What is Allodynia & How is it Treated?|Causes, Symptoms, and Diagnosis of Allodynia

Allodynia is a rare symptom that can occur due to problems with the nerves. It is a feeling of pain from a stimulus that normally does not cause pain, such as touching the skin lightly or brushing hair.

A study done in 2014 stated that 15-50% of people with neuropathic pain experience allodynia.⁽¹⁾

Allodynia is of three types:⁽²⁾

• Thermal Allodynia: In this type of allodynia, pain occurs with a mild change of temperature on the skin. For example, falling of a few drops of cold water on the skin may bring pain.
• Dynamic or Mechanical Allodynia: There may be pain if anything is moved on the skin. For example, moving across a bedsheet on the skin may cause pain.
• Static or Tactile Allodynia: Slight pressure on the skin, such as a light tap may cause pain.

A person can have one or all types of allodynia.

Allodynia can affect any part of the body depending on the type of allodynia and its underlying cause.

Allodynia is a type of pain that cause sensitization. Its exact cause is not known, but it is believed to occur due to the following reasons:

• Sensitization can occur due to the nerves getting damaged or hypersensitive.⁽³⁾ This can cause the nerve endings to release neurotransmitters leading to nerve inflammation. This can result in allodynia or hyperalgesia.
• Allodynia can also occur if the nerve carries pain messages incorrectly due to the crossing over of the nerve fibers.⁽⁴⁾ It can lead to increased responsiveness or malfunction in nociceptors, a type of nerve ending.
• Damage to the nerve can occur due to a health condition or injury. It can also occur due to no apparent reason.

There are also a few medical conditions that may increase the risk of allodynia in a person, these include:

• Migraine: It is observed that 65% of people with migraine experience the symptoms of allodynia during the time of an attack and 20% among them may have cutaneous allodynia.⁽⁴⁾
• Postherpetic Neuralgia: It is a complication of shingles, which causes damage to the nerve fibers. A study states that most people with postherpetic neuralgia experienced symptoms of tactile allodynia.⁽⁵⁾
• Diabetic Neuropathy: Diabetes can lead to damage to the nerves and increase the risk of nerve pain. The nerve growth factor is essential for the nervous system and some experts suggested that diabetes lowers its levels. A rodent study linked lower levels of nerve growth factors with hyperalgesia or allodynia.⁽⁶⁾
• Chemotherapy: Chemotherapy can lead to nerve damage and can cause allodynia. A study done on mice indicated that chemotherapy could induce mechanical allodynia.⁽⁷⁾ Research also suggested that mechanical or thermal allodynia occurs in people experiencing chemotherapy-induced peripheral neuropathy.⁽⁸⁾

Pain from a stimulus that normally does not cause pain is the main symptom of allodynia.

Some people may find hot and cold temperatures painful, some may have pain from gentle pressure on the skin. The pain might be a response to a brushing sensation or movement along the skin or hair.

Depending on the cause of allodynia there may be other symptoms as well.

If allodynia occurs due to fibromyalgia, a person may experience:

• Anxiety
• Depression
• Trouble concentrating
• Fatigue
• Trouble sleeping

If migraine is the cause of allodynia, there may be:

• Painful headaches
• Nausea
• Changes in vision
• Increased sensitivity to light

A doctor takes the medical history of the patient, performs a physical exam, and reviews the symptoms.

The doctor enquires about the duration, intensity, time, and frequency of symptoms. He enquires if the patient has taken any medication or if there is anything that relieves pain.

In the physical examination the doctor may check by delivering light touch to the area, testing the reflexes, touching the skin with a cold device, or looking for skin changes.

Also, tests may be performed to rule out any other conditions.

Lifestyle changes do not treat allodynia but can help people with it, lead an easy life. The lifestyle changes include:

• Light exercises
• Taking a well-balanced diet
• Quitting smoking as it is observed that smokers are more at risk of experiencing chronic pain⁽⁹⁾
• Getting enough sleep
• A person can also identify triggers and try and avoid them.

Some complementary approaches such as cupping and acupuncture can be helpful in getting relief from the symptoms

Medically too allodynia has no cure but there are certain treatments that can reduce pain. These include anticonvulsants, anti-depressants, topical pain medications, and other topical treatments.

Physical therapy, counseling, nerve blocks, and nerve stimulators may also be recommended. Surgery can be an option if any specific nerve is responsible for causing allodynia.

Allodynia is not a life-threatening condition but can make life challenging. It may also lead to anxiety or other mental health condition. Its outlook depends on the severity of symptoms and the underlying condition.