Introduction
Mastalgia refers to pain affecting one or both breasts (1). Nearly 80% of women experience breast pain at some point in their lives; yet the etiology of this pathology has not been fully elucidated (2). It has been reported that women with mastalgia complaints had moderate to severe pain and 11% of patients had mild pain. Mastalgia affects women’s social, physical, sexual, and work life (3-5). One-third of mastalgia patients are classified as cyclic, as in the menstrual cycle, and one-third of are non-cyclic (6,7). Cyclic mastalgia is especially severe in women during the reproductive period, and pain is usually bilateral. In a population-based survey, Ader et al. (6) found that 68% of women aged 18 to 44 experienced cyclic breast symptoms, and 22% of these rated their pain moderate to severe. Non-cyclic pain is not associated with menstrual cycle, often observed after menopause, usually unilateral and tends to be focal. This pain is often felt in the subareolar or medial half of the mammary gland (7).
The physiopathology of breast pain has not been fully elucidated. Elevated serum fatty acids, elevated basal prolactin levels, high-fat diet, smoking, and hormone replacement therapy are among the etiologic factors (8-14). Studies have shown that psychological factors also play a role in the etiology of mastalgia (15,16). In addition, pain in the mammary gland itself, as well as pathologic diseases in the muscles, joints and bones around the breast may also cause mastalgia. Pain caused by pain syndromes or rheumatological diseases that effects the adjacent body parts (shoulder, arm or ribs) may also be felt as breast pain (17,18).
In the literature, there have been studies suggesting a relationship between mastalgia and fibromyalgia that has been reported to affect 2.1%-10.5% of women (19-23). Electromyography (EMG) is one of the commonly used diagnostic methods for muscle and nervous system-related disorders such as fibromyalgia (24). The cutaneous silent period (CSP) is a useful tool for evaluating pain caused by the peripheral and central nervous system. CSP is an inhibitory spinal reflex which appears following strong electrical stimulation of a cutaneous nerve and causes suppression of voluntary muscle contraction for a certain period of time. The afferent arm of the CSP is formed by somatic small-diameter fibers. The CSP is a prospective electrophysiological method for the diagnosis of small fiber dysfunction. However, only a few studies have shown a relationship between CSP and fibromyalgia with chronic pain, and there are a limited number of studies evaluating the relationship between mastalgia and CSP (25-27).
In this study, we aimed to evaluate the relationship between pectoralis major (PM) muscle EMG measurements and mastalgia in patients with and without non-cyclic unilateral breast pain in order to elucidate the etiology of mastalgia.
Methods
This prospectively designed study started after the approval of the Şisli Hamidiye Etfal Education and Research Hospital Local Human Ethics Committee (no: NCT02784379). Mastalgia patients who were admitted to the breast surgery outpatient clinic at Şisli Hamidiye Etfal Education and Research Hospital between December 2015 and May 2016 comprised the study population. Inclusion criteria were 18-65 years of age, intermittent or continuous mastalgia complaints for at least 1 month, unilateral breast pain, and non-cyclic breast pain. Exclusion criteria included pregnancy, breastfeeding, breast surgery history, breast cancer history, cystic or solid lesion larger than 1 cm detected by mammography or ultrasonography (USG) suspected breast cancer, and orthopedic or neurological pathologies in the upper extremities, neck and thoracic region. Informed consent was obtained from all the patients included in the study, and a Clinical Trials application was completed at the beginning of the study (CT number: NCT02784379).
Data on patient age, family history, the number of children, age at menarche, body mass index (BMI), physical examination findings, and breast ultrasonography and mammography findings were recorded. Amplitude and latency measurements of the EMG (Viasys Healthcare, Synergy, Ireland) of the right and left PM muscle were noted. The EMG findings, motor distal latency and amplitudes of the PM muscle, CSP and spinal evoked potential (SEP) responses of the healthy and mastalgia sides of breasts were compared.
