Chronic pain is a complex state in which pain produces changes throughout the central nervous system (CNS).  The changes have a particular and complex effect on the emotional systems; with pain causing depression and depression causing pain.
Research is beginning to reveal how and where the brain processes pain information, and how that may be affected by specific neurological illnesses. Chronic pain may be the direct result of neurological disease, perhaps even integral to some diseases like Parkinson’s Disease (PD).
- Studies have shown that people with dementia are at risk of under treatment for pain
- There is no evidence to show that they are less likely to have pain
- Even in advanced dementia a person will still feel pain, but may not recognise it or be able to respond in a normal manner
- A person with advanced dementia may respond to pain by changes in behaviour, or mood eg, grimacing, aggression, agitation and withdrawal
- Pain may interrupt sleep patterns of people with dementia 
- Effectively managing the pain of people with dementia may reduce other symptoms. Improved pain management may also reduce the stress of persons caring for people with advanced dementia [3,4]
- It is possible that people with frontotemporal dementia (Pick's disease) may have a reduced response to analgesia because the expectation or placebo effect is disrupted. 
- Key elements of a Palliative Approach for People with Severe and End Stage Dementia (759kb pdf) is a booklet developed for health care professionals through a collaboration between Curtin University, Alzheimer's Australia and the Menzies Research Institute.
- Pain is a common symptom in PD, affecting 40-60% of people with PD
- People with PD report different types of pain, most commonly muscular skeletal pain, but they report the severest is due to changes in muscle tone and muscle spasms
- They may also experience nerve pain particularly back pain but also burning and tingling sensations
- Some people with PD experience unusual and disabling pain syndromes for which a cause is hard to identify. It is thought that this pain is due to changes in the brain due to PD.
- People with PD may also experience akathisia, an inner restlessness that produces a constant need to keep moving. 
- Lower levels of dopamine lowers the pain threshold and increase the pain sensation for people with PD:
- people with PD may experience 'ON' and 'OFF' periods as the effects of Parkinson medication wears off
- people with PD have increased pain in the 'OFF' time
- administering anti Parkinson’s medication on time and adjusting the treatment schedule to minimise 'OFF' periods may also be a pain management strategy. 
- Damage to the brain from stroke may produce central pain syndromes and central post-stroke pain
- stroke may also change the way a person responds to pain. They may have a reduced emotional response to pain. 
Pain and Multiple Sclerosis is a guide produced by the MS Society of Australia for health professionals. It reviews current knowledge on the aetiology and management of pain in people with MS.
Some key points about pain and MS described in this document are:
- people with MS experience many types of pain:
- nociceptive pain
- neuropathic pain
- episodic pain with exacerbations of MS
- chronic pain
- paroxysmal acute pain.
- pain is a common symptom in MS
- pain may have a severe impact on quality of life for people living with MS
- pain in MS is very complex and often complicated by anxiety and depression
- physical activity may produce short term increase in pain. Prescribed exercise has been shown to reduce pain overall
- the treatment of acute pain in MS is the treatment of the cause of the pain
- people with MS have reduced sensation and may have abnormal responses to stimuli (eg, use hot and cold therapies with caution)
Papers about pain and pain management often use terms that may not be commonly understood in RAC. The following definitions may be of assistance if you wish to read further on this subject:
- allodynia: pain due to a stimulus that does not usually cause pain
- central pain: pain that begins in the central nervous system or is caused by a lesion in the CNS
- neuralgia: pain along the distribution of a nerve or nerves
- neuropathic pain: pain that is due to a lesion or to dysfunction in the nervous system
- nociceptive pain: pain that is associated to harmful stimulation of peripheral nerve fibres of the skin, joints and organs. This can be associated to mechanical, chemical or thermal irritation of these fibres.