Neuropathic pain is the result of an injury or malfunction in the peripheral or central nervous system. Tissue injury includes impairment of pain receptors, nerve fibers carrying pain from peripheral receptors to spinal nerves (neurons). Also chronic neuropathic pain is end result of malfunction of spinal nerves carrying pain impulses to brain. Deteriorating pain transmitting system become dysfunctional and sends incorrect signals to other pain centers. Causes and pathophysiology of neuropathic pain is not yet comprehended for prevention. “Windup theory” and NMDA receptor changes at peripheral receptors and within spinal cord is been investigated in details. Immune response and immune complex were discovered in animal studies at and near peripheral nerve receptors and injure tissue. Immune complex were observed in peripheral tissues with neuropathic pain. Immunotherapy may be future treatment option if cause is found.
Neuropathic pain is either secondary to cancer or non cancer etiology.
Epidemiologic Studies : Epidemiological studies have revealed following Incidence and Prevalence of Chronic Pain
- 70 Million Adults in United States suffer with chronic pain.
- 35% of population suffers with chronic back pain and spine pain.
- 10% of population in USA are diagnosed of arthritis.
- 12% suffer with chronic joint syndrome includes 10% of arthritis.
- 70% of adult suffer with low back pain at least once or more and common age group is 35 to 55 years of age.
Classification and Types of Chronic Neuropathic Pain
Chronic Cancer Neuropathic Pain
- Complex Regional Pain syndrome I (RSD)
- Complex Regional Pin syndrome II (Causalgia)
Chronic Non Cancer Neuropathic Pain
- Complex Regional Pain syndrome I (RSD)
- Complex Regional Pin syndrome II (Causalgia)
Pathophysiology of Chronic Neuropathic Pain
- Nerve fiber injury – leads to abnormal secretion of neuro transmitters in the spinal cord where signals are transmitted to pain centers in midbrain, thalamus a cortex. These nerves now misfire and cause pain.
- Pain also felt in adjacent normal tissues (hyperalgesia).
- Neuropathic pain is observed in chronic non – cancer and also in cancer pain.
- Neuropathic pain when involves peripheral and central autonomic nervous system causes chronic intractable pain also called Complex Regional Pain Syndrome (CRPS).
- Sympathetic system is one of the divisions of autonomic nervous system and predominantly involved with CRPS.
- Sympathetic neuropathic pain may be exhibited as allodynia, hyperalgesia or hyperpathia.
Pathophysiology Of Chronic Neuropathic Pain Secondary To Cancer:
- Tumor tissue infiltration into the nerve fibers: Causes nerve entrapment.
- Pressure on nerves: By tumor mass may compressed nerve from outside. Cancer pain may cause pressure on soft tissue and nerves by increase size of tumor.
- Spinal canal infiltration: Bone metastasis of vertebral column caused nerve compression, infiltration or pressure displacement of structure of spinal canal e.g. spinal cord or spinal nerves. Pain secondary to cancer in most of the case are mixed initially nociceptive and later neuropathic. Initial injuries to nerves lead to nociceptive pain and later as pain continuous and become central turns in to neuropathic pain.
Pathophysiology Of Chronic Neuropathic Pain Caused By Non-Cancer Pathology:
After tissue injury healing results into scar tissue formation. Scar tissue may entrapped the nerve or induce pressure on nerve continuously resulting in to predominant pain symptom. The pain may persist for months or years beyond the apparent healing of any damaged tissues. In this setting, pain signals no longer represent an alarm about ongoing or impending injury; instead the alarm system itself is malfunctioning. Failed back syndrome is a common cause of chronic pain leading to disability and unemployment.
Chronic Non-Cancer Neuropathic Pain :
- Chronic Regional Pain Syndrome Type I (Causalgia): Pain is triggered by a Nerve Injury and may not be associated with actual surrounding soft tissue Damage.
- Chronic Regional Pain Syndrome Type II (Reflex Sympathetic Dystrophy): Pain secondary to nerve injury associated with surrounding soft tissue damage Pain is provoked by pressure or compression of nerves. Pain may be induced by inflamed nerve secondary to Infection.
Causes of Chronic Neuropathic Pain
List Of Diseases Causing Chronic Neuropathic Pain Are As Follows:
- Failed back syndrome: Pain following surgery in the scar tissues.
- Peripheral neuropathy: This is induced by medication, chemotherapy, radiation treatments, and vitamin deficiency.
- Diabetic Neuropathy
- Inflammatory conditions: Joint Pain, Arthritis.
- Pinched Nerve: Scar tissue, disc herniation, disc fragments, Entrapment Neuropathy.
- Complex Regional Pain Syndrome- Amputation: Phantom pain
- Trigeminal Neuralgia.
- Multiple Sclerosis.
- Shingles: Postherpetic Neuralgia.
Causes Of Cancer Neuropathic Pain
Primary Cancer :
- External Organ: Skin, Muscles, Breasts.
- Internal Organs: Esophagus, Stomach, Intestines, Liver, Gallbladder, Kidney, Uterus.
