Hyperalgesia is when you have extreme sensitivity to pain. If you have this condition, your body overreacts to painful stimuli, making you feel increased pain. You can develop hyperalgesia if you use opioid drugs or injure a body part.
Hyperalgesia vs. Allodynia
Hyperalgesia is different from allodynia.
Allodynia is when things that don’t usually cause pain suddenly seem to be painful. When you have allodynia, you feel pain even if an object brushes against you. If you have migraines, you may be familiar with migraine-induced allodynia, when you become sensitive to even the slightest touch.
With hyperalgesia, things that normally cause pain feel more painful than usual. For example, you are likely to feel extreme pain in a previously injured body part.
Types of Hyperalgesia
Your pain response abnormally increases if you have an injury or use opioids. They make you more sensitive to pain and increase your risk of developing hyperalgesia.
There are different kinds of hyperalgesia:
Opioid-induced hyperalgesia. This refers to the increased pain sensitivity you feel after taking opioids like heroin, morphine, or fentanyl. Opioids are generally used as painkillers. But high doses can reverse their effects and increase your pain.
Injury-induced hyperalgesia. This refers to an increased pain response caused by an injury to your tissues or nerves. You may even have it after surgery.
It can have two subtypes:
- Primary hyperalgesia, which is extreme pain around your injured body part
- Secondary hyperalgesia, which is when the pain seems to spread from the injured part to other parts of your body
Causes of Hyperalgesia
Hyperalgesia happens when your body’s pain receptors or nociceptors become damaged or sensitive. When you have an injury, your body releases pain signals. These signals stimulate your nociceptors and increase your pain response. This can cause hyperalgesia.
If you take opioids or opioid painkillers, you can develop opioid-induced hyperalgesia. Although opioids are used as painkillers, higher doses can make your nociceptors more sensitive to painful stimuli. This enhances your pain response and makes you feel extreme pain.
You may also have hyperalgesia due to:
Symptoms of Hyperalgesia
The main symptom of hyperalgesia is high sensitivity to pain.
If your condition is sparked by an injury, you may experience:
- Primary hyperalgesia. Even if you have no new injury or complication, you may feel extreme pain near a previously injured site.
- Secondary hyperalgesia. Your pain may seem to spread to other body parts.
The symptoms of opioid-induced hyperalgesia depend on the dose of opioids you take.
If you have this condition, you may experience:
- Increased intensity of pain over time
- Pain extending to sites other than the injured part
- Enhanced pain response to stimuli
The symptoms of opioid-induced hyperalgesia can be confused with those of opioid tolerance.
If you have opioid tolerance, you may feel increasing pain over time. This may be because the dose you take is no longer enough to treat your pain. In such cases, the dose of the opioid must be increased to reduce your pain.
But with opioid-induced hyperalgesia, increasing the opioid dose will further increase your pain.
Diagnosis of Hyperalgesia
Hyperalgesia can be difficult to diagnose as it doesn’t have a standard detection method.
Typically, your doctor will check if you have symptoms, and look at your medical history and the medications you take. They may check for recent injuries or underlying diseases.
Your doctor will immediately suspect opioid-induced hyperalgesia if you experience extreme pain after increasing your opioid dose.
Treatment for Hyperalgesia
Hyperalgesia can be treated using the following methods:
Decreasing your opioid dose over time. If your hyperalgesia is caused by opioid use, your doctor will have you gradually decrease your opioid dose. Due to the long treatment period, you may have extreme pain and opioid withdrawal symptoms. But your doctor will help you manage your symptoms.
Switching to other opioid medicines or opioid rotation. Your doctor may prescribe smaller doses of a different opioid. Opioids like methadone, oxycodone, or tramadol are reported to be effective against opioid-induced hyperalgesia.
Using N-methyl-D-aspartate (NMDA) receptor antagonist drugs. Research has shown that NMDA receptors are responsible for increasing your sensitivity to pain. NMDA receptor antagonists are drugs that block your pain receptors, suppress your pain response, and reduce your pain. Ketamine and methadone are common NMDA receptor antagonists that are useful for treating hyperalgesia.
Complications and Other Considerations
The treatment method may vary among people based on your body's response to an individual opioid. You may have opioid medication side effects such as dizziness, drowsiness, vomiting, constipation, itchy skin, dry mouth, or respiratory depression.
When your doctor switches or reduces your opioid drugs, you may feel increased pain. You may also have withdrawal symptoms such as sweating, restlessness, anxiety, or cramps. If you still have extreme pain, talk to your doctor to lower or switch your opioid dose.