What is Pain & what causes it ?

The sensation of pain is triggered by the nervous system, usually in response to an injury or illness. The pain sensation hurts, causing discomfort, distress and perhaps agony, depending on its severity.

Pain can be felt in a variety of forms; it can be dull and constant, or short and sharp. Pain may be experienced in one area of the body, such as the back or abdomen, or it can be felt all over, like when your muscles ache during the flu. Pain can be very useful for helping to diagnose a problem. Without pain, trauma may occur without someone even realising it. Alternatively, a medical condition may remain hidden without the associated pain to help identify it. Once the instigating injury or illness has been treated, the pain will usually subside. In these instances, the pain can be classified as being acute.

However, sometimes pain can continue for weeks, months or even years. This is known as chronic pain. Chronic pain can be the result of a long-term condition, such as arthritis or cancer. In other cases, the cause can remain unknown. The most common types of pain include:

  • Back pain – most cases of back pain aren’t caused by anything too serious. In most cases, back pain is caused by minor sprains or injuries. These injuries can be incurred by bending or twisting awkwardly, lifting heavy objects, overstretching, slouching or hunching, and overusing muscles. Some cases of back pain can be the result of a more serious medical condition, such as sciatica, arthritis or a slipped or prolapsed disc. On rare occasions, back pain can be the sign of something more serious, such as a spinal fracture or cancer.
  • Headache – headaches can be divided into two categoriesprimary and secondary. Primary headaches are, in most cases, caused by a dysfunction or an over activity in the pain- sensitive structures in the head. Examples of primary headaches include; migraine, tension headache and cluster headaches. Secondary headaches are a symptom of another condition that stimulates the pain-sensitive nerves in the head. An example of a secondary headache is an alcohol-induced hangover.
  • Joint pain – is the result of damage to the joints, either through disease or injury. A variety of conditions can lead to joint pain, including; osteoarthritis, rheumatoid arthritis, gout, bursitis, sprains, strains and other injuries.
  • Period pain – is the result of muscular contractions of the womb. These contractions constantly pass through the womb, however, they are usually so mild that they pass unnoticed. During menstruation, these contractions can become more vigorous. This is to encourage the wombs lining to shed away as part of the monthly cycle. These more intense contractions can compress the blood vessels in the womb, temporarily cutting off the blood supply. Without blood, the tissues in the womb become deprived of oxygen, which causes them to release chemicals that trigger pain in the body.
  • Muscular pain – also known as myalgia, is often the result of too much stress, tension, or physical activity. However, in some cases, myalgia can be related to a medical condition, such as; viral or bacterial infections, fibromyalgia, thyroid problems, hypokalemia (low potassium), autoimmune disorders, and certain medicines, such as ACE inhibitors.
  • Dental pain – toothache is usually the result of the tooths innermost layer becoming inflamed. This layer is known as the dental pulp and is made up of sensitive nerves and blood vessels. The dental pulp can become inflamed as a result of; tooth decay, receding gums, a cracked tooth, loose or broken fillings, and a periapical abscess. Other conditions that can cause dental pain, without the dental pulp being affected, include; sore and swollen gums, sinusitis, ulcers, periodontal abscess, and injury to the temporomandibular joint, which connects the jaw to the skull. Babies can always experience dental pain when their teeth begin to develop. This is called teething.

Pain can be further classified as being; nociceptive, non-nociceptive, somatic, neuropathic, sympathetic, visceral, and referred.

Nociceptive pain occurs when specific pain receptors are stimulated. These receptors sense vibrations, temperature, inflammation, stretching and the chemicals released by damaged cells.

Non-nociceptive pain isn’t caused by specific pain receptors. Instead, it is a response to a nerve(s) becoming injured or unstable, causing its signalling system to become confused. The brain (central nervous system) interprets these abnormal signals as pain.

Somatic pain is a type of nociceptive pain that is experienced on the skin, or in the muscles, joints, ligaments and bones. Somatic pain tends to be sharp and localised at the cause.

Neuropathic pain is a type of non-nociceptive pain. It occurs inside the nervous system itself and is often referred to as a trapped or pinched nerve. This type of pain originates from the peripheral or central nervous system. Causes of neuropathic pain include; nerve degeneration, nerve inflammation, pressure on the nerves or nerve infection.

Sympathetic pain (non-nociceptive) occurs in the sympathetic nervous system. This system controls blood flow, perspiration and the speed at which the peripheral nervous system works. Sympathetic pain usually occurs after bone fractures or soft tissue damage. As with neuropathic pain, sympathetic pain is the result of a nerve becoming injured or unstable, causing it to send abnormal signals to the brain, which then interprets them as pain.

