Neuropathic pain, which has a prevalence of 7-10 percent, is caused by a lesion or disease of the somatosensory system. The somatosensory system allows for the perception of touch, pressure, pain, position, vibration, and temperature.
Symptoms of neuropathic pain depend on the type of nerves involved.
Muscle weakness, twitching known as fasciculations, cramps and muscle wasting are associated with motor nerve damage.
Loss of vibration sense and touch in the hands and feet and loss of position sense with a loss of coordination are characteristic of large sensory nerve damage. The patient may feel as if they are wearing gloves and stockings even though they are not.
Loss of ability to feel pain or temperature changes is due to small sensory fiber neuropathy. Pain is often worse at night and can interrupt sleep. The patient may feel severe pain from a light touch that would be painless to others, such as bedsheets over their limbs.
Excess sweating, intolerance to heat, loss of blood pressure regulation, and GI upset are symptoms of autonomic nerve damage in small nerve fibers.
The diagnostic work-up of neuropathic pain involves a history and physical exam as well as a detailed neurologic exam. During the history, the physician tries to gain insights about the onset, location, and distribution of the pain and any associated events that may have resulted in the neuropathic condition such as surgery or trauma. She/he will ask about the nature of the pain. Is it a shooting, burning, or aching sensation?
The physical exam attempts to identify sensory deficits using a variety of instruments that test for temperature sensation, touch sensation, and pain sensation.
Depending on the suspected cause, blood tests, imaging studies such as an MRI and electrodiagnostic studies including electromyography may be performed. Nerve or skin biopsies may be used to directly visualize nerve fibers.
The treatment of neuropathic pain depends on the underlying cause. Although patients with neuropathic pain often try over-the-counter pain medications, these drugs are not always effective. Topical pain medications that can provide relief to many patients with neuropathic pain include lidocaine patches, capsaicin patches, and prescription ointments and creams. Antidepressants such as tricyclics and serotonin-norepinephrine reuptake inhibitors can be effective for neuropathic pain and for treating the coincident anxiety and depression. Antiseizure medications, also known as anticonvulsants, are used frequently to treat neuropathic pain. The mechanism behind their effect is unclear.
Physical therapists can teach techniques for sitting, standing, and stretching that may help improve neuropathic pain.
Nerve blocks can be performed by an interventional pain management physician. Local anesthetic is injected with or without steroids near a peripheral nerve to block pain signals from the nerve to the brain. Depending on the severity and recurrence of symptoms, your physician may prefer to perform a series of injections.
If these therapies fail, a device that transmits electrical impulses to nerves, spinal cord, or brain can be implanted to interrupt pain signals emitted by damaged nerves.