Complex regional pain syndrome: the use of thermography to assess treatment.

Victor Escamilla


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Complex regional pain syndrome: the use of thermography to assess treatment.
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Complex regional pain syndrome (CRPS) is a pathology that is characterized by chronic pain that appears spontaneously or provoked after having suffered some previous trauma or injury and that affects the sensorimotor, vasomotor, or sudo-motor system.

Complex regional pain syndrome is generally triggered after fractures, sprains, or surgeries and most frequently affects the extremities (Marinus et al 2011). Because of this, people in factories suffer from CRPS almost twice as often as people in other occupations, possibly due to the physical activity associated with the job (Allen G et al. 1999). The incidence of CRPS is estimated between 5.46 and 26.2 per-100,000 people.

The alteration of the sympathetic nervous system seems to be the main one implicated in CRPS (Bruehl, S. et al. 2010) and some symptoms that patients present in the affected limb, such as edema and changes in skin texture or sweating, seem to be compatible with a dysfunction of the autonomic nervous system (Birklen, F et al 2017). Therefore, achieving pain suppression through anesthetic strategies, such as sympathetic nerve block, are a widely performed procedure in the treatment of CRPS, as it can reduce some of the symptoms and alleviate pain (Day, M et al. 2008).

For example, lumbar sympathetic block (LSB) is performed by local injection of an anesthetic drug (such as bupivacaine, lidocaine, or ropivacaine) around the lumbar sympathetic ganglia between the L2 and L4 lumbar vertebral levels of the affected limb.

Due to all these factors, thermography has been postulated as a useful tool to assess the efficacy of treatment and the evolution of its prognosis. That is why Cañada-Soriano, M. et al. (2021) in a preliminary study carried out and later in the thesis published on the same topic (2022) wondered what the effects and thermal response would be after a lumbar sympathetic block.

Preliminary analysis of patients with Complex Regional Pain Syndrome (CRPS).

When the LSB is performed, the innervation is interrupted and changes in blood flow occur in the distal parts of the extremities, such as the feet (Qian, S. et al. 2019). For this reason, skin temperature monitoring is used as an indicator of the success of sympathetic blockade (Borchers, A.T et al 2017).

For the LSB to be considered successful, there must be changes in the ipsilateral limb temperature of up to ≥2ºC between the two moments. In the past, common clinical practice for assessing temperature involved manual palpation of the foot. However, temperature changes are often too small to assess temperature in various parts of the foot (Gatt, A et al 2015). Furthermore, there are several drawbacks to using conventional methods, so thermography seems to be the best tool for this purpose.

Until the study by Cañada-Soriano et al. (2021) there was no precedent in the literature for the utility of thermography to assess its utility. Therefore, these authors wanted to analyze the temperature data of the plantar foot skin acquired during the performance of lumbar sympathetic blocks in patients with CRPS.

Study results in patients with complex regional pain syndrome.

Forty-four lumbar sympathetic blocks (LBS) were performed for the treatment of CRPS in 13 patients (7 men - 6 women) aged 41 ± 7 years. For each patient, three specialist appointments were scheduled to perform 3 lumbar sympathetic blocks, approximately 2 weeks apart between each puncture. (Figure 1)


Figure 1. Treatment using a sympathetic lumbar block.

Once the needle was positioned, the thermal response of the sole of the foot was awaited; if it occurred in the first 4 minutes, it was considered successful. Whereas, if no change was produced, the needle was removed and repositioned again, considering it failed.

The device used to assess skin temperature was a FLIR E60 thermal camera (FLIR Systems, Inc.Wilsonville, OR) with an infrared resolution of 320 × 240 pixels. In addition, 11 regions of the foot were analyzed to assess skin temperature. temperature evolution. (Figure 2)


Figure 2. Selection of regions of interest to analyze the change after blocking.

The results showed that from the third minute onwards the blood flow of the foot increased in the cases where the maneuver had been successful, consequently increasing the temperature of the foot regions. These changes had two types of responses depending on the variability of the individual.

On the one hand, some individuals only increased in temperature in the ipsilateral region where they had received the puncture. On the other hand, some participants increased their temperature bilaterally, which was also synonymous with treatment success.

Lastly, as explained in the methodology, if there was no response 4 minutes after needle placement, then the treatment was considered unsuccessful, and the needle was repositioned. (Figure 3.)


Figura 3. Main thermography results.

Conclusions of the preliminary study and the Results of the subsequent doctoral thesis.

The use of real-time infrared thermography allowed medical personnel to determine whether the LSB injections performed were successful. Only 32% of the cases did not register temperature variations after the lidocaine injection, which made it necessary to relocate the position of the needle. For successful cases, after lidocaine injection, increases in foot skin temperature were observed starting at 420 s for the mean temperature of the region.

These results led to the doctoral thesis of Cañada-Soriano et al (2022) where they evaluated which of the regions was the most responsive, noting that the heel region, and especially the average and maximum asymmetry in that region, are the ones that contribute the most to detect the efficacy of the treatment.


Cañada-Soriano M, Priego-Quesada JI, Bovaira M, García-Vitoria C, Salvador Palmer R, Cibrián Ortiz de Anda R, Moratal D. Quantitative Analysis of Real-Time Infrared Thermography for the Assessment of Lumbar Sympathetic Blocks: A Preliminary Study. Sensors (Basel). 2021 May 21;21(11):3573. doi: 10.3390/s21113573.

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