Radiculopathy is known as the pathology that produces a decrease or loss of the sensory and/or motor function of a nerve root. Lumbar radiculopathy is the most common, but not the only one. Today we will see a review of this lesion in different populations and we will show how to learn to detect it with thermography.
Starting with the oldest literature on the matter, there are some individual studies (Hoffman et al., 1991; So et al., 1990) that indicate that thermography cannot be recommended as an exclusive diagnosis of peripheral neurology pathologies. However, some others are more favorable and indicate that thermography has proven efficacy in the detection of root pathologies (LaBorde, 1989) and that as a complementary tool with other tests, has a success of 82% (Green et al., 1986), which gives hope for its use with clinical purposes. This same research group, the following year (Green et al., 1987), published results in which they found a lower temperature on the side affected by radiculopathy (-1º C, hypothermia), but in the description of the case they said that the temperature of the area increased, so it seems that at that time the thermal behavior of a neurovascular injury was not very clear.
In image 1, belonging to the same study (Green, 1987), an image of a patient affected by neck pain and a peripheral nerve injury (radiculopathy, left arm) is shown in which, after quantitative analysis, an asymmetry of -1º C is observed, hypothesizing that the neurovascular pathology has a hypothermic behavior.
Image 1. Thermogram quantitatively analyzed, showing that the affected side (left) of a patient with radiculopathy has a hypothermic behavior (-1º C), compared with the healthy side (Green, 1987).
On the other hand, authors such as Aminoff et al. (1990), suggested that a hyperthermic behavior is expected in acute nerve injury, which turns into hypothermic as it becomes chronic, without adding data at any time to certify these assertions.
The strongest hypothesis seems to point precisely to the fact that this pathology is eminently cold, since the vast majority of published case studies agree in it. At the end of the nineties, we find a study (Zhang et al., 1999) in which patients with cervical hernias are presented, showing data of lower temperature in the entire affected territory than in the contralateral, as we can see in image 2.
Image 2. Patient with cervical hernia and irradiation to the right arm, showing a lower temperature throughout the affected territory (Zhang et al., 1999).
In the study of Tuzgen et al. (2010), the results of 15 lumbar radiculopathy patients with pain referred to one leg are shown, the affected side being colder and with greater resistance to electrical passage. These results seem to be confirmed by studies such as those of Dimitrijevic et al. (2016), where the affected side is cold and the greater asymmetry, the greater pain and less functionality, as we can see in image 3.
Image 3. Graphics from Dimitrijevic's study et al. (2016), showing that in a patient with lumbar radiculopathy, more asymmetry with respect to the healthy side implies greater pain, both at rest and during activity, and a worse score on a functionality scale (ODI).
Other case studies provide information on a collection of cases, where when it comes to nerve pathology they always show a lower temperature, such as the examples that we can see in Gillström (1985), Tokan (2004), Hildebrandt et al. (2010) and Sillero, et al. (2015), shown in image 4.
Image 4. Where we can see patients with nervous pathology and lower temperature of the affected region, corresponding to Tokan (2004) on the left and Hildebrandt (2010) on the right.
Regarding the precision of thermography in this type of pathology, according to the study by Takahashi et al. (1994), when the region was hypothermic, there was pain, hyposensitivity and hypomotricity in a 60.9, 69.3 and 71.8% of the cases, respectively, resulting in a sensitivity of 30% and a specificity of 80%. Other authors, such as Harper et al. (1991), establish these values between 78-94% for sensitivity and 20-44% for specificity.
Of the total number of patients studied, according to the studies that have investigated the thermal response of radiculopathy, the vast majority experience a decrease in temperature in the affected region. It is not at all negligible that there is a small percentage of cases, where the response is hyperthermic or neutral. Table 1 summarizes the results of the studies found that investigated in this regard (TY Park et al., 2020; ES Park et al., 1994; Ra et al., 2013). Nowadays, we cannot give an explanation, but it probably has to do with the coexistence of two or more pathologies of a different thermal nature. Example: a vertebral fracture. The bone behaves by increasing the temperature of the region because of the fracture, however, the interruption of the nerve root decreases it. The result is the sum of both outputs.
AuthorTotal of patientsHypothermic behaviorHyperthermic behaviorNeutral behaviorHypothermic behavior (%)Hyperthermic behavior (%)Neutral behavior (%)Park, 20202241804480.4%19.6%0.0%Park, 199421163276.2%14.3%9.5%Ra, 20137871791.0%9.0%0.0%Mean82.5%14.3%3.2%Table 1. Summary table of the thermal behaviors of radiculopathy patients. A large majority of hypothermic behaviors (82.5%) can be seen, ahead of hyperthermic (14.3%) or neutral (3.2%).
As we saw in this clinical case, if the lumbar pathology affects one of the limbs, it has a hypothermic profile on the affected side with compared to the healthy side. Today we will explain the case of a patient who, after a period of acute low back pain, began to feel a radiating pain in her right leg to the point of being considered disabling. After a MRI scan, a right posterolateral hernia was confirmed at the level of L4-L5. Ultimately, the surgeon decided on a hernia removal. During the operation, for an unknown reason some of the the nerve roots were probably compressed from the L3-L4 level. When she woke up, she immediately noticed a loss of sensation and motor skills in the right leg, especially in the posterolateral aspect of the leg and in the ankle and foot.
We proceeded to perform a thermographic analysis and the results speak for themselves. Image 5 shows the thermograms of the patient, the avatars representing the asymmetries, as well as the summary table of thermal data for the regions of the lower limbs and soles of the feet.
Image 5. Thermograms and avatars of a patient with severe radiculopathy. We can see that almost all the regions of the territories that are innervated from L3 to L5 have evident hypothermia on the affected side (right).
The results are presented below:
According to our clinical experience, whenever a patient affected by a neurovascular disease has acute symptoms (radiating pain, hyposensitivity and/or hypomotricity), the thermographic clinical sign will be a hypothermic asymmetry in the affected territory. The scientific literature to date agrees with this conclusion, but with a relative margin of error. In the patient's case, since she has a severe radiculopathy, the correlation between the symptoms and the thermal sign is practically perfect, where the regions with lower motricity or sensitivity are the coldest. In less severe patients, these findings are less obvious, although of the same nature.
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Dimitrijevic, I. M., Kocic, M. N., Lazovic, M. P., Mancic, D. D., Marinkovic, O. K., & Zlatanovic, D. S. (2016). Correlation of thermal deficit with clinical parameters and functional status in patients with unilateral lumbosacral radiculopathy. Hong Kong Medical Journal. Xianggang Yi Xue Za Zhi, 22(4), 320-326.
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Zhang, H. Y., Kim, Y. S., & Cho, Y. E. (1999). Thermatomal changes in cervical disc herniations. Yonsei Medical Journal, 40(5), 401-412.
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ThermoHuman has had the support of the Funds of the European Union and the Community of Madrid through the Operational Programme on Youth Employment. Likewise, ThermoHuman within the framework of the Export Initiation Program of ICEX NEXT, had the support of ICEX and the co-financing of the European Regional Development Fund (ERDF).
Thermohuman has received funding from the Centre for the Development of Industrial Technology (CDTI), in participation with the European Regional Development Fund (ERDF), for the R+D activities involved in creating a new tool, based on thermography, for the prediction and prevention of rheumatoid arthritis. See project detail.
