Chronic pain

Editor-in-Chief: Steven D. Feinberg, M.D. Adjunct Clinical Professor, Stanford University School of Medicine, Board Certified, Physical Medicine and Rehabilitation, Board Certified, Electrodiagnostic Medicine, Board Certified, Pain Medicine, Qualified Medical Evaluator (QME)

Associate Editor-in-Chief:

Overview
Chronic pain was originally defined as pain that has lasted 6 months or longer. More recently it has been defined as pain that persists longer than the temporal course of natural healing, associated with a particular type of injury or disease process.

The International Association for the Study of Pain defines pain as "an unpleasant sensory and emotional experience associated with actual or potential tissue damage, or described in terms of such damage." It is important to note that pain is subjective in nature and is defined by the person experiencing it, and the medical community's understanding of chronic pain now includes the impact that the mind has in processing and interpreting pain signals.

As a summary;


 * Chronic pain is defined as pain that continues beyond the recognized time for the body to heal (usually 4-6 weeks)
 * Historically, chronic pain is underdiagnosed, and therefore undertreated
 * Chronic pain becomes a disease state itself without a physiologic role
 * Depending upon the distribution of symptoms, the pain can be categorized as regional or diffuse
 * High rates of psychiatric co-morbidities exist with these conditions

Functional Anatomy
The anatomy of the nociceptive system can be grossly divided into the peripheral and central nervous system. The peripheral nervous system consists of small myelinated and unmyelinated nerve fibers. These nerve fibers converge into a region of the spinal cord referred to as the dorsal horn. The dorsal horn is the first relay station in pain signal transmission. The next element of pain transmission includes nerve fibers that then travel to the thalamus. From the thalamus the next order of neurons ascend to the limbic system and sensory cortex. This accounts for the affective elements and discriminative of pain respectively.

Nociception
The experience of pain biologically is referred to as nociception. Nociception occurs in any tissue or organ in which pain signals arise secondary to a disease process or trauma. The nociception can also occur if there is dysfunction or damage to nerves themselves.

The Pathophysiology of Chronic Pain
Under persistent activation nociceptive transmission to the dorsal horn may induce a wind up phenomenon. This induces pathological changes that lower the threshold for pain signals to be transmitted. In addition, it may generate nonnociceptive nerve fibers to respond to pain signals. Nonnociceptive nerve fibers may also be able to generate and transmit pain signals. In chronic pain this process is difficult to reverse or eradicate once established.

Classification
Nociception (pain) may arise from injury or disease to visceral, somatic and neural structures in the body. More broadly pain is described as malignant or non-malignant in origin.

Diagnoses
Pain may be a response to injury or any number of disease states that provoke nociception. Advances in imaging studies and electrophysiological studies allow us to gain a deeper insight into the characteristics and properties associated with the phenomenon of chronic pain.

History and Symptoms

 * Detailed surgical and medical history
 * Previous treatments/medications
 * The effects the symptoms have on the patient's life
 * Symptom history should include:
 * Location
 * Onset
 * Character
 * Intensity
 * Duration
 * Radiation
 * Associate symptoms
 * Alleviating factors
 * Aggravating factors

Physical Examination

 * Thorough physical examination with special attention paid the areas where the symptoms are present (both soft-tissue regions and joints)
 * Comprehensive mental status examination:
 * Mood of patient
 * Affect
 * Insight
 * Ideation
 * Individual system evaluation

Laboratory Findings

 * The labs may vary depending upon the location of the symptoms, as well as the organs involved.
 * Some of which may include:
 * Complete blood count (CBC)
 * Calcium
 * Glucose
 * Blood urea nitrogen (BUN)/creatinine
 * C-reactive protein (CRP if inflammatory disease is suspected)
 * Erythrocyte sedimentation rate (ESR again, if inflammatory disease is suspected)
 * Creatinine phosphokinase (CPK for myopathies)

Electrolyte and Biomarker Studies

 * Electrolytes

Other Imaging Findings

 * Similar to lab studies, imaging is symptom specific and should be condition-specific
 * Electromyogram (EMG) may be considered depending upon the presentation of symptoms

Chronic Pain Syndrome
Chronic pain may generate other adversities including affective symptoms of depression and anxiety. It may also contribute to decreased physical activity given the apprehension of exacerbating pain. Conversely it may itself have psychosomatic or psychogenic component to its cause.

