What sort of pain have I got? – Classification of Pain

What sort of pain have I got? – a classification of pain

Essential Reading by  Dr W Allister Dow

Dr W Allister Dow MB ChB FRCA FFPMRCA Surg Cdr Royal Navy Rtd Consultant in Anaesthesia and Pain Management, Royal Surrey County Hospital

Pain can be acute or chronic, as discussed in my previous article. Pain can also be nociceptive, neuropathic, mixed, phantom, inflammatory, psychogenic, spiritual, somatic, visceral, incident or breakthrough. 

Different pains are managed in different ways so it is vital for doctors to be able to recognise what type of pain a patient is suffering.

Nociceptive pain is “Pain caused by an inflammatory or non-inflammatory response to an overt or potentially tissue-damaging stimulus”. It is the pain of damage, injury and inflammation such as a bruise, fracture or burn. It is the pain that is felt when nerve endings at the site of an injury start firing and sending damage messages to the brain. It is often described by patients as incapacitating, sharp, stabbing, throbbing, aching. It generally resolves when the damage is removed and healing begins takes place. Nociceptive pain usually responds well to conventional painkillers such as paracetamol, antiinflammatories like ibuprofen and diclofenac, and to opiates like codeine, tramadol and morphine.

Neuropathic pain is “Pain initiated or caused by a primary lesion, damage or dysfunction in the peripheral or central nervous system”. It is nerve pain and is often described by patients as shooting, electric shock, burning, crawling spiders, numbing or tingling. Patients often find neuropathic pain very difficult to put into words. Because this is pain generated inside nerves, the pain felt by the patient may actually not be in the location of the disease or damage for example in sciatica. The pain comes from a nerve being compressed and damaged at the base of the spine however the pain is felt in the leg. Other examples of neuropathic pain are pain after shingles, peripheral diabetic neuropathic pain, post stroke pain, carpal tunnel syndrome, chronic post-surgical pain and complex regional pain syndrome. The difficulty with neuropathic pain is that it is much harder to treat than acute and nociceptive pain and does not usually respond well to the conventional painkillers listed above. Drugs used to target nerve pain include some antidepressant drugs like amitriptilline and duloxetine, and some antiepileptic drugs like carbemazepine, gabapentin and pregabalin.

Mixed pain. This is when a number of different pain types co-exist therefore requiring a broader management plan and combined treatment options. The commonest seen mixed pain is low back pain with leg pain. Localised low back pain comes from a bulging or ruptured disc (a nociceptive pain) combined with sciatic pain down the back of the leg to the foot which is a neuropathic pain caused by the bulging disc pressing on and irritating a nerve root. Another mixed pain can occur in cancer. A tumour can grow, infiltrate, damage and inflame and pressurise local tissue causing nociceptive pain. The tumour can also infiltrate and damage nerves causing co-existing neuropathic pain which can sometimes be distant from where the tumour is growing.

Inflammatory pain. This is pain coming from the site of inflammation. Acute signs of inflammation are pain, swelling, stiffness, redness, heat and loss of function. Inflammation is an immune response in the body designed to eliminate the cause of the injury, clear out dead or damaged cells and tissue and to initiate tissue repair and healing. When inflammation occurs inflammatory chemicals are released which stimulate pain nerves to fire causing a nociceptive pain. It is best treated with anti-inflammatory medication like ibuprofen, diclofenac or naproxen in the form of tablets, creams, gels or suppositories.

Phantom pain is the pain felt in part of the body which has been traumatically lost or surgically amputated, or pain from a part of the body from which the brain no longer receives signals. It is a type of neuropathic pain.

Psychogenic pain is also called somatoform pain. It is pain that is caused, increased or prolongued by emotional, mental, behavioural or psychiatric factors. These patients often feel stigmatised and can feel that people do not believe that they are in pain. They can sometimes be misdiagnosed as suffering hysteria, anxiety disorder, neuroticism, depression or hypochondriasis. These patients are often best managed under a pain clinic multi-disciplinary team with doctors, nurses, physios and psychologists involved in their care and treatment. Fibromyalgia may be a somatoform pain disorder but it is still not well understood.

Spiritual pain is a form of psychogenic pain and is commonly seen following bereavement. It is also sometimes seen as part of an ‘empty-nest syndrome’ in which children have grown up and left home and mothers develop a psychological pain like a bereavement, through lack of purpose and direction in life.

Breakthrough pain. This is seen in patients who live with a level of chronic pain but suffer intermittent short lived, acute increases in their background pain level on top of their normal pain. It is often unpredictable and is not alleviated by the patient’s normal pain management . It is common in patients with cancer pain and treatment can entail using short acting strong opiate preparations like fentanyl in the form of liquids, oral melts, sprays or lollypops.

Incident pain is pain that arises as a result of activity such as stretching a wound or movement in an arthritic joint. It is nociceptive and predictable.

Somatic and visceral pain. Somatic pain is pain coming up to the brain through nerves from pain receptors (nociceptors) in the skin and deep tissues. These nerves called A-delta nerves carry pain messages at a speed of 50-100 metres per second! These nociceptors respond to sensations related to temperature, vibration and pressure/stretch/swelling. Somatic pain is of course a nociceptive pain. Visceral pain is also nociceptive pain but is coming from the internal organs through slower pain nerves called C-fibres. These carry pain signals at 2-3 metres per second Visceral pain feels different to somatic pain and is often described as deep, squeezing, pressure, aching. It is harder to locate and pinpoint and can be a more generalised pain. It is caused by compression, squeezing, stretching or damage within an organ. Visceral pain can radiate and be felt in other areas of the body for example gall stone or biliary pain can be felt in the right shoulder whereas cardiac pain from angina or heart attack can be felt in the left arm. 

If you have acute or chronic pain, try and work out with the help of your doctor where the pain is coming from and what sort of pain it is. This will help to guide the best treatments for your pain. If your pain is continuing despite treatments offered by your GP then please ask for a referral to your local Pain Clinic.
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