Visceral pain is a type of nociceptive pain. It is usually experienced in the internal organs and main body cavities, such as the thorax, abdomen and pelvis. Visceral pain is harder to localise compared with somatic pain. The sensation will usually resemble a deep ache or cramping.

Visceral pain commonly refers to some type of back pain: Upper back = thoracicmid-back = abdominal, and lower back = pelvic.

Referred pain is sometimes called reflective pain. This form of pain is experienced next to, or at a distance from the origin of the injury. For example, a person suffering a heart attack may feel pain around the shoulders, back or neck, instead of the chest. The origin and causes of referred pain are still unknown.

If the pain is being caused by an underlying disorder, treating said disorder will also relieve the associated pain. For example, if suffering from a bacterial infection, taking the appropriate course of antibiotics should clear up the infection, which should result in the elimination of the associated pain. If the pain is moderate to severe, it may also be necessary to use analgesics (painkillers), until the underlying cause has been treated.

Analgesics are effective at relieving nociceptive pain but aren’t effective at combating neuropathic pain.

Opioid Analgesics

If suffering from a mild headache or a muscle strain, an over-the-counter pain reliever will usually be enough to ease the pain. However, if the pain is more severe, the doctor may recommend something a lot stronger, such as an opioid analgesic.

Opioid analgesics are the strongest painkillers, which are only available with a valid prescription. They are commonly used after surgery, for broken bones, burns, cancer, and under various other circumstances where the pain is likely to be severe. Opioid analgesics work by binding to the opioid receptors in the brain and spinal cord. This causes a reduction in the pain messages being sent to the brain, thus reducing the feelings of pain. An opioid will usually be administered in gradually increasing dosages. The aim of this method of administration is to achieve the ideal dose, which is when the pain is sufficiently relieved, whilst the side-effects remain tolerable. By taking too high a dose, the side-effects can become too much for the sufferer. Opioid dosages are generally much lower for infants and the elderly.

The most common side-effects that opioid analgesics produced include;

  • Nausea/vomiting
  • Drowsiness
  • Constipation
  • Itching

Usually, these side-effects lessen with time. Opioid analgesics should always be taken with great care, as taking too much can be dangerous. Opioids can also cause addiction – patients who use opioids frequently over long periods, can find themselves dependent on them. For these patients, if treatment were suddenly stopped, they would suffer withdrawal symptoms, which makes it important that their dosage is instead gradually tapered off. Examples of opioid analgesics include:

  • Codeine
  • Fentanyl
  • Hydrocodone
  • Hydromorphone
  • Morphine
  • Methadone
  • Oxycodone
  • Meperidine

Non-opioid Analgesics
Non-opioid analgesics are generally used to treat mild to moderate pain. Unlike opioid analgesics, they are not addictive and their pain-relieving effects do not dwindle with repeated use.
Paracetamol is classed as a mild analgesic. It is typically recommended as the first line of treatment for pain, as it is safe for most people to take and side-effects are rare. It is commonly used to treat mild to moderate pain, such as headaches, toothache, strains and sprainsParacetamol is also an effective means of reducing fevers caused by viral infections, such as colds and fluParacetamol usually starts to work within an hour, with the effects lasting on average for several hours. Do not exceed the recommended dose if it isn’t relieving your symptoms. Paracetamols mechanism of action is still not fully understood. It is thought to work by blocking specific enzymes found in the central nervous system, which in turn, dampen the sensations of painParacetamol is produced by multiple manufacturers in a wide variety of forms, including:
Unlike other pain-relief medication, paracetamol is considered safe to take during pregnancy and breastfeeding. If you are not sure whether paracetamol is safe for you, check with your doctor or pharmacist first – especially if:
  • You suffer from any form of liver or kidney problem.
  • You have issues with alcohol, such as long-term misuse.
  • You are classed as very underweight.
  • You have had an allergic reaction to paracetamol in the past.
  • You are taking other medications, which could potentially interact with paracetamol
Side-effects associated with paracetamol are quite rare but can include:
  • An allergic reaction, which can lead to rashes or swellings.
  • Low blood pressure, flushing and a fast heart rate. This side-effect usually only happens when paracetamol is administered intravenously in a hospital.
  • Liver and kidney damage.
  • Blood disorders, such as Thrombocytopenia and Leukopenia.
It is always advised to speak to your doctor or pharmacist should you develop any troublesome side-effects as a result of taking paracetamol.

