Neuropathic Pain Syndromes
CENTRAL POST STROKE PAIN (CPSP)
CPSP develops in 8% of stroke victims. Burning seems to be the most common descriptor of pain, while most patients have more than one kind of pain (continuous pain, sudden spells of pain and pains when touched or moved). The pain seems to be moderate to severe at least in 50% of the stroke victims. It appears immediately after stroke in more than 1/3 of patients, days to 12 months later in half of the patients, 2 years in 9.5% and more than 2 yrs in 4.5%. The motor and sensory abnormalities in CPSP are variable. Examples of sensory abnormalities are hypoesthesia, hyperesthesia, paresthesiae or dysesthesiae. CPSP seems to arise from brain lesions that damage the connections that carry messages from the spine to the brain (spino-thalamo-cortical pathways).
Traditional neuropathic pharmacotherapy and opioids as well as deep brain stimulators in the most severe cases have limited success. Usually the patients require more than one drug in order to obtain some relief.
TRAUMATIC SPINAL CORD INJURY (TSCI)
According to many studies, pain occurs in 40-75% of people with TSCI. It is moderate to severe, often associated with depression and/or anxiety and impairs function and enjoyment of life.
Pain after TSCI can be:
- Neuropathic occurring at the level of the injury (often due to damage of the nerve roots at the site of trauma as in the case above) or below the level of the injury (called central or deafferentation pain);
- Musculoskeletal pain above or below the injury level; and
- Visceral pain (from the bladder or the bowels)
Neuropathic pain can also occur as a consequence of TSCI (for example due to development of a syrinx or cavity within the spinal cord). A recent literature review showed that there is limited or no success with different pharmacological and other treatments. In practice, traditional neuropathic drugs, opioid analgesics, physical modalities, acupuncture, relaxation techniques and rarely surgery are tried, but with limited success.
MULTIPLE SCLEROSIS (MS)
MS is a disease that attacks the brain and spinal cord by causing inflammation and damage to the protective myelin covering of the CNS. In recent studies up to 65% of MS patients have been reported to have pain (usually in more than one site).
- Is directly related to the disease;
- May arise from musculoskeletal reasons (painful muscle contractures, stiff joints, back pain etc); or
- Originates from MS treatments (steroids and ß interferon)
The most common chronic pain syndrome seems to be dysesthetic leg pains, while common acute pain conditions are neuralgias, optic neuritis pain and brief painful tonic spasms.
Pain management in MS is complex as the doctor must take in account multiple symptoms (bladder problems, spasticity, depression, fatigue etc) and many medications the patient takes at the same time. Certain rehabilitation approaches may be helpful (to correct body mechanics or for reconditioning).
Medications for pain have variable and often limited effects (NSAIDS and acetaminophen, antispasticity drugs, anticonvulsants, antidepressants, opioids and oral cannabinoids). A buccal spray containing extracts of natural cannabis has been recently approved by Health Canada to assist in the treatment of neuropathic pain in MS. However, more studies are needed to confirm the clinical benefits that some early research has shown.
Syringomyelia (cavitations within the spinal cord) is rare. It may be "communicating" (associated with "Chiari malformation") or "non-communicating" (running in families, after spinal cord trauma, spinal tumour etc). A survey of the Canadian Syringomyelia Network participants during their 1996 convention found that 97.5% of the responders had pain. In a recent study pain was the only symptom at the beginning of syringomyelia in 59% of the patients and the primary cause of disability in 69% of the sufferers. Most patients had more than one type of pain involving multiple body areas. Pain was rated as moderate in 70% of the patients and severe in 11%. Interestingly, the sensory abnormalities with hypoesthesia to touch, pin prick and cold were covering large areas of the body and only partially matched the areas of pain.
While a surgical procedure called shunting of the syrinx may improve balance and bladder problems, it usually does not improve pain. Traditional neuropathic pharmacotherapy and opioids have variable success.
FAILED BACK SURGERY SYNDROME (FBSS)
The term FBSS refers to patients who have persistent pain and disability after spinal surgery. Despite the high cost and frequency of surgery, the results are poor in 10 to 40% of patients. There are many reasons for failure. Psychological factors include certain personality characteristics and faulty coping mechanisms, anxiety or depression etc. Factors relating to the surgery itself are failure to completely remove the disc or other pathology, excessive surgery, damage already done by a big disc, root injury during surgery and (most common of all) operating on a patient who has nothing that warrants surgery. After the surgery, recurrent disc herniation or "epidural fibrosis" known as scar tissue could be sources of continuous pain. Epidural scar forms 6 weeks to 6 months postoperatively in 10-75% of the patients, but the vast majority do NOT have symptoms.
Epidural steroid injections are widely performed, but their value is questionable. Drugs include NSAIDs, antidepressants, anticonvulsants and opioids. Spinal stimulators and intrathecal opioid pumps may be used in patients resistant to conventional therapy. Therapy should not focus only on medical/surgical management as chronic pain management programs seem to be more effective.
