What Is Allodynia? Symptoms, Causes, and Links to Migraine

Introduction

Allodynia is when you feel pain from something that normally is not painful. For example, a touch or temperature change causes you pain even though these are usually non-painful stimuli. Allodynia is a symptom and not a specific illness or condition, but can co-occur with other medical disorders. It is often overlooked in patients who suffer from neurological conditions such as migraines.

What Is Allodynia?

While multiple conditions can lead to allodynia, the precise mechanism is still not fully understood. It is thought to involve increased excitability in sensory nerve cells, potentially altering how mechanical stimuli are processed. These changes may cause low-threshold mechanoreceptors to activate pain-signaling (nociceptive) pathways in the spinal cord, influencing the transmission of sensory signals to the brain.

Allodynia Symptoms in Daily Life

• People with allodynia may say their head hurts when touching the pillow when lying down. They may describe pain when brushing their hair or if someone touches their wrist.
• Those living with allodynia can have difficulties with daily routines, and there can be potential misunderstandings about the condition from peers or healthcare providers.

What Are the Main Types of Allodynia?

There are different types of allodynia based on what causes pain.

• Tactile Allodynia

Pain from a light touch or pressure. For instance, your scalp hurts when brushing your hair or touching your scalp. In general, skin that is sensitive or hurts to touch is an example of tactile allodynia.

• Thermal Allodynia

This is pain from mild temperature changes, which is typically not painful

• Mechanical/Dynamic Allodynia

Pain from movement across the skin (e.g., wearing clothing)

These sensations may be associated with other medical conditions, such as migraine or neuropathic pain disorders.

Common Causes, Triggers, and Associated Conditions

Some of the causes of allodynia are as follows:

• Migraine

Allodynia is more common in people with chronic/ high-frequency migraine than in those with episodic migraine. This happens because the nerves become hypersensitive to stimuli during a migraine attack.

• Fibromyalgia

Tactile allodynia is seen in patients with fibromyalgia because they have neurochemical imbalances that lead to increased sensitivity to stimuli.

• Postherpetic Neuralgia (Shingles Complication)

Mechanical allodynia can occur in patients with postherpetic neuralgia. Shingles is caused by the herpes zoster virus, and patients may also have irritable nociceptors, leading to allodynia.

• Peripheral Neuropathy or CRPS

Allodynia can be present in patients with complex regional pain syndrome. This occurs because of central sensitization syndrome.

• Trigeminal Neuralgia

Patients with trigeminal neuralgia also experience allodynia due to sensitization.

• Diabetes

Diabetics can experience allodynia. Studies suggest that loss of the proteins SIRT1 and BDNF is linked to allodynia in diabetes.

• Medications

There are some medications that cause allodynia. For instance, a few patients taking GLP-1 receptor agonists such as semaglutide developed allodynia. This medication is used to treat obese or diabetic patients. A side effect of semaglutide is that it changes sensations in the skin. Mounjaro, tirzepatide, and WEGOVY can cause allodynia, as can chemotherapy agents, antibiotics, and metformin.

• Nutritional Deficiency

Vitamin B or vitamin D deficiency may indirectly result in allodynia, since these micronutrients are important for nervous system function.

The Migraine Link

Allodynia is a common symptom among individuals with migraines, affecting an estimated 40% to 70% of those who experience the condition. A patient who suffers from allodynia during migraines is most likely to have chronic migraines that are difficult to treat.

Pressure allodynia, brush allodynia, and cutaneous allodynia are typical of many migraine sufferers . Patients with some types of allodynia also often experience an aura (visual or sensory warning signs, like flashing lights or tingling) with their migraines.

How Is Allodynia Diagnosed?

Allodynia is diagnosed using a combination of patient history and tests.

One of the ways it can be diagnosed is using the Allodynia Symptom Checklist (ASC-12). This is based on how often patients feel discomfort during certain activities, for example, combing their hair or taking a shower.

Doctors may perform blood tests, nerve conduction studies, and electromyography.

Patients are asked to describe the pain, e.g., burning, aching, stabbing on touch, to further help doctors determine potential causes. For instance, burning or shooting pain is often due to nerve issues.

What is the difference between allodynia and hyperalgesia?

Hyperalgesia and allodynia are often confused since both are symptoms related to the sensation of pain in the body; however, they are distinct conditions. Hyperalgesia refers to an exaggerated response to a normally painful stimulus, while allodynia involves experiencing pain from a stimulus that typically does not cause pain.

Treatment Strategies

Treatment of allodynia involves both symptom relief and underlying condition management:

• Medications

Antiseizure medicines and antidepressants can be helpful in managing allodynia. If you suffer from migraines, triptans may be prescribed to treat the underlying condition causing allodynia. Lidocaine and capsaicin creams can be used on the skin.

• Interventional and Supportive Therapies

Nerve block injections and botulinum toxin can help reduce pain signals. In some cases, surgery may be needed where a device is implanted for spinal cord stimulation. Physical therapy and counseling may also help patients with allodynia.

Treatment often requires a multidisciplinary, individualized approach involving combinations of medications and therapy.

When to Seek Medical Help

If you have the following red flags, you should seek treatment promptly:

• Pain starts suddenly and is severe
• Sudden weakness
• Loss of sensation or spreading numbness
• Loss of function
• Weight loss
• Fever
• Dizziness
• Night sweats
• Fast heart rate

FAQ

How long does allodynia last?

This varies depending on why you have the condition. It can persist for months or years.

Can allodynia come and go?

Yes, but this depends on what the cause of the condition is.

Is allodynia serious?

Allodynia itself isn't a disease - it's a symptom that shows your nervous system is processing pain signals abnormally. It's still worth taking seriously because it often points to an underlying condition, and if left untreated, it can worsen and affect your quality of life.

Why does my skin hurt in one spot?

Pain in one section of your skin can be due to nerve damage.

Can anxiety cause allodynia?

Yes, it can cause or worsen allodynia.

Can COVID cause allodynia?

Yes, there are instances of patients with COVID having allodynia.

Can Lupus cause allodynia?

Yes, Lupus can cause the condition.

What can be mistaken for allodynia?

Allodynia can resemble other abnormal sensory symptoms, such as hyperalgesia, hyperpathia, paresthesia, and dysesthesia. The main difference is that allodynia is pain caused by a stimulus that normally does not hurt, whereas hyperalgesia is increased pain from a normally painful stimulus. Hyperpathia causes an abnormally painful response, particularly to repeated stimulation (often accompanied by increased threshold); paresthesia means an abnormal sensation, while dysesthesia means an abnormal sensation that is unpleasant.

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