Trigger Point Injections for Post-Mastectomy Pain Syndrome

Trigger Point Injections for Post-Mastectomy Pain Syndrome: A Double-Blind Randomized Controlled Trial With Intention-to-Treat Analysis

Post-Mastectomy Pain Syndrome (PMPS) is a chronic pain that persists for more than three months after a surgical breast procedure. It has 11-70% incidence in patients that underwent a breast surgery. It consists of mixed pain, frequently associated with myofascial pain, an specific type of muscular pain. Trigger point injections (TPI) are classically used for the treatment of myofascial pain in other painful conditions. However, there are no controlled trials assessing the efficacy of TPI in the treatment of PMPS. The intervention objective is to assess the efficacy of TPI in patients with PMPS, when associated with a comprehensive rehabilitation program and pain management.

INTRODUCTION: Post-Mastectomy Pain Syndrome (PMPS) is a chronic pain that persists for more than three months after a surgical breast procedure. It has 11-70% incidence in patients that underwent a breast surgery. It consists of mixed pain, frequently associated with myofascial pain. Trigger point injections (TPI) are classically used for the treatment of myofascial pain in other etiologies. However, there are no controlled trials assessing the efficacy of TPI in the treatment of PMPS OBJECTIVE: Assess the efficacy of TPI in patients with PMPS, when associated with a comprehensive rehabilitation program and pain management. METHODS: Double-blind randomized controlled trial with intention-to-treat analysis. Both groups will undergo standard of care delivered by Physiatrist blinded to group allocation. Active group will undergo TPI with 1% lidocaine in each identified trigger-point, weekly, for three consecutive weeks. Control group will undergo subcutaneous saline injection superficial to the same trigger points, with the same frequency and number of sessions. Primary outcome is the mean difference between groups for pain levels, as assessed by Visual Numeric Scale (VNS), from baseline to 3 months after the procedure. STATISTICAL ANALYSIS: Difference between groups at baseline, one and three months after injection, using Analysis of Covariance (ANCOVA) for the following outcomes: VNS; Presence of active trigger points, Pressure pain threshold (PPT); Short-Form McGill Pain Questionnaire (SF-MPQ); Neuropathic Pain Symptom Inventory (NPSI); Disabilities of the Arm, Shoulder and Hand Questionnaire (DASH); Range of motion (ROM) of affected shoulder, for abduction and external rotation; adverse events; use of pain medication. Total sample size is 120. Alpha=5%, power=80%.

Post-mastectomy Pain Syndrome, Myofascial Pain Syndrome, Trigger Point Pain, Myofascial, Breast Cancer

Double-blind randomized controlled trial comparing the efficacy of TPI + standard of care (ACTIVE) versus sham TPI + standard of care(PLACEBO), with an intention-to-treat analysis

Patients will be randomized as they enter the study (T0). Only one of the researchers will have access to the randomization list. The researcher responsible for the procedure will receive an email at the day of the first injection, informing of the participant's allocation group. The outcomes assessor, patient, attending Physiatrist and the Rehabilitation team will be blinded to the patient's allocation group until the end of the study. Only the researcher the performed the TPI, and the researcher responsible for the allocation list will have access to that information.

3 weekly sessions of TPI. Participants will undergo 1mL injections of 1% lidocaine in the muscles identified with either active or latent trigger points at the initial assessment. The same muscles will be injected at all procedures.

3 weekly sessions of subcutaneous saline injections. Participants will undergo 0.2mL subcutaneous saline injections superficial to the trigger points identified at initial assessment. The same superficial sites will be injected in all procedures.

1mL injections of 1% lidocaine in the muscles identified active trigger points at the day of intervention (pectoralis major, serratus anterior, levator scapulae, latissimus dorsi, infraspinatus).

0.2mL subcutaneous saline injections superficial to the muscles identified with active trigger points at the day of intervention (pectoralis major, serratus anterior, levator scapulae, latissimus dorsi, infraspinatus).

