Thermography and sciatica: assessment from proximal to distal
Thermography allows identifying the consequences of different conditions, such as sciatica pain. This is due to its close relationship with the thermal patterns that it causes as it is a musculoskeletal pathology that implies a nervous compromise.
Sciatica pain, by definition, is an affectation of the sciatic nerve that produces a sensation of constant pain in the buttock, which worsens when sitting down. In addition, it can radiate throughout its course, and usually affects only one side of the body. Anatomically, the sciatic nerve is the longest in the human body, since it links from the lower back and runs through the lower limb in its posterior part.
The etiology of sciatica can be mechanical or muscular. Mechanical sciatica is caused by compression of the nerve root due to a herniated disc, a bone spur, spinal stenosis, etc. On the other hand, sciatica of muscular origin, known as piriformis syndrome or false sciatica, is due to compression of the nerve along the piriformis muscle, usually due to a local increase in the muscle tone.
Both cases have very similar symptoms, but from a thermographic point of view there are certain considerations that must be taken into account. Nerve involvement due to mechanical problems in the lower back area presents thermal patterns that are different from the muscular problems of piriformis syndrome.
Thermography has proven its usefulness in supporting the diagnosis of multiple pathologies according to their thermographic pattern. In the past, we have already seen clinical cases of spinal pathology, such as radiculopathy or lumbar surgery. In addition, we have already explored the different pathologies that are most commonly seen in clinical cases of back pain, from the point of view of thermography.
Scientific research shows us that for lesions that have nerve involvement, the typical pattern is hypothermia (see this publication for further understanding) due to a decrease in autonomic activation of the region (Dimitrijevic et al. 2016; Sillero-Quintana et al. 2015; Tuzgen et al. 2010; Green, 1987).
In cases of sciatica, what the evidence shows us is that the affectation occurs in the entire nerve root, harming the affected leg in its posterior view, decreasing the temperature. There has been thermography research on this effect on sciatica pain since the 1980s (Gillström, 1985), as can be seen in Figure 1:
Thermal patterns in the etiology of sciatica pain
We usually find island or blockage patterns in lumbar spine pathology. If there is radiation to one of the legs, the typical case of sciatica, we will find a lower temperature on the affected side compared to the healthy side and a characteristic pattern in the plantar area, which corresponds to the typical signs at the distal.
In the plantar area, the evidence shows us a pattern related initially to vasomotor disorders for those subjects with pain in the lower limb who present with symptoms of sciatica and after an operation with clear hypothermia (Zaproudina et al. 2006), as we can see in Figure 2:
In addition, this type of pathology with a mechanical etiology usually exalts the hypothermic response with movement, as is the case in the research carried out by Kim et al. (2018). It shows a decrease in temperature between 0.6 and 2.3 ºC after walking 10 minutes for patients with spinal stenosis, probably due to venous congestion, which causes neurogenic claudication, according to the authors (see figure 3):
On the other hand, if the affectation has to do with a muscular cause in the gluteal region, a higher temperature may occur due to the increase in work demand. On the other hand, it is common to find a pattern very similar to that caused by the mechanical etiology in the course of nerve entrapment. In figure 4, we show several case studies of Francisco José Soto, a student of the ThermoHuman certified course:
Case study: support for the diagnosis and follow-up of sciatica pain due to mechanical causes.
Below, we present a case study of a 36-year-old patient with previous evaluations of sciatica symptoms, who begins to suspect a mechanical problem at his low back. Subsequently, the existence of protrusions at the L4-L5-S1 level was confirmed by an MRI (Figure 5). From that moment on, the control of the pathology becomes relevant during the algesia processes through the application of thermography in the follow-up of the lesions.
For the injury follow-up, not only are the temperatures of the lower limb relevant and representative, but the plantar area must also be evaluated, as seen in previous paragraphs, to see how vasomotor disorders affect the plantar vision of the image. In figure 6, we have the example of our case study with the monitoring of their plantar temperatures during the first period of acute sciatica pain and the subsequent diagnosis. It is a fact similar to that described by Zaproudina et al. (2006):
In relation to the thermograms of the subsequent protocol, the temperature difference for the affected side (left, hypothermic) increases in relation to the symptoms. In the first image of figure 7, we observe the first episode where the pain was 2/10 on the VAS scale. In the second image, we can observe the day when the MRI was performed, which corresponds to 4/10 on the VAS scale, demonstrating a clear relationship between pain and asymmetry.
Thermography demonstrates its usefulness in the control and monitoring of sciatica or sciatic pain processes, regardless of its etiology, due to the hypothermic behavior of the pathology.
Temperature monitoring does not have to be evaluated only in the posterior view, but plantar view will also be of great help in the diagnosis support of this pathology.
Due to its speed, reliability and non-invasive nature, thermography has become a very useful tool in monitoring sciatica with the aim of restoring the normothermic state of athletes.
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Kim, T. S., Hur, J. W., Ko, S. J., Shin, J. K., & Park, J. Y. (2018). Thermographic Findings in Patients with Lumbar Spinal Stenosis Before and After Walking. Asian Journal of Pain, 4(2), 25-28.
Sillero-Quintana M, Fernández-Jaén T, Fernández-Cuevas I, Gómez-Carmona PM, Arnaiz-Lastras J, Pérez MD, Guillén P. Infrared Thermography as a Support Tool for Screening and Early Diagnosis in Emergencies. Journal of Medical Imaging and Health Informatics. 2015;5(6):1223-8.
Tuzgen S, Dursun S, Abuzayed B. Electrical skin resistance and thermal findings in patients with lumbar disc herniation. J Clin Neurophysiol. 2010 Aug;27(4):303-7.
Zaproudina N, Ming Z, Hänninen OO. Plantar infrared thermography measurements and low back pain intensity. J Manipulative Physiol Ther. 2006 Mar-Apr;29(3):219-23.
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