The transcutaneous electrical nerve stimulation of variable frequency intensity has a longer-lasting analgesic action than the burst transcutaneous electrical nerve stimulation in cancer pain

BACKGROUND AND OBJECTIVES: Pain is one of the most frequent symptoms in cancer, and physical therapy offers non-invasive methods such as the transcutaneous electrical nerve stimulation for the relief of symptoms. The objective of this study was to compare the effect of the burst transcutaneous electrical nerve stimulation with the transcutaneous electrical nerve stimulation with variable intensity frequency in cancer pain. METHODS: This study was conducted with 53 patients of the Hospital Erasto Gaertner, divided into two groups: burst transcutaneous electrical nerve stimulation and variable intensity frequency transcutaneous electrical nerve stimulation. Pain assessment was performed before and right after the electroanalgesia, and at every hour until completing 6 hours. RESULTS: The group treated with burst transcutaneous electrical nerve stimulation maintained complete analgesia for 2 hours, returning to the initial score value within 6 hours of evaluation; the group of variable intensity frequency transcutaneous electrical nerve stimulation maintained complete analgesia for 4 hours, not returning to the initial score value within the 6 hours. When comparing the intensity of the pain between the groups there was a significant difference between them (p<0.001) in all the assessments from the third hour after the electroanalgesia, showing a significant difference (p<0.001) at the 3rd and 4th hour after the electroanalgesia. There was no difference at the 5th hour and at the 6th hour. CONCLUSION: The variable intensity frequency transcutaneous electrical nerve stimulation provided a longer-lasting analgeThe transcutaneous electrical nerve stimulation of variable frequency intensity has a longer-lasting analgesic action than the burst transcutaneous electrical nerve stimulation in cancer pain Estimulação elétrica nervosa transcutânea de intensidade e frequência variável tem ação analgésica mais duradoura que a estimulação elétrica nervosa transcutânea burst sobre a dor oncológica Juliana Carvalho Schleder1, Fernanda Aparecida Verner2, Loriane Mauda3, Débora Melo Mazzo4, Luiz Cláudio Fernandes5 1. Universidade Federal do Paraná, Hospital Universitário Regional dos Campos Gerais, Departamento de Fisioterapia, Ponta Grossa, PR, Brasil. 2. Hospital Cajuru, Departamento de Fisioterapia, Curitiba, PR, Brasil. 3. Pontifícia Universidade Católica do Paraná, Curso de Medicina, Curitiba, PR, Brasil. 4. Universidade Estadual de Ponta Grossa, Hospital Universitário Regional dos Campos Gerais, Departamento de Fisioterapia, Ponta Grossa, PR, Brasil. 5. Universidade Federal do Paraná, Departamento de Fisiologia, Curitiba, PR, Brasil. Submitted in May 10, 2017. Accepted for publication in October 30, 2017. Conflict of interests: none – Sponsoring sources: none Correspondence to: Rua Cruz e Souza no 430 ap. 11 – Jardim Carvalho 84015-420 Ponta Grossa, PR, Brasil E-mail: deboramazzo@uol.com.br © Sociedade Brasileira para o Estudo da Dor sia in cancer pain than the burst transcutaneous electrical nerve stimulation.


INTRODUCTION
The control of cancer pain is routinely done through the evaluation of the symptom, drug administration, and surgical treat-ORIGINAL ARTICLE DOI 10.5935/1806-0013.20170122The transcutaneous electrical nerve stimulation of variable frequency intensity has a longer-lasting analgesic action than the burst transcutaneous electrical nerve stimulation in cancer pain Rev Dor.São Paulo, 2017 oct-dec;18(4):316-20 ment.However, its treatment should not be restricted to these conventional approaches 1,2 .Among the several non-phamacological approaches, there is a physiotherapeutic modality called transcutaneous electrical nerve stimulation (TENS) 3 , that transmits electric current using electrodes located on the skin 2 .The current acts at the cellular level, exciting the peripheral nerve cells, causing the release of endogenous substances such as endorphins, enkephalins, and serotonin in the body 4 , that consequently will affect segmentary and systemic levels.Its main advantages are not overwhelming organs and systems since it does not need to be metabolized; low cost; easy to use; and few adverse effects 5.6 .Some studies confirm the effectiveness of TENS in cancer pain 4,7 .However, patients tend to adapt themselves to the sensitivity of the continuous stimulaton 6,8 .In the face of this came the questioning if variations in the form of the transcutaneous electrical stimulation, as it occurs in TENS with variable intensity and frequency (VIF), would present better results in pain relief since the tendency to adaptation is lower.Thus, the objective of this study was to investigate which modality has a better beneficial effect on cancer pain: TENS with modulated pulses (burst) or TENS VIF.