Nonsteroidal anti-inflammatory drugs (NSAIDs)
These medicines can be obtained over-the-counter or as a prescription medicine, depending on the strength and dosage. NSAIDs are one of the most common pain-relieving medicines in the world. Low NSAID doses are effective for treating minor ailments, such as muscle aches, headaches, fever, minor strains and other daily discomforts. Higher doses of NSAIDs will help to relieve more moderate pain, such as joint inflammation. NSAIDs work on the chemical level by blocking the effects of certain enzymes, specifically the Cox-1 & Cox-2 enzymes. These enzymes play an important role in the production of prostaglandins, which are chemicals like hormones. When the body is injured, the damaged tissue releases prostaglandins, which amplify the pain signals from the nerves, as well as causing the damaged tissue to swell. By blocking the enzymes that produce prostaglandins, NSAIDs will effectively reduce the swelling and decrease the sensations of pain.
Ibuprofen– is manufactured by many different companies and is available in a variety of forms, including; tabletsgels, sprays and liquids. In some products, Ibuprofen is combined with other active ingredients, such as a decongestant, and sold as a cold & flu remedy. Examples of pain relief treatments containing ibuprofen include:
  • Ibuprofen (generic) – this is available as tablets, caplets, gel, and liquids.
  • Nurofen – probably the most recognised brand of Ibuprofen in The UK. Nurofen is available in a plethora of formulations including; tablets, liquid tablets, caplets, meltlets, liquids, patches, gels and sachets.
  • Cuprofen – available in tablets and gels
  • Ibuleve – available in gels, sprays, and patches
  • Brufen retard (prescription only strength)
Aspirin – belongs to the group of NSAIDs known as Salicylates. It is available in many forms and has a number of other uses besides pain relief. It can also be used to help reduce the risk of heart attacks and strokes.
Some types of Aspirin can be bought over-the-counter, while others are only available on prescription. Aspirin that can be bought over-the-counter include:
  • Aspirin (generic) – available in tablets and soluble tablets.
  • Anadin – available in tablet form
  • Dispirin – available as a soluble tablet and as a fast-tab (melts on the tongue).
Diclofenac – is used to treat mild to moderate pain, including the signs and symptoms of osteoarthritis and rheumatoid arthritis. Diclofenac can be bought as a topical gel (Voltarol), over- the-counter, or as an oral tablet with a valid prescription.
Naproxen – is usually used to treat pain and inflammation caused by conditions like; arthritis, tendinitis, bursitis, ankylosing spondylitis, gout and period painNaproxen is available in immediate, slow, or extended-release formulas. For chronic pain conditions, such as arthritis, the slow or extended release would be the preferred choice, as this form will not work fast enough to treat acute pain. Examples of Naproxen based products include; Naprosyn Tablets (prescription-only-medicine), Vimovo modified-release tablets and Feminax Ultra (over-the-counter pharmacy medicine).
Other examples of NSAIDs include:
  • Celecoxib
  • Mefenamic Acid
  • Etoricoxib
  • Indomethacin
NSAIDs can be taken by most people, however, there are some who will need to be careful about taking them. It is recommended to ask your pharmacist or doctor for advice if:
  • You are either pregnant, breastfeeding, or trying to conceive.
  • You are over 65 years of age.
  • You suffer from asthma.
  • You have suffered an allergic reaction to NSAIDs in the past.
  • You have suffered from a stomach ulcer.
  • You have problems with your heart, kidneys, liver, blood pressure, circulation, or bowels.
  • You are currently taking medicines that could potentially interact with NSAIDs.
  • You are looking to treat a child under the age of 16 years.
Under these circumstances, NSAIDs may not always need to be avoided. However, they should only be used on the advice of a healthcare professional. If deemed inappropriate, your doctor or pharmacist may recommend an alternative method of pain relief, such as paracetamol.
Like all medicines, NSAIDs carry a risk of side-effects. These will tend to be more common if you are taking higher doses for long periods of time, or if you are elderly or in poor physical health. The strengths and formulations of over-the-counter NSAIDs are generally better tolerated than the stronger prescription-only medicines. The most common side-effects associated with NSAIDs include:
  • Indigestion
  • Stomach aches
  • Diarrhoea
  • Stomach ulcers
  • Headaches
  • Drowsiness
  • Dizziness
  • Allergic reaction
Anticonvulsants used to treat chronic pain
Anticonvulsants are a group of medicines used to treat seizure disorders, but can, in some cases, be used for pain-relief. This is because anticonvulsants will also act as an adjuvant analgesic, which means it can inhibit certain types of nerve transmissions. This action will lead to a reduction of neuropathic pain sensations, such as those caused by diabetic neuropathy or trigeminal neuralgia. Examples of anticonvulsants commonly used as pain relief include:
  • Gabapentin (Neurontin)
  • Pregabalin (Lyrica)
  • Carbamazepine (Tegretol)
  • Lamotrigine (Lamictal)
  • Phenytoin Valproate
Anticonvulsants are only available with a valid prescription.
Antidepressants for chronic pain
Antidepressants can also act as an adjuvant analgesics. Although they aren’t specifically formulated as a pain relief medication, they have proven effective at treating certain types of chronic pain. Antidepressants are believed to control chronic pain in two ways. Firstly, they alter the manner in which pain is perceived from the spinal cord to the brain. Secondly, they help to reduce anxiety, which will help to improve and regulate sleep. Antidepressants can be prescribed for pain relief, either in conjunction with other analgesics or on their own. Adjuvant analgesics, like antidepressants, tend to be less effective in treating musculoskeletal pain, such as joint or back pain. However, they have proven effective at treating neuropathic pain and chronic headaches, such as tension headaches or migraines. Examples of antidepressants commonly used as pain relief:
  • Amitriptyline
  • Citalopram
  • Fluoxetine
  • Paroxetine
  • Venlafaxine
  • Nortriptyline
  • Fluvoxamine
  • Duloxetine
Antidepressants are only available with a valid prescription.
Nerve Blocks
Nerve blocks are typically used to help treat neuropathic pain. There are groups of nerves, called a plexus or ganglion, which can often cause pain to specific regions of the body. These nerves can be blocked by injecting medicine directly into the affected area, numbing the nerves and blocking the pain signals sent to the central nervous system. Nerve blocks can be used for various purposes, including:
  • Therapeutic nerve blocks – containing a local anaesthetic. These nerve blocks are typically used to relieve acute pain.
  • Diagnostic nerve blocks – these nerve blocks are designed to identify the sources of pain.
  • Prognostic nerve blocks – are used to predict the effectiveness of given treatments. This type of nerve block is aimed at determining whether more permanent forms of treatment (such as surgery) would be more effective.
  • Pre-emptive nerve blocks – this form of nerve block is designed to prevent subsequent pain, following a procedure that can cause problems.
  • Sympathetic nerve block – this type of nerve block is performed to determine whether the sympathetic nerve chain has become damaged. This chain of nerves extends the full length of the spine and is responsible for controlling some of the bodys involuntary functions, such as blood vessel dilation.
  • Stellate ganglion block – This is a form of sympathetic nerve block that assesses whether there is any damage to the nerve chain that supplies the head, neck, chest and arms, and whether this nerve damage is the source of the of the pain in those areas.
  • Facet joint block – this is also referred to as a zygapophysial joint block. The facet joints are found on the back of the spine, at the points where the vertebrae overlap. These joints are responsible for guiding and restricting spinal movements. The facet joint nerve block will help determine whether one of these joints is the source of pain.