Patients in both groups will undergo standard of care rehabilitation delivered by a Physiatrist, which may include Physical Therapy, Occupational Therapy, Exercise Physiologist, Rehabilitation Nurse, Psychologist, as per Physiatrist's prescription. Both the comprehensive rehabilitation program and pain medications will continue to be managed by participant's Physiatrist, who will be blinded to patient's allocation. The researchers will be responsible for TPI and for data collection.

Mean difference of Pain between groups from baseline to 3 months(T3m), assessed by the Visual Numeric Scale (VNS, 0-10), in which higher scores represent higher pain intensity.

Number of active trigger-points in the assessed muscles (latissimus dorsi, levator scapulae, trapezius superior, infraspinatus, pectoralis major, serratus anterior). Mean difference between groups.

Number of active trigger-points in the assessed muscles (latissimus dorsi, levator scapulae, trapezius superior, infraspinatus, pectoralis major, serratus anterior). Mean difference between groups.

Pressure Pain Threshold (PPT) at bilateral latissimus dorsi, levator scapulae, trapezius superior, infraspinatus, pectoralis major, serratus anterior. Difference from baseline

Pressure Pain Threshold (PPT) at bilateral latissimus dorsi, levator scapulae, trapezius superior, infraspinatus, pectoralis major, serratus anterior. Difference from baseline

Mean difference of Pain between groups from baseline,assessed by the Visual Numeric Scale (VNS, 0-10), in which higher scores represent higher pain intensity.

Short-Form McGill Pain Questionnaire - total score, sensorial and affective scale. Mean difference between groups from baseline. Higher values represent higher pain intensity

Short-Form McGill Pain Questionnaire - total score, sensorial and affective scale. Mean difference between groups from baseline. Higher values represent higher pain intensity

Neuropathic Pain Symptom Inventory . Mean difference between groups from baseline. Higher values represent more symptoms of neuropathic pain.

Neuropathic Pain Symptom Inventory . Mean difference between groups from baseline. Higher values represent more symptoms of neuropathic pain.

Disabilities of the Arm, Shoulder and Hand Questionnaire (DASH). Mean difference between groups from baseline. Higher values represent lower functionality.

Disabilities of the Arm, Shoulder and Hand Questionnaire (DASH). Mean difference between groups from baseline. Higher values represent lower functionality.

Range of motion (ROM) of affected shoulder, for abduction and external rotation. Mean difference between groups from baseline.

Range of motion (ROM) of affected shoulder, for abduction and external rotation. Mean difference between groups from baseline.

Percentage of patients with at least 30% improvement of pain as per VAS scores (VAS30%). Mean difference between groups.

Percentage of patients with at least 30% improvement of pain as per VAS scores (VAS30%). Mean difference between groups.

Percentage of patients with at least 50% improvement of pain as per VAS scores (VAS30%). Mean difference between groups.

Percentage of patients with at least 50% improvement of pain as per VAS scores (VAS30%). Mean difference between groups.

Use of pain medication. Classified as "Increased", "Decreased", "Stable" or "Non-applicable" . Mean difference between groups.

Use of pain medication. Classified as "Increased", "Decreased", "Stable" or "Non-applicable" . Mean difference between groups.

Inclusion Criteria: Breast cancer patients. PMPS diagnosis, as per Wisotzky et col. Pain > 3 months over breast, chest wall or shoulder ipsilateral to surgery. Pain Visual analog Scale (VAS) ≥4. At least one active trigger point in the following muscles: pectoralis major, superior trapezius, serratus anterior, levator scapularis, latissimus dorsi, infraspinatus Exclusion Criteria: Current radiation therapy or time since completion < 3months. Allergy to lidocaine or other local anesthetics Active infection over injection sites Unavailability to be at the hospital during study intervention.

Wisotzky E, Hanrahan N, Lione TP, Maltser S. Deconstructing Postmastectomy Syndrome: Implications for Physiatric Management. Phys Med Rehabil Clin N Am. 2017 Feb;28(1):153-169. doi: 10.1016/j.pmr.2016.09.003.