What are the types of allodynia?
Did you know that a terrible heartbreak can cause immense pain like having a heart attack and the same hormones that are responsible for heart failure can put someone in a life-threatening condition? This shows that pain can exist in many forms even if it seems invisible to our naked eyes and unable to see the physical damage. No matter what kind of pain is felt by one, he or she will certainly try to find the cause and relief. At this point, finding a doctor will be the best bet.
The International Association for the Study of Pain (IASP) has defined pain as an unpleasant sensory and emotional experience associated with, or resembling that associated with, actual or potential tissue damage. The definition can be quite mouthful and complicated but it helps people to understand that pain sensation does not have to be from a tissue damage such as wound or bleeding. Most certainly when a person has an actual tissue damage such as from accidentally cutting themselves with a knife, the person will feel pain. However, how can you explain a person with diabetes having pain and numbness in the leg with no sign of tissue damage? This is where the definition of pain plays a big role in helping healthcare provide the best support and treatment.
Back to the person with diabetes just now, what kind of pain just happened? This is what we call allodynia. Allodynia is a phenomenon of pain due to a stimulus that is usually not causing pain. For example, when we use cotton like a Q-tip and run through the skin, we certainly can feel the cotton but the feeling does not evoke any pain. This can be a total opposite to someone with allodynia as they will feel some degree of pain upon contact with the same cotton. The exact mechanism for allodynia remains unclear. Although, there is evidence suggesting allodynia occurs due to the sensory neuronal fibres or superficial sensory components (part of the nerve responsible to detect stimuli such as soft touch) stimulates the pain pathway, potentially due to a long-term error in potentiation. There is also evidence stating different mental states may affect this condition. In short, allodynia ultimately is caused by error in the nerve communication network.
Allodynia is a neuropathic pain since it involves the nerve. Neuropathic pain accounts for nearly 20% of the general population with almost 50% of them experiencing allodynia. Most common diseases associated with allodynia are fibromyalgia, trigeminal neuralgia, migraine and diabetes. There are three types of allodynia:
1- Dynamic or mechanical involves object movement on the skin
2- Thermal which involves temperature changes
3- Tactile or static involves gentle touch or pressure
Since allodynia is a symptom and not a diagnosis/disease, physicians may immediately suspect a person having this symptom based on asking few questions relating to the pain characteristics and possible other medical conditions. Physician will then proceed to do a simple nerve examination before deciding if there is a need for further blood tests. Imaging is rarely done unless there is suspicion of other serious disease. Although allodynia is associated with different underlying diseases, the principal treatment remains the same.
Treatments aim to relieve pain and prevent it from becoming long term. You may be surprised to know that some anticonvulsants and antidepressants are prescribed as oral medications. Topical medication containing lidocaine, menthol or capsaicin can help manage the pain. Psychological aids such as counselling, mindfulness training and cognitive behavioural therapy (CBT) may be advised to patients to help them cope with pain. When conservative treatment fails, patients may be offered for nerve block injection or surgical procedure to place the spinal cord/peripheral nerve stimulators device.
