What is pain?
Pain is a warning, and when you feel pain you know at once that something is wrong. The type of pain and where in your body you feel it, gives clues about what is causing the pain. Pain receptors, called nociceptors, are stimulated by triggers that indicate potential damage to the body, such as mechanical forces, chemicals, and extreme heat. Messages received by pain receptors are sent to the brain to be processed and interpreted as pain. Burns, cuts, fractures, sprains, and inflammation are examples of nociceptive pain. This type of pain is usually perceived as aching or throbbing, ranging from mild to severe.
Pain can also be acute or chronic. Acute pain, such as following an injury or surgery, usually stops as soon as the initial cause has healed. However, if the pain continues more than six months, it becomes chronic pain, which is often related to a chronic progressive condition like arthritis.
Types of pain
The inflammatory response to injury and infection is a process that involves cells of the immune system and a range of chemicals produced to protect and heal the injured or infected tissues. If the inflammation continues after the body has recovered from the injury, chronic inflammation can cause damage such as chronic degenerative joint diseases. Symptoms of inflammation include redness, swelling, and pain.
Pain due to inflammation is caused by chemicals, such as prostaglandins and leukotrienes, produced by immune cells produced during the inflammatory response. It includes.
- Soft tissue injury triggers inflammation such as sprains and strains due to trauma and sports injuries. Overuse injuries also cause inflammation of tendons (tendinitis, tennis elbow) and inflammation within joints (bursitis and frozen shoulder).
- Pain following surgery is caused by inflammation.
- Osteoarthritis often called wear and tear, is caused by the gradual destruction of the cartilage that covers and protects the ends of the bones in an articular joint. The underlying bones rub against each other, causing inflammation, pain, and stiffness, which restricts the movement of that joint.
- Rheumatoid arthritis is an autoimmune disease where the immune system attacks and destroys the synovial membrane that forms a protective lining over the joints. The synovium becomes inflamed and thickened, causing swelling and pain in the joints. Eventually, the cartilage and bone are damaged, which can cause deformities.
A migraine is a neurological disorder that causes an intense, throbbing, and painful headache, usually with other symptoms including nausea, vomiting, and extreme sensitivity to light. An aura can be the first sign of a migraine attack and includes visual disturbances like zig-zag lines and blurring.
A migraine attack is thought to be triggered by the abnormal release of chemicals in the brain that causes inflammation, pain, and extreme widening (dilation) of brain blood vessels. Activation of nearby sensory trigeminal nerves also induces pain and other symptoms of a migraine.
Genetics is known to play a role as well as specific triggers, including stress, hunger, hormonal changes, some foods like cheese or chocolate, caffein-containing drinks like coffee, and alcohol, amongst others.
Nerve pain is a different type of pain and is the result of a damaged or malfunctioning nervous system. Although an injury may be the original trigger, nerve pain continues after the wound has healed because the nervous system has become sensitised. The nerve pain generated may now be unrelated to the initial injury. Also, nerve pain sensation is different and is described as electric shocks, stabbing, and burning.
Examples of nerve pain include shingles, trigeminal neuralgia (affects the face and teeth), sciatica (compression of nerves in the spine), phantom limb pain following amputation, and diabetic neuropathy, where peripheral nerves are damaged mainly in the legs and feet.
Neurotransmitters are brain chemicals that allow nerve cells to communicate. A balance between excitatory and calming neurotransmitters is essential for the brain to function normally. An imbalance in these neurotransmitters is thought to be involved in causing nerve pain.
Gout and kidney stones
Gout is caused by excess uric acid in the blood. Uric acid crystals become deposited in the skin, known as tophi, in the kidneys, known as kidney stones, and in the joints, known as gout. Uric acid crystals cause inflammation, pain, and swelling.
Primary dysmenorrhoea is a common problem for many women, causing painful periods. At the end of the menstrual cycle, prostaglandins stimulate the uterine muscle to contract and expel the uterine lining. Prostaglandins are cellular messengers that mediate many cellular processes. Production of prostaglandins in large amounts can result in increased contractions causing muscle cramps and menstrual pain.
Muscle spasm is involuntary and excessive muscle contraction and can be very painful. This type of muscle spasm is called spasticity or muscle stiffness. Clonus is a reflex muscle spasm caused by a series of spontaneous involuntary muscle contractions and relaxations. Muscle spasm can be due to nervous system disorders like multiple sclerosis, motor neuron disease, and cerebral palsy. Other causes include meningitis, a tumour, following a stroke, or injury to the brain and spinal cord.
Medications for pain
Nonsteroidal anti-inflammatory drugs (NSAID)
Nonsteroidal anti-inflammatory drugs (NSAID) are used to relieve the pain of inflammation. These include diclofenac, indomethacin, meloxicam, and celecoxib. All NSAIDs work by inhibiting the action of the enzyme cyclooxygenase (COX). This enzyme is critical for the synthesis of chemicals called prostaglandins (PG). Prostaglandins are cellular messengers that mediate many processes. Some prostaglandins like PGE2 are produced at sites of injury or inflammation and cause pain, swelling, and other symptoms of inflammation.
There are two forms of COX enzyme. COX-1 is produced by most cells, including the stomach, and resulting prostaglandins protect the stomach lining. COX-2 is only induced during the inflammation process and results in the synthesis of inflammatory prostaglandins, particularly PGE2. Diclofenac and indomethacin are both non-specific COX inhibitors and block the production of both COX-1 and COX-2. This can cause gastrointestinal side effects due to the inhibition of protective prostaglandins and the disruption of acid regulation. Celecoxib and meloxicam are specific COX 2 inhibitors and only block prostaglandins that are induced during an inflammatory response. Diclofenac and indomethacin are used to treat acute and chronic musculoskeletal inflammatory pain, post-operative pain, arthritis (rheumatoid arthritis and osteoarthritis), and dysmenorrhea. Celecoxib and meloxicam are used primarily to treat rheumatoid arthritis and osteoarthritis. However, celecoxib is also used to treat dysmenorrhea.
Sumatriptan and rizatriptan drugs called triptans that are used to treat migraine attack to relieve headache and other symptoms. They work by mimicking the actions of the brain chemical serotonin, a neurotransmitter that causes blood vessels to constrict and narrow. These drugs also block the transmission of pain signals.
Nerve pain drugs
Gabapentin is an anticonvulsant that is used to treat epilepsy. It also works by the same mechanism to relieve nerve pain. Gabapentin acts directly on nerve cells in the brain to prevent abnormal electrical activity and repetitive transmission of nerve impulses. Gabapentin blocks the transmission of excitatory nerve signals, which reduces the amount of nerve excitation that causes epileptic seizures and nerve pain.
Allopurinol is used to treat conditions caused by uric acid crystals, such as gout, kidney stones, and skin tophi. Allopurinol works by inhibiting the enzyme xanthine oxidase, which plays an important role in the production of uric acid. This prevents the build-up of uric acid in the blood and helps relieve the pain caused by deposits of uric acid crystal.
Baclofen is a muscle relaxant that is used to help relieve painful muscle spasm caused by a variety of injuries and conditions. Baclofen works by acting directly on nerve cells in the brain to control nerve signals sent to muscle cells that cause them to contract. This prevents excessive and involuntary muscle contraction causing muscle spasm.