Cancer Pain

 * Bony pain secondary to metastasis
 * Postradiation mucositis or neuritis
 * Visceral pain secondary to mass effects

Headache

 * Cervical radiculopathy
 * Cluster headache
 * Migraine headache
 * Temporomandibular Joint Syndrome
 * Tension headache

Low Back Pain

 * Facet Syndrome
 * Lumbar radiculopathy
 * Myofascial pain
 * Spinal Stenosis

Musculoskeletal

 * Ankylosing Spondylitis
 * Bilateral soft tissue Rheumatism
 * Dermatomyositis
 * Eosinophilia myalgia syndrome
 * Fibromyalgia
 * Myofascial pain syndrome
 * Polymyalgia
 * Polymyositis
 * Psychogenic rheumatism
 * Reiter's Syndrome
 * Repetitive strain syndromes
 * Rheumatoid Arthritis
 * Silicone implants
 * Sjogren's Syndrome
 * Soft tissue injury
 * Vasculitis

Neuropathic

 * Cervical radiculopathy
 * Diabetic neuropathy
 * Phantom limb
 * Post-herpetic neuralgia
 * Postoperative thoracotomy
 * Reflex sympathetic dystrophy

Pelvic/Abdominal

 * Endometriosis
 * Fibroids
 * Interstitial cystitis
 * Irritable Bowel Syndrome

Psychiatric

 * Anxiety
 * Depression
 * Emotional, physical, and/or sexual abuse
 * Malingering
 * Somatization

Miscellaneous

 * Chronic Fatigue Syndrome
 * Entrapment neuropathy
 * Hypermobility
 * Hyperthyroidism
 * Hypophosphatemia
 * Hypothyroidism
 * Metabolic bone disease
 * Multiple Sclerosis
 * Osteomalacia
 * Overuse syndromes
 * Paraneoplastic syndrome
 * Postviral arthralgia, myalgia

Complete Differential Diagnosis of the causes of Chronic pain
(In alphabetical order)


 * Achilles tendinitis
 * Acute Chest Syndrome
 * Acute intermittent porphyria
 * Acute myeloid leukemia
 * Alcoholic Hepatitis
 * Alexithymia
 * Amyotrophic lateral sclerosis
 * Anal fistula
 * Angina pectoris
 * Angioedema
 * Ankylosing Spondylitis
 * Anxiety
 * Aphthous ulcer
 * Arachnoiditis
 * Ascaris infection
 * Ascending cholangitis
 * Atheroembolic disease
 * Autoimmune Hepatitis
 * Autoimmune pancreatitis
 * Baker's cyst
 * Barrett's esophagus
 * Behcet's disease
 * Benign fasciculation syndrome
 * Beriberi
 * Bilateral soft tissue Rheumatism
 * Bony pain secondary to metastasis
 * Budd-Chiari syndrome
 * Buerger's disease
 * Cancer Pain
 * Caplan's Syndrome
 * Carpal tunnel syndrome
 * Celiac disease
 * Cellulitis
 * Cerebellar Infarction
 * Cervical radiculopathy
 * Chlamydia infection
 * Cholangiocarcinoma
 * Cholangitis
 * Cholesterol Emboli Syndrome
 * Cholesterol pericarditis
 * Chondromalacia patellae
 * Chronic bronchitis
 * Chronic Fatigue Syndrome
 * Chronic functional abdominal pain
 * Chronic inflammatory demyelinating polyneuropathy
 * Chronic pelvic pain
 * Chronic Stable Angina
 * Chronic wound
 * Churg-Strauss syndrome
 * Cirrhosis
 * Cluster headache
 * Colorectal cancer
 * Common variable immunodeficiency
 * Complex regional pain syndrome
 * Constrictive pericarditis
 * Conversion disorder
 * Crohn's disease
 * Cystic fibrosis
 * Deep vein thrombosis
 * Degenerative disc disease
 * Depression
 * DeQuervain's syndrome
 * Dermatomyositis
 * Desmoplastic small round cell tumor
 * Diabetic neuropathy
 * Dientamoebiasis
 * Dilated cardiomyopathy
 * Endometrial cancer
 * Endometriosis
 * Entrapment neuropathy
 * Eosinophilia-myalgia syndrome
 * Epididymitis
 * Erythromelagia
 * Esophageal cancer
 * Exostosis
 * Facet Syndrome
 * Familial dysautonomia
 * Farber disease
 * Fibroids
 * Fibromyalgia
 * Frozen Shoulder
 * Fructose malabsorption
 * Functional bowel disorder
 * Fundic gland polyposis
 * Gallbladder cancer
 * Gallstone Disease
 * Gastroesophageal reflux disease
 * Gaucher's disease
 * Gout
 * Graft-versus-host disease
 * Guillain-Barre syndrome
 * Heberden's node
 * Hemorrhoids
 * Henoch-Schonlein purpura


