There are several nerve or “pain” pathways in the body where signals can start to miscommunicate with each other, resulting in hyperalgesia.

Some scientists think that hyperalgesia occurs when chemicals known to reduce pain are disrupted.

Others propose that hyperalgesia happens when “crossed wires” in the nervous system prevent pain signals from transmitting accurately.

Nociceptive and neuropathic pain

Nociceptive and neuropathic are two different types of pain. Nociceptive pain is acute and it usually has a specific cause, such as an injury.

Neuropathic pain results from damage to the nervous system. It can happen even when there is no injury or outside stimulus.

Hyperalgesia is considered a form of neuropathic pain.

Doctors usually divide hyperalgesia into primary and secondary categories. Both of these conditions are due to initial tissue trauma and inflammation.

Primary hyperalgesia

This type of hyperalgesia is when the increased pain occurs in the tissue where the injury took place. An example would be when a person has surgery on their elbow, and the pain starts to worsen over time instead of improving.

Secondary hyperalgesia

This type occurs when the pain seems to spread to non-injured tissue or tissues.

Other types of hyperalgesia

Another kind of hyperalgesia is opioid-induced hyperalgesia (OIH). OIH occurs when a person experiences worsening or new pain as a result of taking opioids, such as morphine, hydrocodone, or fentanyl for pain relief.

The chief symptom of hyperalgesia is an increasingly extreme reaction to painful stimuli without any new injuries or worsening of a medical condition. An example would be a surgical incision that becomes more painful over time, yet the wound is not infected, and a person has not experienced any further injury.

Hyperalgesia is different from tolerance to medications although the two processes are similar.

If a person develops a tolerance to a particular drug, it usually means that their body has become accustomed to the presence of the drug at the current dosage, and the drug is no longer working properly. When a person has developed a tolerance to a drug, increasing the dosage will usually decrease a person’s pain.

Drug tolerance is different from hyperalgesia, where increasing pain medication will not reduce the amount of pain a person feels. Sometimes, increasing the pain medication makes the person’s pain worse.

Another similar medical condition is allodynia. This condition is where a person develops a significant pain response to non-painful stimuli. Even brushing against a person’s skin can cause pain.

In hyperalgesia, a person has experienced a painful stimulus, such as cancer pain or pain following surgery, but their response to the pain is greater than the expected level of pain.

How do doctors diagnose hyperalgesia?

Hyperalgesia can present difficulties for a doctor to treat because a person may have developed OIH.

To make a diagnosis, a doctor will take a medical history and review a person’s medication.

They may also ask them questions about the nature of their pain.

Some of the signs that could indicate hyperalgesia include:

• Pain extends beyond the area where a person experienced an initial injury or previously felt pain. Examples could include headaches, neck pain, leg pain, or back pain.
• Some people describe the pain as “diffuse” or spreading. Some may report all-over body pain and aches.
• The quality or experience of the pain is different than it used to be. The pain may become sharp, aching, or stabbing where previously the person felt the pain differently.

Currently, there are no definitive diagnostic tests for hyperalgesia.