Defining painPain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage or described in terms of damage. Pain sensation is essential to the survival, wellbeing, learning and adaptation of human beings..The ability to detect harmful stimuli is a key function of the nervous system through which humans interact with the ever changing environment to anticipate, plan, react and adapt. However, pain may become pathological when it is no longer useful as an acute warning system and instead becomes chronic and debilitating.Classification of pain statesPain is the most common presenting symptom in health care. It is necessary to classify pain states to provide an understanding of pain disorders, establish standards for diagnosis and description and allow the exchange of standardised information. Although it may be classified in many ways, pain is generally classified as nociceptive, neuropathic, idiopathic, psychogenic and mixed.Common pain statesAcute PainAcute pain begins suddenly and is usually sharp in quality. It serves as a warning of a disease or a threat to the body. Acute pain may be mild and last just a moment, or it may be severe and last for weeks or months. In most cases, acute pain does not last longer than 3-6 months and it disappears when the underlying cause of the pain has been treated or has healed. Typical acute pain states include surgical pain, traumatic pain, labour pain and ischemic pain.Chronic painUnrelieved acute pain may lead to chronic pain. Chronic pain persists longer than 6 months, even though the injury has healed. Physical effects of pain include tense muscles, limited mobility, lack of energy and changes in sleep and appetite. The emotional effects include depression, anger, anxiety and fear of re-injury. These effects frequently hinder a person's ability to return to normal work or leisure activities.Typical chronic pain conditions include neuropathic pain, arthritic pain and fibromyalgia (a muscular or musculoskeletal pain with stiffness and tenderness in the body).Neuropathic painNeuropathic pain is caused by damage or disease affecting any part of the somatosensory system (a part of the sensory nervous system responsible for sensation). Peripheral neuropathic pain is caused by damage ordysfunction of peripheral nerves. Painful diabetic neuropathy, complex regional pain syndrome Type 2 (causalgia or intense and prolonged pain), postherpetic neuralgia (persistent pain that occurs long after rashes disappear in shingles) and radicular pain (pain radiating from the back and hip through the spine) are examples of this type of pain. Neuropathic pain is often described as "burning," "tingling," "electrical," "stabbing," or "pins and needles." Central pain is caused by a primary injury or dysfunction in the central nervous system and is usually associated with abnormal sensitivity to temperature and tissue-damaging stimulation. Common examples include post-stroke pain, pain related to spinal cord injury and pain due to multiple sclerosis. Phantom pain (pain felt in a part of the body that has been lost or from which the brain no longer receives signals) may also be considered in this category.Nociceptive painNociceptive pain is caused by activation of nociceptive afferent fibres and typically through thermal, mechanical or chemical stimulation. This is carried through a network of neurons spread across the body that collect pain signals or information fromdifferent body parts and send them to the spinal cord for transmission to the brain. Based on the location of the nociceptors (pain receptors) in the body parts, nociceptive pain may also be divided into visceral pain, deep somatic pain and superficial somatic pain.Idiopathic painIdiopathic pain is a pain that persists after the trauma has healed or that arises without any apparent cause. Some argue that such pain occurs in the mind of a person.Psychogenic painPsychogenic pain is pain caused, increased or prolonged by mental, emotional or behavioural factors.Mixed type of painMany types of pain can co-exist in the same individual, leading to a mixed type of pain. Examples of this type of pain include complex regional pain syndrome (CRPS) and fibromyalgia. In such circumstances, identifying the chief component of the pain may facilitate the planning of therapeutic strategies.Complex regional pain syndrome is a chronic systemic condition of severe pain, swelling and changes in the skin. It often initially affects an arm or a leg and spreads throughout the body. It is a multifactorial disorder with signs of neurogenic inflammation, nociceptive sensitization, vasomotor (changes in the diameter of blood vessels) dysfunction and maladaptive neuroplasticity (brain's ability to change and adapt as a result of an experience), generated by an abnormal response to tissue injury. There are two types of CRPS - Type 1 and Type 2.Abromyalgia is characterised by chronic widespread pain and allodynia (a heightened and painful response to pressure). Its exact cause is unknown but is believed to involve psychological, genetic, neurobiological and environmental factors that lead to an increased response of sensation to the central nervous system.Abromyalgia symptoms are not restricted to pain and include debilitating fatigue, sleep disturbance and joint stiffness.Pain assessment and treatmentTherapeutic strategies depend on proper clinical assessment and understanding of the pain condition affecting each person. Adequate and effective clinical assessment with appropriate methodology (history, physical exam, and diagnostic imaging and diagnostic procedures) holds the key to developing a clinical understanding of the pain conditions in question. Effective treatment of pain involves mechanistic therapy, evidence-based therapy, and personalized therapy.Examples of mechanistic therapy include antivirals for herpes zoster, decompression of spinal stenosis for neurogenic claudication and pain, and control of blood sugar levels in cases of diabetic neuropathy.Examples of evidence-based therapy include spinal cord stimulation for failed back surgery syndrome, radiofrequency ablation of facet joint innervation for neck and back pain and medications for neuropathic pain.Mechanistic or evidence-based therapy may not be readily available for many painful conditions and also because each person is unique in their presentation of pain and responses to pain therapy. Therefore, it is extremely important to weigh the risks and benefits of the available treatment options and tailor therapeutic strategies to fit the individual needs of each person.Dr Manas Manohar is a Pain ManagementConsultant.