Transcutaneous Electrical Nerve Stimulation

Transcutaneous electrical nerve stimulation (TENS) is a method of relieving pain by using mild electrical currents. A TENS machine is usually a compact, battery-operated device, which has leads connected to adhesive electrodes. These electrodes are attached directly to the skin. The machine, when switched on, will deliver mild electrical impulses through these electrodes to the affected area(s) of the body. These electrical signals are designed to reduce the pain signals being sent to the spinal cord and brain, which should dull the pain sensations, as well as relaxing the surrounding muscles. TENS stimulation can also stimulate the production of endorphins, which act as the bodys natural painkillers. TENS machines are a popular method of pain relief that can be used on a wide variety of conditions, including:

  • Back pain
  • Neck pain
  • Knee Pain
  • Sports injuries
  • Period pain
  • Arthritis

It is worth noting that TENS does not cure pain. Using a TENS machine will only provide short-term relief whilst the device is being used. Also, TENS isn’t suitable for everyone. It is important not to use a TENS machine without first seeking medical advice if:

  • Your body contains a metal or an electrical implanted device, such as a pacemaker.
  • You’re pregnant, or could be pregnant.
  • You are epileptic.
  • You suffer from heart problems.

It is commonly accepted that more research is needed to ascertain whether TENS is a reliable method for providing pain-relief. If you are considering TENS treatment, it is recommended you speak to your doctor or pharmacist first.

For some people, complementary and alternative medicines may also prove helpful for neuropathic pain relief. These treatments can include acupuncture and herbal remedies. Most alternative medicine is available without a prescription, however, it is always advised to consult your doctor before starting any new treatments for neuropathic pain.

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