- Metastasis: Spread of cancer to adjoining tissues.
- Local: Near primary cancer.
- Distal: Location distant from primary e.g. Brain, Lungs.
Symptoms And Signs of Chronic Neuropathic Pain
Characteristics Of Non – Cancer Neuropathic Pain:
- Initial Pain: Burning, lancinating, or electric shock qualities.
- Later Pain: Shooting Pain associated with Tingling and Numbness.
- Moving or touching the limb is often intolerable
- Musculoskeletal symptoms: Muscle spasms, joint stiffness, muscles atrophy.
- Flexor tendon contraction
- Edema : Local swelling
- Sweating : increased Abnormally increased sweating,
- Skin temperature : usually hot but sometimes cold
- Skin color : bright red or a reddish violet
- Bones : softening and thinning
- Joint: tender, stiff, restricted or painful movement, restricted mobility, thickening of synovial membrane and joint.
- Hair: rapid hair growth.
- Nail: growth rapid, nails become cracked, brittle, grooved, and spotty.
- Osteoporosis becomes severe and diffuse.
- Emotional stress.
- Allodynia pain with light touch (non painful stimulus), severe amplified response to a stimulus, which is normally just painful.
- Hyperalgesia an exaggerated sense of pain at the site of injury and surrounding tissue disproportionate to the provocativestimulus
- Hyperpathia a painful stimulus induces extreme level of pain unlike allodynia where a non-painful stimulus induces exaggerated pain.
Treatment for Chronic Neuropathic Pain
- Manual Focused Therapy
- Interventional treatment
- Behavioral therapy
1. Medications for Chronic Neuropathic Pain
- NSAIDs: For pain due to tissue inflammation, recommend nonsteroidal antiinflammatory medications.
- Opioids : Have side effects or provide little relief with NSAIDs
- Muscle relaxer: Baclofen, soma, Flexeril.
- Adjuvant pain meds : Lyrica, Neurantin, Elavil, Cymbolta
2. Manual Focused Therapy for Chronic Neuropathic Pain
- chiropractic treatment
- Osteopathic manipulation
- Physical therapy.
3. Interventional Rx for Chronic Neuropathic Pain
- Peripheral nerve blocks with cortisone injections
- Epidural or caudal cortisone injections
- Sympathetic blocks
- Nerve ablation via cryo or radiofrequency techniques.
- Spinal Cord stimulator
- Intrathecal pain pump
4. Surgery for Chronic Neuropathic Pain
- Excision of skin tissue or hardware which is the pain generator.
- Excision of cancerous tissues
- Radiation treatment to shrink tumor mass for release of pressure on nerves.
6. Behavioral Therapy
Opioid Medications for Chronic Neuropathic Pain
- Less robust response to treatment with opioids.
- May respond well to other drugs such as anti-seizure and antidepressant medications with opioids.
- Conservative treatment with medications- Neuropathic pain is a difficult symptom to treat with conservative treatment.
- Conservative treatment includes medication, physical therapy, massage and acupuncture.
Opioid Medications in Neuropathic pain- Interventional Pain Therapy
- Regional pain therapy such as nerve block with corticosteroid may relieve the pain for short period of time. Pain relief could be 2 to 4 month with cortisone injections.
- Cryo, radiofrequency or chemical neuro ablation: May give pain relief for 6 months to 2 years or longer.
- Spinal cord stimulator: Higher success rate and higher percentage of pain relief achieved with advanced pain management includes dorsal column stimulator.
- Intrathecal catheter and electronic pump delivering pin medication intrathecally.
Multidisciplinary Treatment :
- Pharmacist : Calculate and adjust opioid dosage
- Psychiatrist to treat associated nosocomial symptoms e.g. depression or anxiety
- Oncologist to treat cancer with chemotherapy and opioids.
- Radiation oncologist to treat cancer tissue with radiation.
- Physical medicine rehab physician to treat with manual directed treatment.
- Anesthesiologist for interventional treatment and Surgeon.
- In chronic neuropathic pain patient ‘any pain relief’ is rewarding.
Investigations for Chronic Neuropathic Pain
- X- ray: Check osteoporosis, patchy osteoporosis.
- Bone scan: Detects osteoporosis changes early.
- Bone Densitometry: Osteoporosis detected after x-ray as quickly as two weeks.
- Sweat Test: Abnormal sweating can be detected by several tests.
- Non-quantitative Test: color changes of testing agent. E.g. powder.
Quantitative Tests :
- Resting sweat output test- measures sweat quantity.
- Quantitative sudomotor axon reflex test.
- Measures temperature of the symptomatic area Reliable in differentiating neuropathic pain from nociceptive pain.
- Measures altered blood flow in disease area not reliable as sole investigation – similar reading observed in Chronic smoker.
- Skin lotion if used,Recent physical activity, Prior trauma to the region. Vasomotor instability.
- Nerve Conduction Study.
- Diagnostic Sympathetic Blocks.