TRAUMATIC BRACHIAL PLEXUS INJURY
More than 80% of patients with avulsion of one or more brachial plexus roots suffer from serious constant, burning or crushing pain often coming in very brief spells (paroxysms) of agonizing intensity and lasting for seconds. Most patients are young men involved in traumatic accidents. Extremes of temperature and emotional stress aggravate the pain, while it is relieved by distraction (when the patient's attention is switched to other things than pain). Two thirds of the patients seem to experience some improvement within 3 years, while in the remaining 1/3 the pain may steadily get worse with age.
Treatments like traditional neuropathic medications (TCAs and antiepileptics), opioids, supportive therapy etc. provide limited relief or no relief at all. The two most helpful interventions at the opposite ends of the technological and medical spectrum include distraction techniques (for example imagery) and DREZ lesions of the avulsed roots (a surgical procedure performed by neurosurgeons).
POST AMPUTATION PAIN
The feeling of a missing limb can be painless (phantom sensation) or painful (phantom pain). Phantom limb pain can follow amputation of any body part including limb, breast, tooth or rectum and occurs within the first week after amputation at least in 50-75% of the patients, but also any time after it. Several PNS and CNS abnormalities may account for phantom limp pain. Recent neuroimaging studies show changes in activity, size and location of brain tructures appearing within hours from the loss of the body part. Unfortunately, the existing studies in the literature do not tell the difference between phantom pain and stump pain (the latter more often caused by focal neuroma, a form of sensitive knot at the site of the cut nerves). Pain is described as squeezing, burning, shooting or aching, often associated with abnormal movements/posture of the phantom.
Treatments are numerous with generally poor results, including non-surgical therapies (TENS, acupuncture, relaxation techniques, neuropathic medications and opioids), while surgical techniques include stump revision with neuroma implantation within deep tissues, DREZ surgery and spinal cord or brain stimulation.
Diabetic polyneuropathy affects primarily the nerves of feet and hands in both insulin and non-insulin dependent diabetes. Single nerves can also be affected either due to lack of blood supply (ischemic mononeuropathy) or because they become vulnerable to compression (an example is a pinched nerve in the wrist that causes carpal tunnel syndrome). The most common forms of painful neuropathy are ischemic mononeuropathy and distal polyneuropathy. In the latter, patients may experience gradual onset of aching, burning and/or shooting pain, numbness and dysesthesiae in their feet and feel out of balance.
While proper sugar control can slow the progression of polyneuropathy, it may do little to control pain. Antiepileptics (particularly gabapentin and pregabalin) and less so TCAs have been shown to work in many people. Opioids may be used as adjuncts in certain cases. A cream containing capsaicin, the ingredient of hot chilli peppers, has been reported in some studies to offer relief but many patients find it intolerable due to the burning it produces. Proper foot care and regular activity are a must.
COMPLEX REGIONAL PAIN SYNDROME (CRPS) (Also known as Reflex Sympathetic Dystrophy/RSD)
CRPS is a complex set of symptoms and signs associated with severe pain. It continues to be the focus of intense research around the world. There have been many attempts to standardize the criteria that one uses to diagnose the syndrome. However, the 1994 IASP criteria proved to diagnose CRPS in a lot more people than they should. A very recent IASP publication (2005) proposed the following clinical criteria:
- Continuing pain out of proportion to any traumatic event;
- At least reporting by the patient of one symptom in 3 of the 4 following categories and observation by the health practitioner of one sign in 2 or more of the following:
- Abnormal sensation (hyperesthesia and/or allodynia)
- Temperature and/or colour changes or asymmetry
- Sweating and/or edema abnormalities, and
- Decreased range of movement and/or motor dysfunction and/or trophic changes.
- No other diagnosis better explains the signs and symptoms.
The cornerstone of treatment is physiotherapy with mobilization. Sympathetic blocks may help, but the role of SNS has been downplayed as large numbers of patients respond to sham blocks.
Traditional neuropathic pharmacotherapy, opioids and spinal stimulators may be of help, while surgical sympathectomy is not advocated due to multiple complications.
TRAUMATIC AND COMPRESSIVE NERVE INJURIES
When a nerve is cut, the surgeons must work quickly to reattach it. When, however, the nerve is injured but not transected, it usually recovers on its own and surgeons will wait for 2-3 months.
Common chronic neuropathies due to trauma or compression in the upper extremities, are carpal tunnel at the wrist and ulnar nerve entrapment at the elbow; in the chest wall, intercostobrachial nerve injury after breast surgery and intercostal nerve damage after cardiac bypass surgery; in the abdominal wall, genitofemoral and ilioinguinal nerve damage; in the perineum, pudendal neuropathy; and in the lower extremities, lateral femoral cutaneous nerve of the thigh entrapment (meralgia paresthetica), sciatic nerve injury (e.g. after hip fractures), tibial nerve compression in the inside part of the ankle, peroneal nerve injury just below the outside of the knee, sural nerve compression behind the knee, or entrapment of small nerves in between the toes (Morton's neuroma).
