Exploring the efficacy of topical lidocaine in individuals with chronic neck pain

In a recent preprint study posted in Preprints with The Lancet, a team of researchers investigated the efficacy of lidocaine for the treatment of neck pain and assessed the need for additional research in this area.

*Important notice: SSRN publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Background

According to the 2015 Global Burden of Disease Study, neck and back pain were the leading causes of disability, with neck pain accounting for 44% of cases. Studies have shown that neck pain has a point prevalence of 3.6% and an annual incidence of 8.1%.

The neck experiences greater stress on musculature and facet joints than the lower back. Soft tissues play a significant role in neck pain, as evidenced by the effectiveness of topical nonsteroidal anti-inflammatory drugs and muscle relaxants.

Topical lidocaine has shown promise in relieving myofascial neck pain. The use of topical medications is particularly appealing for populations like the elderly and athletes due to limited side effects and drug interactions.

Recently a new formulation of lidocaine patch was approved in the United States for treating postherpetic neuralgia. This study hypothesized that this patch could improve treatment outcomes for mechanical neck pain.

About the study

In the present study, researchers recruited participants from various institutions, including a teaching hospital, military treatment facility, urban veterans’ administration hospital, and private practice. The age of participants was between 18 and 90 years old and had experienced axial neck pain for more than 3 months.

They had reported an average neck pain score higher than 4 out of 10 in the week before enrolment and demonstrated tenderness to palpation in specific areas. Patients with specific medical conditions like pregnancy or skin defects over painful areas were excluded.

The study employed a randomized, placebo-controlled crossover design with two treatment groups. Lidocaine patches with enhanced bioavailability were used, along with identical placebo patches. Participants received one to three patches based on their pain extent.

Data collection included baseline information, pain scores, functional measures, sleep quality, and other assessments. Follow-ups were conducted at 4-week intervals, statistical analyses were performed, and adjustments were made due to coronavirus disease 2019 (COVID-19)-related disruptions.

Study results

The results of the study showed that out of the 76 patients recruited in this study, 60 completed both the lidocaine and placebo patch phases, while 12 completed only one phase (seven in the placebo patch group and five in the lidocaine patch group).

There were no significant differences in demographics or baseline outcome measures between the two treatment groups. The primary outcome measure, which was the reduction in average neck pain score, showed no significant difference between the two groups. Similarly, the average neck pain score at the end of treatment was also not significantly different in the lidocaine patch group.

The researchers further reported that the percentage of patients who had a successful outcome, defined as a 2-point or greater reduction in average neck pain coupled with a score greater than 5 on the patient global impression of change (PGIC) scale, was 27.7% in the lidocaine patch group compared to 14.9% in the placebo patch group.

Secondary outcome measures, such as reduction in worst neck pain score and change in Neck Disability Index (NDI), did not show statistically significant differences between the groups.

Adverse events were reported by 27.5% of patients in the lidocaine patch group compared to 20.5% in the placebo patch group. The most common complication in both groups was pruritus, experienced by 9.0% of patients in the placebo phase and 9.2% in the lidocaine phase.

In terms of blinding effectiveness, 58.3% of patients correctly guessed the sequence of their treatment. The James Blinding Index, which measures blinding effectiveness, was 0.77, indicating that blinding was generally effective in the study.

Implications

The main findings of the study showed that there were no significant differences between lidocaine and placebo patches in terms of reducing average neck pain scores. The results were less favorable than some studies that showed a significant effect of lidocaine.

The lack of significant difference may be attributed to factors such as poor penetrance and adherence to previous lidocaine patches. However, the study did find a higher, although still low, success rate associated with lidocaine patches compared to placebo.

The authors discussed the possibility that both skin and muscles can be pain generators in the body. The depth of the musculature in the neck, which is comparable to the penetrance of the lidocaine patches used in the study, may explain the potential effectiveness of lidocaine for neck pain. However, it is important to note that myofascial pain often co-occurs with spine pathology that may not respond to topical therapies.

In subgroup analyses, it was found that a shorter duration of neck pain and lower baseline NDI scores were associated with a higher likelihood of positive treatment outcomes. This suggests that individuals with less disease burden may respond better to lidocaine treatment. Younger age was also associated with a positive treatment outcome, potentially due to the higher contribution of myofascial pain in younger individuals.

In conclusion, while there were slight improvements in neck pain observed with lidocaine in the most important measures, the differences were not statistically significant. This highlights the need for further research to evaluate products with higher dosing and penetrance and to apply more stringent selection criteria based on phenotyping. Additional studies are necessary to determine if these modifications can lead to more significant outcomes.

*Important notice: SSRN publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Written by

Vijay Kumar Malesu

Vijay holds a Ph.D. in Biotechnology and possesses a deep passion for microbiology. His academic journey has allowed him to delve deeper into understanding the intricate world of microorganisms. Through his research and studies, he has gained expertise in various aspects of microbiology, which includes microbial genetics, microbial physiology, and microbial ecology. Vijay has six years of scientific research experience at renowned research institutes such as the Indian Council for Agricultural Research and KIIT University. He has worked on diverse projects in microbiology, biopolymers, and drug delivery. His contributions to these areas have provided him with a comprehensive understanding of the subject matter and the ability to tackle complex research challenges.