What is hyperalgesia?
Hyperalgesia is an enhanced pain response. It can result from either injury to part of the body or from use of opioid painkillers.
When a person becomes more sensitive to pain as a result of taking opioid medication, it’s called opioid-induced hyperalgesia (OIH). Due to the increase in opioid usage, OIH is becoming more of a concern.
Something that typically wouldn’t cause pain will often feel painful to someone with hyperalgesia. Things that are generally painful will feel significantly more so for someone with the condition.
There are two types of hyperalgesia — primary and secondary. Primary hyperalgesia occurs at and around the site of the injury. Secondary hyperalgesia occurs when the pain feels as if it’s spreading to a non-injured site of the body.
Symptoms of OIH
The key symptom of hyperalgesia is feeling increased sensitivity to pain without additional injury or worsening of another condition.
OIH has three main symptoms:
- an increase in the intensity of the pain that you feel over time
- spread of the pain to another location other than the initial site
- an increase in the pain that you feel to external stimuli
The symptoms of OIH typically develop despite an increase in the dosage or amount of opioid taken.
It’s important to note that OIH is different from opioid tolerance. Tolerance is when a drug works less effectively over time. In people who have developed an opioid tolerance, increasing the dose of the opioid decreases pain.
Increasing the dosage of an opioid for someone with OIH will often make the pain worse.
Causes and risk factors
Nociceptors are a type of receptor on your nerves that respond to pain signals. Hyperalgesia occurs when these receptors become more sensitive.
Your body releases many compounds when part of your tissue is damaged. Some of these compounds can enhance the responsiveness of the nociceptors. This leads to the development of hyperalgesia.
Some people experience hyperalgesia following a surgical procedure. This is due to trauma to the tissue or nerves present at the surgical site. People with fibromyalgia can also experience hyperalgesia. People with shingles can develop hyperalgesia as well.
OIH can develop in people taking opioids long term for conditions such as chronic pain. It can also occur in those who are taking a short course of opioids following a surgery or procedure. Pain present in the postoperative period can promote the use of more opioid painkilling medication.
The actual incidence of OIH is unknown. Studies on the topic are limited.
How is it diagnosed?
There isn’t a set standard for diagnosing hyperalgesia. Your doctor may review your medical history as well as your medication. They must also rule out the following before giving a hyperalgesia diagnosis:
- progression of the disease for which you are being treated
- clinical worsening of the pain that is unrelated to opioid use (when OIH is suspected)
If you’re experiencing increased pain along with an increase in opioid use, your doctor will typically suspect OIH.
Treatment of hyperalgesia can be challenging, but several options are available:
Coming off of opioids completely
If you’re diagnosed with OIH, your doctor will prescribe doses of opioid that become gradually lower over time. This process can be long. Often, the pain can temporarily feel worse because your body is experiencing withdrawal from the opioid. There are additional symptoms of opioid withdrawal, but your doctor will help you through the process.
Rotating to a different class of opioids
In this option, your doctor will prescribe a different opioid in a smaller dosage. Research shows that switching to methadone (Dolophine) or buprenorphine can be particularly effective for people with OIH. However, in some cases it’s still possible to have hyperalgesia while taking methadone.
Giving an NMDA antagonist
NMDA receptor antagonists help to block the overly sensitized pain receptors in people with hyperalgesia. Ketamine has been shown to have some effectiveness in managing hyperalgesia.
Hyperalgesia is a condition in which you experience an enhanced sensitivity to pain. This is caused by specific nerve receptors in your body becoming more sensitive. Hyperalgesia can develop due to tissue or nerve injury as part of a surgery or procedure. It can also occur in people who are taking opioids.
There is no standard way to diagnose the condition. However, your doctor will rule out the progression of any preexisting condition before diagnosing hyperalgesia. Your doctor will evaluate your medical history as well as any medications before deciding on how to treat your hyperalgesia.