treat from the start of treatment. Anxiety and depression is treat properly. If the pain persists, neural blocking may be helpful. When first-line drugs fail to improve dysfunction, patients is benefit from a pain clinic’s holistic approach.
Neuromodulation (spinal cord or peripheral nerve stimulation) is particularly effective in treating neuropathic pain.
Several drug types are helpful, but complete relief is rare, thus it is vital to set moderate expectations. The purpose of pharmacologic pain management is to reduce the severity of neuropathic pain.
Opioid analgesics can provide some relief, but they are frequently less effective than in the treatment of acute nociceptive pain and entail the risk of dependence; side effects may limit appropriate analgesia.
Antidepressants and epileptic drugs are examples of adjuvant analgesics
Most commonly used to treat neuropathic pain, and evidence from randomized trials supports its usefulness (1; see table Drugs for Neuropathic Pain).
For this reason, gabapentin is one of the most regularly use drugs. The dose its greater than 600 mg orally three times per day for adequate analgesia, and many people require a higher amount. The highest suggested dosage is 1200 mg three times a day orally.
Pregabalin 100mg is the same as gabapentin but has more stable pharmacokinetics; two daily dosages are just as effective as three daily doses and result in better compliance. The recommend daily dose is at least 300 mg administer orally (eg, a starting dose of 75 mg 2 times a day, increase to 150 mg 2 times a day within 1 week). Neuropathic pain problems may require up to 600 mg daily.
Despite the fact that the two drugs have a similar underlying mechanism of action, some persons who do not respond well or tolerate gabapentin respond well or tolerate pregabalin, and vice versa (binding to the alpha-2 delta ligand of the presynaptic calcium channel, which modulates nociceptive signaling).
Tricyclic antidepressants (amitriptyline, nortriptyline, and desipramine) work primarily by inhibiting serotonin and norepinephrine reuptake. Typical analgesic doses (75-150 mg orally once daily) are insufficient to alleviate sadness or anxiety.
Anticholinergic and adrenergic side effects typically limit the appropriate dose. Secondary amine tricyclic antidepressants (nortriptyline and desipramine) have fewer negative effects than tertiary amine tricyclic antidepressants (amitriptyline and desipramine) (amitriptyline).
Pregalin 50mg appears to help with diabetic neuropathic pain, fibromyalgia, chronic musculoskeletal pain (particularly low back pain), and chemotherapy-induced neuropathy. Effective doses for depression, anxiety, and pain treatment are similar.
Venlafaxine’s effects and mechanism of action are similar to those of duloxetine
Topical medicines and a patch containing lidocaine can effective for peripheral symptoms.
Other potentially effective treatments include:
For certain types of neuropathic pain, spinal cord stimulation with an epidurally implant electrode is use (eg, chronic leg pain after spine surgery)
Electrodes is inserting along peripheral nerves and ganglia to treat certain persistent neuralgias (peripheral nerve stimulation)
Except in a few cases of complex regional pain syndrome, sympathetic blockade is usually ineffective.
Neural blockage or ablation (radiofrequency ablation, cryoablation, chemoneurolysis)
Electrical nerve stimulation via the skin (TENS)