Hey guys! I truly believe that having an understanding of how pain works within the body can help people overcome pain. This blog post is meant to summarize a peer-reviewed article in a medical journal known as the “Journal of Neural Transmission”. This specific article focused on neuropathic pain from a purely biological perspective. Keep in mind that this article does not apply to all types of chronic pain, but more specifically to conditions where specific nerves have been damaged. I’d also like readers to remember that there are also psychosocial perspectives on understanding neuropathic pain that have not been mentioned in this article. This article is meant for purely educational purposes and is not meant to imply whether a condition is treatable or untreatable. Here at Chronic Pain Hope, we believe that all types of pain can be significantly reduced, regardless of the type or cause. Hang onto hope and keep learning about pain.

What is neuropathic pain?

• A chronic condition caused by a lesion or disease of the central or peripheral nervous somatosensory nervous system (Rosenberger et al., 2020). Not all patients who have lesions or neural disorders develop neuropathic pain. Whether or not they develop neuropathic pain is influenced by psychosocial, genetic, biological, and clinical risk factors (Rosenberger et al., 2020)

• Examples of neuropathic pain include carpal tunnel syndrome, post-surgical pain, painful radiculopathy, cancer pain, phantom limb pain, post-herpetic neuralgia, HIV neuropathy, Guillain-Barre syndrome, chemotherapy induced peripheral neuropathy, etc. (Rosenberger et al., 2020)

• It is estimated that 6.9-10% of general population has neuropathic pain.

Types of Neuropathic Pain

• There are two major types of neuropathic pain: central and peripheral

• Central neuropathic pain impacts the brain and spinal cord leading to amplified processing of pain.

• Peripheral impacts the nerves throughout the rest of the body which reduce signal transmissions to the spinal cord and leads to alterations in gene expression patterns.

• When a peripheral nerve injury occurs the connection between periphery and central nervous system breaks down resulting in sensory loss. Neuroimaging studies suggest that people also experience neurodegeneration in the brain.

Sensitization in the Peripheral Nerves

• Sensitization can be defined as an increase in the magnitude of the response to noxious stimuli. This means something that had once caused very little pain now causes more severe pain.

• This sensitization usually develops as a consequence of tissue injury and/or inflammation.

• Researchers have discovered a family of receptors known as TRP channels. These channels can be activated by various stimuli, including physical and chemical signals. When they become sensitized, they are more responsive and lead to an increase in pain sensitivity. They generate electrical signals that increase pain. They can fire signals when there is no obvious reason for pain.

• Inflammation makes these TRP channels more sensitive.

• When nerves are damaged, the immune cells gather at the damaged site and release substances that make the nerves more sensitive to pain.

• Ultimately whenever there is nerve damage, a chain reaction that involves both the nervous and immune systems is activated. This chain reaction causes an increased sensitivity to pain.

Central sensitization

• Defined as “an increased responsiveness of nociceptive neurons in the CNS to their normal or subthreshold afferent input”

• This means there is heightened sensitivity in the brain and spinal cord to stimuli. Much like peripheral sensitization, stimuli that had once caused very little pain now causes more severe pain.

• This sensitivity is caused by persistent input from damaged nerves. Blocking the signals from damaged nerves can stop the pain.

• The nerves and the central nervous system start to change in response to pain. These changes include changes in calcium levels, gene changes, and the activity of certain proteins.

• There are medications that can help calm down the hyperactive nervous system and provide pain relief

• Our brains have these cells known as microglia which are like our brains’ security team. They get activated when there is nerve damage in the body and release signals that make the pain worse.

• Pain changes the central and peripheral nervous systems. Understanding this helps us better understand how to treat neuropathic pain.

Rosenberger, D. C., Blechschmidt, V., Timmerman, H., Wolff, A., & Treede, R. D. (2020). Challenges of neuropathic pain: focus on diabetic neuropathy. Journal of neural transmission (Vienna, Austria : 1996), 127(4), 589–624. https://doi.org/10.1007/s00702-020-02145-7