Mildly painful stimuli perceived as severe pain.
Hyperalgesia is the abnormally increased sensitivity to pain, which may be caused by damage to nociceptors or peripheral nerves and can cause hypersensitivity to stimulus.
Prostaglandins E and F are largely responsible for sensitizing the nociceptors.
Temporary increased sensitivity to pain occurs as part of sickness, a response to infection.
Hyperalgesia can be experienced in focal, discrete areas, or as a more diffuse, body-wide form.
It is possible to experience a learned hyperalgesia of a diffuse body-wide form.
The focal form is typically associated with injury, and is divided into two subtypes:
Primary hyperalgesia describes pain sensitivity that occurs directly in the damaged tissues.
Secondary hyperalgesia describes pain sensitivity that occurs in surrounding undamaged tissues.
Opioid-induced hyperalgesia may develop as a result of long-term opioid use in the treatment of chronic pain.
Primary or secondary hyperalgesia can develop in response to both chronic and acute exposure to opioids.
Hyperalgesia is induced by platelet-activating factor (PAF) from an inflammatory or an allergic response, with immune cells interacting with the peripheral nervous system and releasing pain-producing chemicals of cytokines and chemokines.
Chronic hyperstimulation of opioid receptors results in altered homeostasis of pain signalling pathways in the body with several mechanisms of action involved.
Blocking the nociceptor receptor, may be a means of preventing the development of hyperalgesia.
Amplification in the spinal cord may be another way of producing hyperalgesia.
The release of proinflammatory cytokines such as interleukin-1 by activated leukocytes triggered by lipopolysaccharides, endotoxins and other signals of infection also increases pain sensitivity as part of the response to illness.
Diagnosis:
Quantitative sensory testing can be used to determine pain thresholds and stimulus/response functions to indicate hyperalgesia.
Mechanical allodynia can be assessed using a cotton swab or a brush.
A pressure meter and monofilaments or weighted pinprick stimuli are used for assessing pressure and punctate allodynia.
A thermal tester is used for thermal testing.
Treatment:
Hyperalgesia is similar to other sorts of pain and may respond to standard treatment for these conditions, using various drugs such as SSRI or tricyclic antidepressants: Nonsteroidal anti-inflammatory drugs (NSAIDs), glucocorticoids, gabapentin or pregabalin, NMDA or atypical opioids such as tramadol.
The use of a transcutaneous electrical nerve stimulation device has been shown to alleviate hyperalgesia.