METHODS
This is a prospective, applied, experimental and quantitative study conducted at Hospital Erasto Gaertner (HEG).The sample was collected in a directed form for convenience, and the patients included in the study were hospitalized to undergo chemotherapy and/or radiotherapy, of both gender, who had a physiotherapy prescription, and that reported cancer-related pain.
Patients below 18 years old with a complaint of pain not related to cancer were excluded from the sample.The size of the sample was estimated in a number higher than 20% of the population who had a prescription for physiotherapy during hospitalization, and that reported pain since this size is enough to represent the population.However, after the previous evaluation of the patients, the size of the sample was bigger, totalizing 73% of the evaluated patients.Before starting the evaluation procedures and the current application, the patient signed the Free and Informed Consent Form (FICT).The initial evaluation, made by researcher 1, consisted of collecting information inherent to the patient's characteristics, type of cancer and the pain symptom.To evaluate pain characteristics, we used the McGill Pain Questionnaire, translated and adapted to the Portuguese language in 1996 by Pimenta and Teixeira 9 , and the multidimensional pain evaluation scale (EMADOR) 10 , that consists of a numerical scale (NS) from 1 to 10; the higher the numerical value, the higher is the pain reported by the patient; descriptors referring to the types of pain -acute or chronic; and an illustration of the body to register the site of pain.
After that, the patient raffled off the current that would be applied, without knowing which current it would be.The single application was made by a physiotherapist (Researcher 2) using the HTM ® TENS-FES device portable, with burst parameters and pre-programmed VIF with maximum intensity tolerated by the patient, with duration of 40 minutes.In case the patient reported pain in more than two sites, the electrodes were placed on the site with higher reported pain, being related to cancer.The pain revaluation, made by Researcher 1, who did not know the applied current, was done right after the removal of the device, and at every hour until completing 6 hours.Self-programmed by device, repetition frequency with automatic variation increasing from 10 to 200Hz and decreasing from 200 to 10Hz; pulse width with automatic variation, increasing from 60 to 180μs, decreasing from 180 to 60μs 16 ; current's intensity within the limit considered tolerable by the patient, generating muscular contractions 15 .
Electroanalgesia was maintained for 40 minutes.After the time had run out, the current's intensity was reduced to zero.Only then did the appliance shut down.
After the electrodes were removed, a new asepsis was performed with hydrated ethylic alcohol at 70% and paper towel to remove excess gel used during the procedure and the inspection of the application area was performed.
Pain reassessment, performed shortly after the electroanalgesia application, and once every hour, until completing 6 hours after the application.

Evaluated (n=73)
TENS BURST (n=28) Low frequency of 2 Hz, pulse width of 180μs, current's intensity within the limit considered tolerable by the patient, generating muscular contractions 15 .

Statistical analysis
It was found that the sample did not follow the Gaussian distribution with the Kolmogorov-Smirnov test.Non-parametric Wilcoxon tests were used for the descriptive analysis of the data to check the difference between the evaluation before applying TENS and all the other evaluations of the same group; and the Mann-Whitney's U test to compare all evaluations between the groups.To better understand the treatment effect of each current, we calculated the differences in pain intensity rates at the fifth hour after the treatment and the necessary number to treat (NNT) to prevent any failures in the proposed treatment.To verify if there was an association between the pain classification identified by the patients and the electrotherapeutic resources applied, the Chi-square test was used.The significance level adopted for the statistical tests was 5% in a 95% confidence interval.

RESULTS
The burst group consisted of 13 male patients, and 15 female patients, the age of this group was 56.53±14.21years, with a minimum of 23 years and a maximum of 81 years.The VIF group consisted of 15 male patients and 10 female patients.The age was 53.16±12.78years, being 36 years the lower age and 83 years the highest.The neoplastic topography of the groups varied between lungs, breast, stomach, ovaries, liver, lymphatic system, face, and neck.
In burst group, 16 patients had a histological diagnosis of adenocarcinoma, 2 patients had lymphoma and 4, sarcoma, and 6 patients did not have such information in the medical record.In the VIF group, 14 patients had adenocarcinoma as histological diagnosis, 4 had lymphoma, 4 had sarcoma, and 3 patients did not have this information in their medical records.
Regarding the use of pain medication, all patients received analgesics, including anti-inflammatories or opioids.When evaluated by the EMADOR, the number of body sites that the patients reported pain in the burst group were n=10 (36%) at one site, n=15 (52%) at two sites and n=3 (12%) at three sites; and in the VIF group, n=5 (21%) had pain at one site, n=17 (69%) at two sites and n= 3 (10%) at three sites.
In the classification of the type of pain, in the burst group n=12 (42.86%) of the patients classified pain as chronic and n=16 (57.14%) as acute.The VIF group had n=9 (36%) of the patients with the symptoms classified as chronic and n=16 (64%) as acute.
In the assessment of pain before the electroanalgesia between the groups (Mann-Whitney U test), no significant differences were found, both in the McGill score (p=0.538), and in the numeric pain rating scale (p=0.536).Both groups presented severe pain according to the numeric pain scale.The comparison of the pain intensity reported by the patients and the score obtained with the McGill pain questionnaire between the pre-application evaluation of electroanalgesia and the post-application evaluations are described in table 1.
The intensity of the pain of the two groups, throughout the evaluations, is presented in figure 2.
As of the third hour after the application of the electroanalgesia, a significant difference was found in the VIF group (p<0.001versus burst) in all evaluations until reaching 6 hours.The McGill pain score of both groups throughout the assessments is shown in figure 3.

