PAIN

Overview of pain

• Pain is the most common reason people visit their doctor. Pain may be sharp or dull, intermittent or constant, or throbbing or steady.

• Sometimes pain is very difficult to describe. Pain may be felt at a single site or over a large area.

• The intensity of pain can vary from mild to

intolerable.

Acute Versus Chronic Pain

Pain may be acute or chronic. Acute pain begins suddenly and usually does not last long. Chronic pain lasts for weeks or months

Usually, pain is considered chronic if it does one of the following:

Recurs off and on for months or years

Lasts for more than 1 month longer than expected based on the illness or injury

Is associated with a chronic disorder (such as cancer, arthritis, diabetes, or fibromyalgia) or an injury that does not heal

Acute versus Chronic Pain

•When severe, acute pain may cause anxiety, a rapid heart rate, an increased breathing rate, elevated blood pressure, sweating, and dilated pupils.

•Usually, chronic pain does not have these effects, but it may result in other problems, such as depression, disturbed sleep, decreased energy, a poor appetite, weight loss, decreased sex drive, and loss of interest in activities.

Types of Pain

Neurophatic pain

Nociceptive pain

Psychogenic pain

Neurophatic Pain• Neuropathic pain is caused by damage to or

dysfunction of the nerves, spinal cord, or brain.

• Neuropathic pain may be felt as burning or tingling or as hypersensitivity to touch or cold.

• Causes include compression of a nerve (for example, by a tumor, by a ruptured intervertebral disk, or as occurs in carpal tunnel syndrome), nerve damage (for example, as occurs in a metabolic disorder such as diabetes mellitus), and abnormal or disrupted processing of pain signals by the brain and spinal cord.

Nociceptive Pain

• Nociceptive pain is caused by an injury to body tissues.

• The injury may be a cut, bruise, bone fracture, crush injury, burn, or anything that damages tissues. This type of pain is typically aching, sharp, or throbbing. Most pain is nociceptive pain. Pain receptors for tissue injury (nociceptors) are located mostly in the skin or in internal organs.

The pain almost universally experienced after surgery is nociceptive pain. The pain may be constant or intermittent, often worsening when a person moves, coughs, laughs, or breathes deeply or when the dressings over the surgical wound are changed.

Most of the pain due to cancer is nociceptive. When a tumor invades bones and organs, it may cause mild discomfort or severe, unrelenting pain. Some cancer treatments, such as surgery and radiation therapy, can also cause nociceptive pain. Pain relievers (analgesics), including opioids, are usually effective.

Nociceptive Pain

Psychogenic Pain• Psychogenic pain is pain that is mostly

related to psychologic factors.

• When people have persistent pain with evidence of psychologic disturbances and without evidence of a disorder that could account for the pain or its severity, the pain may be described as psychogenic.

• However, psychophysiologic pain is a more accurate term because the pain results from interaction of physical and psychologic factors. Psychogenic pain is far less common than nociceptive or neuropathic pain.

Neuropathic pain

IASP Definitions: Peripheral Neuropathic and Central Neuropathic Pain

12

Neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the nervous system

Peripheral neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the peripheral nervous system

Central neuropathic painPain initiated or caused by a primary

lesion or dysfunction in the central nervous system

Merskey H et al. (Eds) In: Classification of Chronic Pain: Descriptions of Chronic Pain Syndromes and Definitions of Pain Terms. 1994:209-212.

The pain may be spontaneous, stimulus-

evoked, or a combination of both. Its characteristics are often different

from those of other types of pain, such as the nociceptive pain experienced after an injury.

In neuropathic pain the central neurons are sensitised, so that they fire spontaneously, or abnormally.

If this sensitisation persists the pain becomes chronic and is often difficult to treat.

The Inter-Relationship Between Pain, Sleep, and Anxiety / Depression

15Nicholson and Verma. Pain Med. 2004;5 (suppl. 1):S9-S27

Pain

Sleepdisturbances

Anxiety &Depression

Functional impairment

There are considerable overlaps in the pain descriptors between nociceptive and neuropathic pain.

Some patients may have nociceptive and neuropathic pain.

Clues to a neuropathic origin : continuous nature (as opposed to

movement- induced pain) burning shooting qualities.

There are also associated symptoms (derived from irritation to non-noxious afferent neurons) :

The most confusing element is the extension of areas of stimulus-evoked pain beyond the anatomical boundary of the area receiving the stimulus. This occurs because central sensitisation does not respect these boundaries.

ExamplesPeripheral• Postherpetic neuralgia• Trigeminal neuralgia• Diabetic peripheral neuropathy• Postsurgical neuropathy• Posttraumatic neuropathyCentral• Poststroke painCommon descriptors2

• Burning• Tingling• Hypersensitivity to touch or cold

Examples • Pain due to inflammation• Limb pain after a fracture• Joint pain in osteoarthritis• Postoperative visceral pain Common descriptors2

• Aching• Sharp• Throbbing

Examples • Low back pain with

radiculopathy• Cervical

radiculopathy• Cancer pain• Carpal tunnel

syndrome

Mixed PainPain with

neuropathic and nociceptive components

Neuropathic PainPain initiated or caused by a

primary lesion or dysfunction in the nervous system (either peripheral or

central nervous system)1

Nociceptive PainPain caused by injury to

body tissues (musculoskeletal,

cutaneous or visceral)2

CLINICAL PAIN SYNDROME

1. International Association for the Study of Pain. IASP Pain Terminology.2. Raja et al. in Wall PD, Melzack R (Eds). Textbook of pain. 4th Ed. 1999.;11-57

The investigations of neuropathic pain vary according to the suspected cause of each syndrome.

A cause should be sought in each case, and treatment of that cause may contribute to alleviation of symptoms and retard progression of the condition.

For example, irritation caused by a prosthesis may be contributing to a patient's pain following amputation.

Successful Management of Neuropathic Painhas a Positive Impact for The Patient

22

Treatment of underlying conditions and symptoms

Diagnosis

ImprovedQuality of

Sleep

Improved Overall

Quality of Life

Improved Physical

Functioning

Improved Psychological

State

Reduced pain

Neuropathic Pain TreatmentNon-drug treatments can help to control

the patient's pain. A multidisciplinary approach may be required.

Current drug treatments are focused on dampening the neuronal input to consciousness by suppressing axonal function (for example sodium channel blockade) or interfering with neurotransmission (blockade of excitatory and inhibitory neurotransmitters and modulators).

The drugs used to treat neuropathic pain can be conveniently divided into two types:

medications used to treat other conditions but found to be useful in reducing pain from nervous system damage,

analgesics.

Antidepressants

Amitriptyline : The starting dose is low ( 10–12.5 mg at bedtime) and is increased slowly at intervals of a few days to a week. The maximum effective dose is usually 75 mg at night

AnticonvulsantsThere is a long tradition of using

antiepileptic drugs in neuropathic pain.

PhenytoinCarbamazepineValproateLamotrigineTopiramate

AnticonvulsantsNewer drugs :Gabapentin and Pregabalin

Adverse effect :DrowsinessDizzinessAtaxiaDry mouthEdemaWeight gain

AnalgesicsSimple analgesics are often ineffective in

neuropathic pain, but frequently there is a nociceptor component to the patient's pain.

OpioidsOxycodone Morphine

Non Opioid:Tramadol

NSAIDThere is no indication for the use of non-

steroidal anti-inflammatory drugs in patients with neuropathic pain unless there is clear clinical evidence that a nociceptor pain source is contributing to the patient's pain.