 * Hurler's Syndrome
 * Hypermobility
 * Hyperthyroidism
 * Hypophosphatemia
 * Hypothyroidism
 * Interstitial cystitis
 * Interstitial nephritis
 * Intestinal pseudoobstruction
 * Irritable bowel syndrome
 * Ischemic colitis
 * Juvenile idiopathic arthritis
 * Keratoconjunctivitis sicca
 * Lead poisoning
 * Leukemia
 * Lumbar radiculopathy
 * Lung abscess
 * Lung cancer
 * Lymphangiomatosis
 * Malignant Mesothelioma
 * Metabolic bone disease
 * Migraine
 * Multiple myeloma
 * Multiple Sclerosis
 * Myalgic encephalomyelitis
 * Myofascial pain syndrome
 * Myotonic dystrophy
 * Nasopharyngeal carcinoma
 * Neurofibromatosis type I
 * Neuropathic
 * Obstructive uropathy
 * Opioid-induced hyperalgesia
 * Orchialgia
 * Osteoarthritis
 * Osteochondroma
 * Osteomalacia
 * Otitis media
 * Paget's Disease
 * Pancreatic cancer
 * Paraneoplastic syndrome
 * Pelvic inflammatory disease
 * Pelvic myoneuropathy
 * Peptic ulcer
 * Periodic fever syndrome
 * Peripheral artery occlusive disease
 * Phantom limb
 * Pilonidal cyst
 * Plantar fasciitis
 * Plummer-Vinson syndrome
 * Poliomyelitis
 * Polycystic ovary syndrome
 * Polymyalgia
 * Polymyalgia Rheumatica
 * Polymyositis
 * Post-herpetic neuralgia
 * Post-thrombotic syndrome
 * Psychiatric
 * Psychogenic rheumatism
 * Pudendal nerve entrapment
 * Pyelonephritis
 * Pyoderma gangrenosum
 * Raynaud's phenomenon
 * Reactive arthritis
 * Renal osteodystrophy
 * Repetitive strain syndromes
 * Rheumatoid arthritis
 * Sacrococcygeal teratoma
 * Sarcoidosis
 * Schwannomatosis
 * Sciatica
 * Secondary hyperparathyroidism
 * Short bowel syndrome
 * Sickle-cell disease
 * Sinusitis
 * Sjogren's Syndrome
 * Soft tissue injury
 * Somatization
 * Spinal disc herniation
 * Spinal Stenosis
 * Spondylolisthesis
 * Synovial osteochondromatosis
 * Syringomyelia
 * Systemic lupus erythematosus
 * Temporomandibular Joint Syndrome
 * Tendinitis
 * Tennis elbow
 * Tension headache
 * Tolosa-Hunt syndrome
 * Ulcerative colitis
 * Ulcers
 * Varicose veins
 * Vasculitis
 * Vertebral subluxation
 * Viral Hepatitis
 * Visceral pain secondary to mass effects

Complete Differential Diagnosis of the Causes of Chronic pain
(By organ system)

Treatment

 * Occupational and physical therapy is helpful for most conditions associated with chronic pain
 * Psychiatric evaluations (and therefore treatment) may be required for patients with co-morbidities and psychiatric conditions
 * If necessary, refer patient to a pain specialist

It is rare to completely achieve absolute and sustained relief of pain. Thus, the clinical goal is pain management. Pain management is often multidisciplinary in nature. A recent journal article by Gatchell and Okifuji recognizes the importance of comprehensive pain programs(CPPs) in the management of chronic pain. They summarize their findings as follows: "CPPs offer the most efficacious and cost-effective treatment for persons with chronic pain, relative to a host of widely used conventional medical treatment."

