Pain is an unpleasant and uncomfortable sensation caused by injury or disease.
It occurs due to the activation of the nervous system and is mainly associated with injury or the threat of injury.
It is actually a warning mechanism intended to protect a living being by directing it to withdraw from harmful stimuli. Sometimes the pain may persist even after the stimulus has been removed or in the absence of any tissue damage or disease.
Pain is not a disease; rather a symptom of an underlying disease.
The word pain comes from the Latin word “poena” which means punishment since it was considered a punishment from Gods.
Different people respond to pain differently. Some people can tolerate high degree of pain, while others have a low tolerance. Hence, pain is a highly subjective feeling.
Pain is a very frequent complaint by the patients and is a common cause of a visit to the physician or pain specialists.
Mechanisms of Pain
The process of the perception of pain is called nociception. There are many mechanisms involved in nociception.
Nociception involves a complex interaction of the peripheral and central nervous systems. It also involves certain chemical processes such as through the release of prostaglandins.
Nociceptive pain is caused by the stimulation of sensory nerve fibers. These nerve fibers respond to stimuli which are perceived as harmful by specialized structures called nociceptors (pain receptor). Nociceptors are classified according to the mode of stimulation. They may be thermal (responding to heat or cold), mechanical (responding to mechanical forces like crushing, tearing, etc.) or chemical (responding to chemicals such as those released by the body during inflammation). Some nociceptors respond to more than one of these stimuli and are hence designated polymodal.
These receptors generate an electrical impulse that travels to the spinal cord. A complex interplay between neurotransmitters is responsible for the transmission of nerve impulses from one cell to another.
The spinal cord acts as a relay center and can either block, modify, or enhance the signal before forwarding the signal to the brain.
Psychogenic pain transmission is linked to the emotional centers in the brain. Feelings like anger and anxiety increase pain perception while positive feelings like happiness tend to decrease it.
Classification of Pain
Acute and Chronic
Acute pain is of recent onset. It occurs suddenly and usually gets over soon though sometimes it can turn into chronic pain. For example, ankle sprain will cause acute pain.
A pain that continues for a longer period of time (three months or longer), or occurs frequently for months is termed as chronic. Back pain or arthritis are examples of chronic pain.
Localized or Generalised
Localized pain affects a specific area of the body.
Generalized pain affects the whole body. An example is the generalized body aches associated with viral fevers.
Nociceptive, Neuropathic, or Psychogenic Pain
It is the pain caused by the activation of pain receptors (nociceptors) present on the skin, external organs as well as the internal organs of the body. Nociceptive pain is further classified according to the site of origin.
Visceral pain originates from injury to the visceral organs like gallbladder, intestine, lungs, liver, etc. or the surrounding tissues that support them. The pain is poorly localized and difficult to locate. It may also be felt as cramping or deep stabbing pain and may be associated with nausea and vomiting.
Read more about Nausea-Causes, Investigations, Home Remedies and Treatment
Deep somatic pain originates from nociceptors present in ligaments, tendons, bones, blood vessels, and muscles. It is dull, aching, and poorly-localized.
Superficial somatic pain originates from the nociceptors present in the skin or other superficial tissue. It is usually sharp and clearly located. Examples include pain due to skin wounds and minor burns.
It is caused by disease affecting a part of the nervous system. Depending upon the part affected, it may be classified as peripheral, central, or mixed neuropathic pain.
This type of pain continues even after the injury has healed.
It can occur due to trauma or diseases like diabetes. Diabetic neuropathy and complex regional pain syndromes are a few examples.
Peripheral neuropathic pain as seen in diabetes is described as burning, tingling, or pins and needles sensation.
This pain is caused or prolonged by emotional factors. Most patients who have chronic pain have some degree of psychological problems like anxiety or depression.
Hence all patients with chronic painful conditions should be evaluated for psychological factors, and psychological treatments should form an important aspect of pain therapy.
It is not possible to measure pain. Pain is a subjective feeling and difficult to quantify. How an individual responds to pain depends on a variety of factors including social, cultural, psychological, and genetic factors. Hence there is a wide variation in pain tolerance among humans.
In spite of medical advances, there is no test to measure the intensity of pain, no imaging device which can show pain and no equipment which can localize pain.
Functional MRI [fMRI] of the brain is being used to measure pain, and it shows a good correlation with self-reported pain.
The characteristics of pain as described by the patient e.g. type, duration, location, whether sharp or dull, constant or intermittent, burning or aching usually provide valuable clues to assess the cause of pain. Once the cause is determined, appropriate treatment can be started.
The investigations required in a patient presenting with pain would depend on the presentation, site of the pain, and associated symptoms.
Appropriate lab investigations or imaging techniques may be carried out based on the above-mentioned features. For example, a patient presenting with upper abdominal pain may require liver function tests, pancreatic tests, and imaging procedures like ultrasound, CT scan or MRI, Other investigations like X-rays, electromyography (EMG), nerve conduction studies, evoked potential (EP) studies, etc may be carried out when deemed appropriate. Discography may be done to locate painful discs.
Psychological evaluation forms an important component of the investigations. Substance abuse should also be evaluated.
Treatment would depend on the underlying cause. However, the immediate aim of treatment, in all cases is to reduce pain and associated discomfort.