DISCUSSION
The neoplastic topographies found in the present study varied among different regions, as did the study by Salamonde et al. 11 who studied 93 patients and the location also referred to several sites as the lung, uterus, large intestine, breast, prostate, bone marrow, kidney, liver, stomach, pancreas and small intestine.Loh and Gulati 12 analyzed the use of TENS to improve the functionality of cancer patients, and the topography was also very diverse, predominating the breast cancer and sarcomas.Few studies have evaluated the action of TENS in a population with some specific type of cancer.Hurlow et al. 13 did a systematic review aiming to develop studies addressing the treatment of cancer pain in adults with the use of TENS, but only three   randomized controlled trials were included in the review, which evidences the lack of research on the subject.Most patients had pain in more than one site.This same result was reported by Pimenta, Koizumi and Teixeira 14 , who stated that every patient had reported pain in more than one site, averaging 1.8 different pain sites.The pain level of both groups was initially high.When comparing the pain and intensity scores before the electroanalgesia, both levels were similar.
A study 15 evaluated 8 patients with sarcoma-related pain who were treated with high-frequency TENS, and, as in the present study, the McGill questionnaire was used to quantify pain before and after the application.Among the 8 patients, 7 had satisfactory results regarding the reduction of pain besides the improvement in functionality, showing the clinical efficacy of TENS both in movement and at rest.In the comparison of the pain score and pain intensity between the groups, from the 3 rd to the 6 th hour after the electroanalgesia, there was a significant difference between them, that is, TENS VIF had a longer lasting analgesic effect than TENS burst.It is believed that this result occurred because in the TENS VIF it is established a minimum and maximum value and frequency, generating a variation of these values during the application.This function prevents, or at least delays, the onset of the accommodation effect 16 .In Loh and Gulati 12 retrospective study, the use of TENS was analyzed concerning the functionality improvement of 87 patients with different types of cancer, when the pain questionnaire was applied at the beginning of the treatment and two months later.At the end of two months of follow-up, 76 patients were evaluated, and among them, 69.7% reported benefits in the use of TENS, with improvement in pain and quality of life.Johnson et al. 17 conducted a systematic review of the effect of TENS in acute pain.There were 19 randomized clinical trials, and among these, only four have compared two active currents.The authors reported difficulties due to the lack of information on the intensity, extent, duration, and frequency of the treatment sessions.Most studies used standard questionnaires to quantify pain.However very few clarified the moment when those questionnaires were applied, which does matter when the goal is to compare the duration of the analgesic action of the current.
Although the present study and the others cited do present positive results about the reduction of cancer pain, yet there is no consensus on the use of TENS in these patients.However, there is an increasing interest in investigating its effect, since it has been used in the control of acute and chronic pain in this population 18,19 .Another important point is that few studies focus on the parameters adjusted in that current.Gopalkrishnan and Sluka 20 analyzed the effects of two frequencies (100Hz and 4Hz), two pulse widths (100μs and 250μs) and two intensities (motor and sensory), during 20 minutes, on hyperalgesia and induced inflammation in rats.In that study, to the surprise of the authors, only the frequency had relation with analgesia.It is worth mentioning that the parameters were fixed and did not vary as in our study.Based on the preceding, the use of electroanalgesia with TENS, with the parameters used, was effective in the treatment of cancer pain, since this type of intervention does not cause addiction and has no adverse effects 18,20 .

CONCLUSION
The use of TENS, with the used parameters, has efficiently reduced the cancer pain for at least 3 hours.The best results were found with the use of the TENS VIF current regarding analgesia duration compared to TENS_ burst.

Figure 1
details the study design.This study was approved by the Committee of Ethics in Research of the Hospital Erasto Gaertner (HEG) under number 2153nov/2011.

Figure 1 .
Figure 1.Details of the survey (attached file)

Figure 2 .
Figure 2. Pain intensity in both groups over the different evaluation moments *p<0.001versus VIF.

Figure 3 .
Figure 3. McGill pain score in both groups over the different evaluation moments *p<0.001versus VIF.

Table 1 .
Comparison of the pain intensity and pain score by the McGill questionnaire of all the evaluations of the referred scores before the application of the transcutaneous electrical nerve stimulation

Table 2 .
Frequency of pain rating reported by patients at the sixth hour after the electroanalgesia application