Electrophysiological Method
Concentric needle electromyography was performed on the deltoid, triceps, biceps, extender digitorum cominis, flexor carpi radialis, and 1st dorsal interosseus muscles, and measurements of the motor and sensory nerve conduction velocities and amplitudes of both upper extremities were performed on the basis of the pathologies that may lead to collar, shoulder and chest reflected sensory disturbances in all patients. As a result of these studies, patients with additional anomalies such as entrapment neuropathy and radiculopathy were not included in the study. After that, the following electrophysiological studies were carried out for mastalgia:
1) Needle electromyography of both PM muscles was performed
2) Recordings of superimposed electrical stimulation of the PM muscle by electrical stimulation of the PM muscle motor nerve from the Erb’s point were analyzed. In addition, the process was repeated with a needle electrode. The distal latency of the motor nerve response obtained by both techniques and the amplitudes of the compound muscle action potential obtained by superficial recording electrodes were compared between the two sides of the breasts.
3) The PM muscle was used for the CSP evaluation. The supraclavicular nerve was stimulated superficially to the posterior border of the sternocleidomastoid muscle at a distance of 6 cm from the sternoclavicular joint and recordings were obtained from the PM muscle via bar electrode. Before the recording, the patient was asked to perform shoulder adduction with maximal effort and the maximal motor unit potential (MUP) amplitude was measured on the screen. The subjects were asked to perform shoulder adduction with MUP amplitudes of at least 25% of the maximal MUP amplitude. While the patient was constantly performing this adduction, the supraclavicular nerve was stimulated at 80 mA intensity, sweeps of 250 ms and duration of 0.5 ms. Ten recordings were obtained at 30 second intervals. The CSP latency and duration were measured by assessing the average of 10 traces and compared between both sides of the breasts.
4) To evaluate wide-diameter fibers, superficial recording electrodes were placed on the PM muscle, and electrical stimulation of the axillary regions was performed. SEP response latencies of both sides of breasts were compared.
Statistical analysis
SPSS 21.0 (IBM Corp. Released 2012. IBM SPSS Statistics for Windows, Version 21.0. Armonk, NY: IBM Corp.) was used for statistical analysis. Descriptive statistics included mean, standard deviation, median, and quartile interval for numerical variables. Paired t-test was used to assess differences between numerical variables that conformed to a normal distribution condition, and the Wilcoxon sign test was used when normal distribution conditions were not met in the dependent group. The statistical significance level was set at p<0.05.
Results
Thirty-one patients with no USG and mammographic findings of mastalgia were enrolled in the study. The mean age of the patients was 43.3 (20-65) years; 22 patients (71%) had complaints of mastalgia in the left breast and nine (29%) in the right breast. Six (18.75%) patients had a family history of breast cancer. Twenty-three patients (74.1%) had a BMI of ≥25 kg/m2. A size difference was observed between the breasts in 11 patients, and in eight of these patients, the mammary gland with mastalgia was larger (Table 1).
The EMG results of the PM muscle in the healthy and mastalgia sides of the breast tissue in the same patient were compared. No statistically significant difference was detected in amplitude and latency parameters of the EMG measurements between the groups (p>0.05) (Table 2).
However, when the CSP of the right and left side PM muscle of the patients were evaluated, the CSP latency and duration on the mastalgia side was significantly longer compared with the non-mastalgia side (p=0.024).
Discussion
Mastalgia may be a symptom of many breast-related diseases, but mastalgia can also occur for many reasons in patients without breast diseases. Mastalgia can also be induced by disorders of the skeletal and muscular systems, particularly via the pain associated with the location of the costochondral component and lateral involvement of the anterior axillary line (28). Mastalgia can also affect quality of life. In their study including 1171 participants, Ader et al. (4) reported that mastalgia interfered with usual sexual activity in 48% of women and with physical, social and work or school (6%) activity in 37%, 12% and 6% of women, respectively.