Treatment includes neuropathic medications, opioids, spinal or peripheral nerve stimulation and occasionally surgery (neurectomy, neuroma implantation within deep tissues etc).
NERVE TUMOURS INCLUDING NEUROMAS
Peripheral nerve tumours are rare. Benign tumours arising spontaneously from the cover of a nerve (nerve sheath) are usually schwannomas and neurofibromas. Other types of nerve tumours are neuromas created by trauma (traumatic neuromas) or compression (Morton's neuroma in between the toes often due to tight shoes). Schwannomas involve most frequently the nerve responsible for our hearing (acoustic neuroma), and surgery to remove such a tumour may produce damage to the patient's hearing. Neurofibromas can occur as isolated nerve tumours or be part of neurofibromatosis, a genetic disease, which occurs in 1/3,000 births.
Patients with neurofibromatosis may have variable presentation: a few pigmented skin spots of no clinical significance or a devastating disease with multiple tumours in many organs which tend to turn into cancer.
Most cases of trigeminal neuralgia (TN) or tic douloureux are of unknown origin. Occasionally, however, TN occurs in multiple sclerosis (MS) or facial trauma. Roughly TN affects 5.7 women and 2.5 men in 100,000 people every year in the USA. TN occurs in spells in the trigeminal nerve territory (one side of the forehead, cheek or jaw) in about 95% of the cases. Pain in both sides of the face may occur years later, particularly in patients with MS. The paroxysms come in clusters and last minutes or seconds followed by brief pain free periods and occur rarely at night. Touching, shaving, washing, air drafts, chewing etc. can generate outbursts of pain. 50% of patients identify a trigger zone and occasionally complain that their nose drips or their eye tears.
Neurological examination is normal but sophisticated testing may show minor sensory loss. The patients may be free of pain for days to months or years.
Carbamazepine (an antiepileptic) seems to be the first line treatment. In case of failure or intolerant side effects, newer antiepileptics (e.g. gabapentin or others) may be helpful. Compression of the trigeminal nerve inside the brain by abnormal arteries or veins can be relieved surgically.
POST-HERPETIC NEURALGIA (PHN)
PHN is the most frequent debilitating complication of Herpes Zoster or Shingles (after reactivation of the dormant VZV virus in the sensory ganglia). In 36.6% of patients older than 60 years and 47.5% of those older than 70, pain lasts more than a year. Patients are at greater risk for PHN as they get older, if they experience intense pain during acute shingles, if the original rash was severe or they had serious emotional stressors at the onset of shingles.
Antiviral therapy reduces severity and duration of shingles and may prevent PHN, but not in all cases. Available treatments shown to work for some patients are topical lidocaine patch 5% (not available in Canada), gabapentin, TCAs, opioids and the recently approved drug in Canada for neuropathic pain (pregabalin). Nerve blocks, cutting nerves or use of spinal stimulators have unproven effectiveness.
A recently published study of 38,000 adults older than 60 years of age tested a special vaccine (Oka/Merck VZV vaccine) and showed that it works quite well in reducing the severity of shingles and the occurrence of PHN. The vaccine is now available in the USA and expected to be available in Canada too, soon.
PAIN AFTER BREAST SURGERY
A quarter or more of women who have breast surgery report pain a year later. Specifically, pain after breast surgery for cancer is not a simple syndrome as several entities have been described: phantom breast pain, nerve injury pain (as in the case reported here), brachial plexus neuropathy due to infiltration by cancer or due to scarring after radiotherapy, cervical radiculopathy, shoulder inflammation etc. Breast pain can also occur after non-cancer surgeries as in the case of breast implants or breast reduction. It is not easy to separate and understand the different mechanisms of pain after breast surgery and the pain is not well recognized and managed by physicians.
Traditional treatments for neuropathic pain (pharmacological and local) as well as non-opioid and opioid analgesics have variable success.
CHEST PAIN AFTER CARDIAC BYPASS SURGERY
A specific syndrome after cardiac bypass surgery with the use of internal mammary artery was first described in 1989. Patients present with burning and shooting chest pain across a specific chest wall area as shown in the case above. Touch and pinprick hypersensitivity usually go away within 1-1.5 year in most patients who become pain free. In one study intercostal nerve damage was detected in 73% of the study subjects, 15% of which had persistent pain 5-28 months after surgery. Patients are often submitted to multiple cardiac investigations as the pain is not well understood by their physicians.
Once diagnosed, available treatments include antiepileptics and TCAs (the latter should be used carefully in patients with cardiac arrhythmias), local modalities like TENS (contraindicated in patients with pacemakers) or deep heat (laser or ultrasound), analgesics (non-opioids and/or opioids) and supportive therapy. Pain severity ranges from negligible to serious. Chest pain after bypass surgery may be due to other causes as well (scar hyperalgesia, inflammation of the joint between the ribs and the chest bone called costochondritis or be "referred" from other structures like the esophagus or "food pipe").