If the neck has been injured or has an overall pain condition, the legs and the arms may exhibit disturbances in sensory reactions even though these areas are not symptomatic. Local hyperalgesia is described as an abnormally high pain response to a stimulus which would be normally painful, and this may be because the local nerve structures in the neck have become oversensitive to incoming feelings. The more widespread reactions are more likely to result from the central nervous system processing differently to normal. The more widespread upsets in sensory systems may help divide whiplash from less serious neck pains.
Whiplash patients have generally higher levels of disability and pain and show more widespread pain on clinical examination. Patients with nerve root problems in the neck and those with whiplash associated disorder (WAD) both share features of sensory abnormality which may indicate that the underlying changes in the processing of pain are similar in both conditions. Another piece of evidence which may back up the role of central systems in these presentations is the occurrence of allodynia. Allodynia is the presence of pain in response to a normally non-painful stimulus such as touching, brushing or wearing clothes.
The abnormalities in sensory mechanisms which have been found in chronic whiplash patients have been shown to be present just after the time of injury. All whiplash sufferers, irrespective of their severity, develop some hyperalgesia to local mechanical stimuli but in milder injuries and good recovery this settles over two or three months. Those with higher pain and chronic symptoms have persistent hyperalgesia symptoms which may not change from the early period. It is known that musculoskeletal pain patients can have their pain thresholds altered by the presence of anxiety or other psychological distress.
It is clear that psychological distress is a feature of patients with whiplash syndrome, with more highly distressed patients having higher levels of pain and disability. However it does not appear that the increased pain sensitivity is caused by psychological distress but that the pain and the distress may be consequences of the heightened sensitivity in the central nervous system. Apart from these findings, investigations have also shown that patients can have an exaggerated pain reaction to cold and changes in the way the blood vessels constrict.
If a peripheral nerve is injured in the body then patients can develop the pain of cold overreaction and as this occurs in whiplash this may imply that some nerve injury is involved in both cases. A lesion of one of the cervical nerve roots can also cause the cold overreaction response and this again could link it to the same symptom presentation in whiplash. An overreaction to cold, cervical burning pain and sudden electric shock are all neuropathic pains, pains caused by abnormal responses in the nervous system, and have been identified in groups of patients with acute whiplash syndrome.
Many of the sensory findings in the neck may not easily translate into ways of managing whiplash by physiotherapy. However, if there is only local hyperalgesia in response to mechanical inputs and no other sensory abnormalities, then the local neck structures may be oversensitive due to the injury to the neck tissues. This kind of local abnormality has been shown to react favourably to physiotherapy or other manual therapies. Exercise may also reduce this type of increased nerve reactions and also improves the ways the muscles coordinate, improving the management of neck pain.
It takes much more careful judgment and planning to treat a patient who has the added symptoms of neuropathic pain, the allodynia, the widespread sensitivity and the cold overreaction. Stirring up the pain and other symptoms in treatment will only reinforce the abnormal neural processing and worsen the pain. Manipulative and manual techniques need to be much more gently applied and there is some evidence that physiotherapy can be useful in the overall management of whiplash disorder.
This approach works less well however if patients exhibit the cold overreaction symptoms. Those patients with neuropathic symptoms show significantly higher reports of disability and pain and a physiotherapy treatment approach is not clear, with only thirty percent of patients exhibiting pain improvement from medication.