Opinion – Luciano Melo: Immunity and chronic low back pain

Arnaldo, if he had a little more energy, would be an activist for inactivity, but he preferred to pursue his bureaucratic career instead of facing such a paradox. Working seated, he executed a silent manifesto against movement. Armando is different, he carried sacks of cement for over a decade. Last year he changed jobs in order to get better pay. If it weren’t for a sick leave, he’d be operating a jackhammer.

Arnaldo and Armando, although different, are not similar only in name, both suffer from a continuous low back pain, radiating in shock to the right leg.

Before continuing with the subject, I make a brief caveat: I do not write here about serious causes of back pain, eventually fatal, whose symptoms may resemble those described here.

Many people, owners of lives and bodies similar to those of Arnaldo and Armando, will not face this chronic problem, since a sedentary lifestyle and continuous exposure to mechanical stress, combined or not, are not the only causes of common low back pain.

Other elements for this course are impactful, such as psychological profile, social conditions, biomechanical characteristics and genetic factors. However, we will not always be able to understand why one person suffers, while another, with similar biotype and occupation, does not. It doesn’t even matter if they have analogous changes seen in spine resonance.

Fortunately, new findings shed light on this matter, and the response that lights up blames the immune system.

To explain, I will return to the examples of Arnaldo and Armando, but I will go to the beginning, when the pain trigger was fired. The routines of the two men overloaded and deformed the structures of the lumbar spine, through which the sciatic nerve root passes. Pain radiating to the leg is a clinical sign that this root is, at least partially, strangled.

This constant insult profoundly modifies the entire neural system in charge of conveying sensitivity information from the leg to the brain — these changes are enhanced by a robust immune response.

The purpose of the immune system’s action within the damaged root is to cleanse what was so damaged that it was useless. However, immune action causes inflammation, and inflammatory activity causes more pain. Because it excites the still operational nervous structures to transmit more pain impulses.

In this way, the specific part of the brain responsible for receiving information from the sciatic root is flooded with an intense flow of pain data and, very curiously, it also becomes inflamed. Immune system cells are recruited to these inflamed brain areas, and other brain components are modified.

All these biological actions are important for the maintenance of brain function as they restore balance after any disturbance. However, its exaggerated activation is a threat and is involved in the transformation of acute pain into continuous pain. And chronic pain can persist even after your trigger has healed or healed. For this, it is enough for inflammation to persist, due to a failure of its balance, the body’s anti-inflammatory mechanisms.

Acute pain protects us, for it compels us to turn away from what is harmful. On the other hand, chronic pain does not have a clear beneficial function, it is essentially suffering. With an aggravating factor, it is difficult to remedy this symptom. The discovery of the role of the immune system in the perpetuation of pain brings hope for more efficient therapies, a lack of current medicine.

References:

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2. Alshelh Z, Brusaferri L, Saha A, Morrissey E, Knight P, Kim M, et al. Neuroimmune signatures in chronic low back pain subtypes. Brain. 2022 Mar 1;145(3):1098–110.
3. Miyamoto K, Kume K, Ohsawa M. Role of microglia in mechanical allodynia in the anterior cingulate cortex. J Pharmacol Sci. 2017 Jul 1;134(3):158–65.
4. Li T, Chen X, Zhang C, Zhang Y, Yao W. An update on reactive astrocytes in chronic pain. J Neuroinflammation. 2019 Jul 9;16(1):140.
5. Hartvigsen J, Hancock MJ, Kongsted A, Louw Q, Ferreira ML, Genevay S, et al. What low back pain is and why we need to pay attention. The Lancet. 2018 Jun 9;391(10137):2356–67.