Pharmacotherapies

 * For inflammatory diseases, nonsteriodal anti-inflammatory drug (NSAIDs) are often used
 * For patients with fibromyalgia, selective serotonin reuptake inhibitors (SSRIs) are indicated
 * For patients with neuropathic pain, anticonvulsants and tricyclic antidepressants are useful
 * Narcotics are used for extreme cases, when conservative measures have otherwise failed (risk of dependence is great, and use is therefore a last resort)
 * Tramadol serves as a bridge between the two extremes of treatment (NSAIDs and narcotics)
 * Pain medications may be delivered in the spine for patients with reflex sympathetic dystrophy and radicular pain

Opioids
Opioid medications provide short, intermediate and long acting analgesia depending upon the specific properties of the medication and whether it is formulated as an extended release drug. Opioid medications may be administered orally, by injection, via nasal mucosa or oral mucosa, rectal, transdermal, intravenously, epidurally and intrathecally. In chronic pain conditions that are opioid responsive a combination of a long acting or extended release medication is often prescribed in conjunction with a shorter acting medication for break through pain (exacerbations). Although opioids are strong analgesics, they do not provide complete analgesia regardless of whether the pain is acute or chronic in origin. Opioids are efficacious analgesics in chronic malignant pain and modestly effective nonmalignant pain management. However, there are variable associated adverse effects, especially during the commencement or change in dosing and administration. When opioids are used for prolonged periods drug tolerance, chemical dependency and (rarely) addiction may occur. Chemical dependency is ubiquitous among opioid therapy after continuous administration; however, drug tolerance is not well studied in patients on long term opioid therapy. Addiction rarely occurs as a result of opioid prescription, but they are abused by some individuals, which can cause concern to health care providers. Diversion of opioid medications is another concern for health care providers.

Non-steroidal anti-inflammatory drugs
The other major group of analgesics are Non-steroidal anti-inflammatory drugs (NSAID). This class of medications includes acetaminophen which may be administered as a single medication or in combination with other analgesics. The alternatively prescribed NSAIDs such as ketoprofen and piroxicam, have limited benefit in chronic pain disorders and with long term use is associated with significant adverse effects. The use of selective NSAIDs designated as selective COX-2 inhibitors have significant cardiovascular and cerebrovascular risks which have limited their utilization.

Antidepressants and Antiepileptic drugs
Some antidepressant and antiepileptic drugs are used in chronic pain management and act primarily within the pain pathways of the central nervous system, though peripheral mechanisms have been attributed as well. These mechanisms vary and in general are more effective in neuropathic pain disorders as well as complex regional pain syndrome. Drugs such as Gabapentin have been widely prescribed for the off-label use of pain control. The list of side effects for these classes of drugs are typically much longer than opiate or NSAID treatments for chronic pain, and many antiepileptics cannot be suddenly stopped without the risk of seizure.

Interventional therapy
Injections, Neuromodulation and Neuroablative Therapy may be used to target either the tissue structures and organ/systems responsible for persistent nociception or the nerves conveying nociception from the structures implicated as the source of chronic pain.

Rehabilitation
As alluded to earlier there are other modalities used in the treatment of chronic pain. These include: physical modalities such as thermal agents and electrotherapy. Complementary and alternative medicine, therapeutic exercise and behavioral therapy are also utilized autonomously or in tandem with interventional techniques and conventional pharmacotherapy. This is most often structured in a multidisciplinary or interdisciplinary program.

Controversy
Pain.com UN-INCB

Chronic pain patients are often misdiagnosed. Patients are often ignored, and their pain dismissed as imaginary. Patients, particularly the ones prescribed opioids, are often labeled as drug addicts. Furthermore, chronic pain patients in the United States and other countries, continue to encounter problems caused by their governments' war on illegal drugs (examples include but are not limited to: red tape in applying for/renewal of special prescription pads; government-mandated limits and excessive regulations for hospitals and drugstores; etc.).