The use of EMG to obtain information about muscle response or electrical activity to a nerve’s stimulation of a muscle provides information to the clinician regarding many conditions such as muscle aches, muscle weakness, anomalies related to muscle movements, and muscle atrophy (24,29). Although many studies have evaluated the relationship between fibromyalgia and the nociceptive flexion reflex, we did not find any study evaluating the relationship of nociceptive flexion reflex with mastalgia (30,31). Furthermore, only a few studies have evaluated the relationship between fibromyalgia and CSP, and we found no study investigating the relationship between mastalgia and CSP (25-27). Thus, our unique study was aimed at assessing EMG results in the PM muscle in the non-mastalgia and mastalgia sides of the breasts to determine whether unilateral mastalgia without organic breast disease is due to a muscle pathology.
Fibromyalgia and mastalgia share many similar features. For example, both are more prevalent in the female population, both are believed to develop due to stress, and both include clinical similarities (30,32). In their study including 50 patients with mastalgia and 50 with fibromyalgia, Genc et al. (31) reported that 36% of mastalgia patients met fibromyalgia criteria, and 42% of fibromyalgia patients had mastalgia complaints. In another study by Sen et al. (30), 47.2% of 53 patients with fibromyalgia had mastalgia and 37.7% of 61 patients with mastalgia met the diagnostic criteria for fibromyalgia syndrome (30).
Studies on the relationship between exercise and mastalgia have reported that the incidence of mastalgia during physical activity varied between 29% and 37% (3,4,33). In a study investigating mastalgia complaints seen in marathon runners, 32% of 1285 runners reported mastalgia. In this study, mastalgia increased with increasing breast size, body mass index and exercise amount, and no relationship with age was detected. Approximately 17% of the participants in the study reported that they had to change their exercise programs due to mastalgia (33). However, in these studies, no information was provided regarding whether mastalgia was caused by muscular anomalies related to exercise. In our study, complaints of mastalgia were present on the side of the larger breast in 8 patients who had different breast sizes.
Few studies in the literature have explored the relationship between fibromyalgia and CSP. Umay et al. (25) compared CSP latency and duration in upper and lower extremities between 32 patients with fibromyalgia and 32 healthy controls and found that both upper and lower extremity CSP latencies in the EMG activity were higher in fibromyalgia patients. Baek et al. (27) compared CSP patterns between 24 patients with fibromyalgia patients and 24 healthy volunteers and reported that CSP duration values in fibromyalgia patients were significantly higher compared with controls and that longer CSP duration in fibromyalgia patients suggested central dysregulation at the spinal and supraspinal levels rather than peripheral small fiber dysfunction. In our study, CSP duration of the mastalgia side of the breasts was significantly longer. However, there was no significant difference for other EMG parameters.
The limitations of our study include the small number of patients and the fact that we did not examine the psychological status of the patients. In fact, some of the patients who met our study criteria did not accept psychiatric examination.
Conclusion
Albeit different reasons for mastalgia have been reported in the literature, a definite reason for mastalgia could not clearly be shown in these studies. CSP is thought to be prolonged due to dysfunction of the central nervous system mechanisms of pain modulation and because CSP has a role in pain. CSP in the EMG activity were monitored in our study with the aim of demonstrating that mastalgia may be due to central sensitization, which plays an important role in the formation of neuropathic pain, and our prolonged CSP results suggest a possible explanation for the etiology of this condition. In this respect, we believe that a larger contribution to understanding the etiology and developing treatments can be achieved with a wider series of cases.
Authorship Contributions
Concept: C.K., U.O.İ., E.B., M.M., Design: C.K., U.O.İ., E.B., M.M., Data Collection or Processing: C.K., E.B., N.P., M.T., Analysis or Interpretation: C.K., U.O.İ., E.B., M.T., M.M., Literature Search: C.K., U.O.İ., N.P., M.T., Writing: C.K., U.O.İ., E.B., M.T., M.M.
Conflict of Interest: No conflict of interest was declared by the authors.
Financial Disclosure: The authors declared that this study received no financial support.