Treatment of acute pain includes:
- Rest to the affected part
- Application of heat or ice
- Nonsteroidal anti-inflammatory drugs- aspirin, ibuprofen, naproxen, acetaminophen, etc
- Opioid analgesics
- Anesthetic agents in a few selected cases
Treatment of chronic pain is more complex. It may involve more than one medical specialty, precautions and lifestyle changes on the part of the patient.
Patients who don’t respond to above-mentioned treatments may be offered a secondary line of treatment including steroid injections, anticonvulsants, nerve blocks, biofeedback, and behavioral therapy
Medicines Used for Pain Relief
This group includes
- Nonsteroidal anti-inflammatory drugs like aspirin, acetaminophen, and ibuprofen, etc. They act at the level of peripheral pain receptors. They are effective for minor acute pains, such as headaches, backaches, body aches associated with viral fevers, light sprains, etc. Most of these are available as over the counter drugs. However, it is not advisable to take these medicines for a long period continuously without consulting your doctor.
Read more about Analgesics or Drugs used for Pain Relief
- Opioid drugs like buprenorphine, tramadol. They act at the central nervous system to decrease the perception of painful stimuli. These drugs are available only with a prescription. They are prescribed for more extreme acute pains, such as pain from surgery, burns, cancer, or bone fractures. Morphine is used for severe pain associated with cancer.They are highly addictive and can cause withdrawal symptoms. Also, they tend to lose effectiveness after some time and require higher doses to be effective.
Steroids are extremely potent analgesics and anti-inflammatory agents. Intralesional injection of steroids is a very effective method to provide pain relief in musculoskeletal disorders. However, they have to be used very cautiously as their long term and unsupervised use can result in serious side-effects.
Read more about Side Effects of Corticosteroid Therapy
Carbamazepine is used to treat a number of painful conditions, including trigeminal neuralgia. Drugs like gabapentin or pregabalin are used to treat neural pains.
Antidepressants or anti-anxiety drugs may be used along with analgesics in cases that have a strong psychological component.
Heat or cold therapy
Heat therapy improves circulation and blood flow to a particular area. It helps by relaxing muscles and soothing the stiff joints.
Cold therapy reduces blood flow to a particular area thereby reducing inflammation and swelling that causes pain. It also helps to numb sharp pain.
Local application of irritants like capsaicin increase the blood flow to the skin. This provides warmth and helps to relieve pain.
Sumatriptan, naratriptan, and zolmitriptan are the drugs used specifically for migraine headaches.
Biofeedback is a technique that a person can use to learn to control some of the body’s functions. In this technique, the patient is connected to electrical sensors that provide information about his/her body.
This feedback helps a person to become aware of; and make changes in his/her body functions, such as relaxing certain muscles, to achieve pain relief. It allows a person to change the body’s responses to pain by using relaxation and other techniques.
It is an effective treatment for unrelenting back pains and headaches.
Cognitive Behavioral Therapy
Many causes of pain involve a cognitive element. The patient can be made to learn coping skills and relaxation methods to cope with pain.
Cognitive-behavioral therapy is a type of psychotherapy that helps patients to engage in an active coping process so that they can change their misplaced thoughts and behaviors that usually aggravate the feelings of pain.
This method is helpful in postoperative pain, cancer pain, or pain associated with childbirth.
Electrical stimulation can be given by various methods and each requires specialized equipment and trained personnel.
Transcutaneous electrical nerve stimulation or TENS involves placing small electrodes that conduct electricity, on the skin over the painful part of the body. Tiny electrical impulses are passed through these electrodes to the painful area of the body. These impulses are delivered through the skin to nerve fibers which cause numbness or contractions in the muscles resulting in temporary pain relief.
Peripheral Nerve Stimulation
Electrodes are placed surgically next to one of the peripheral nerves. The electrode delivers rapid electrical pulses that are felt like mild tingles. The patient can deliver an electrical current by turning the device on and off and adjusting the stimulation as required.
Spinal Cord Stimulation
Electrodes are surgically inserted within the epidural space of the spinal cord. The patient is able to deliver a pulse of electricity to the spinal cord by using this device.
Deep brain stimulation
Surgical stimulation of the brain, usually the thalamus is used for a limited number of conditions, like severe pain, central pain syndrome, cancer pain, phantom limb pain, or other severe neuropathic pains.
A group of nerves called a plexus or ganglion, (that is causing pain to a specific organ or body part) can be blocked by injecting a nerve-numbing medicine into it. This procedure is known as a nerve block. It causes an interruption in the relay of pain messages between specific areas of the body and the brain.
Neurectomy, trigeminal rhizotomy, and sympathectomy are few examples.
Light to moderate exercises such as walking, jogging or swimming can improve the muscle tone, strengthen the bones, reduce stress, and result in the overall well-being of the patient. These exercises should be done keeping in mind the patient’s overall health and fitness. In no case should the patients try to perform activities beyond their abilities.
Treatments like acupressure, yoga, music, meditation, or other relaxation techniques can prove useful in certain cases.
Read more about Complementary and Alternative Medicine Therapy
RICE therapy stands for rest, ice, compression, and elevation. It is recommended for temporary muscle or joint conditions, such as sprains or strains or other acute injuries.
Surgery is usually the last resort in a few painful conditions. However, it can’t be performed in all kinds of pain.
Surgical treatments that may provide relief include discectomy (removal of an intervertebral disc), joint fusion, ingrown toenail, appendicectomy (removal of the appendix), cholecystectomy ( removal of gall bladder), etc.