Herein, we measured skin stiffness on the upper arm and forearm of patients with unilateral BCRL using MyotonPRO and found that the lymphedema limb had considerable skin stiffness. To the best of our knowledge, this is the first report that demonstrates the utility of the MyotonPRO in assessing skin stiffness in BCRL.
Herein, we demonstrated that the MyotonPRO can measure BCRL skin stiffness using an L-shaped probe with an arm length of 20 mm, disc attachment (10 mm diameter), and a special adhesive seal on the disc at the tip. BCRL is considered problematic because it limits upper extremity movement and sensation, thereby increasing psychosocial, economic and time burdens, and impairing quality of life [4-6]. Therefore, studies have been conducted to evaluate skin stiffness using MyotonPRO to properly evaluate and treat BCRL. In a study in which measurements were made with a 12-mm disc device attached to a regular stick probe, the stiffness of the upper limb with lymphedema was lower than that of the healthy limb [22]. The skin of the limbs with lymphedema is stiffer than the normal skin, and the longer the time elapsed from disease onset, the more hardening occurs [23]. Thus, the results could have been some kind of measurement error. One of the reasons for this was the use of a regular stick probe for skin stiffness evaluation. Because the vibration of a regular stick probe moves in a vertical direction, it may have measured biomechanical properties of the deep bone [13]. Conversely, skin stiffness can be properly measured when an L-shaped probe is used for measurement because the vibration direction is horizontal.
Our patients had a median time since lymphedema onset of 836 days. Therefore, it is possible to quantify skin stiffness in chronic BCRL using the L-shaped probe with disc attachment on the MyotonPRO. This would help lymphedema therapists objectively assess what has been a subjective assessment of skin stiffness. This study is very important because the results show that skin stiffness in lymphedema can be evaluated objectively. In the future, measuring skin stiffness with MyotonPRO before the onset of subjective symptoms of lymphedema may allow for early detection of BCRL. As a result, CPT may be started at an early stage of lymphedema, thereby reducing exacerbations. In addition, objective evaluation of the effect of treatment may be possible by measuring the skin stiffness before and after CPT.
In addition to lymphedema, other causes of oedema include disuse. Among other causes, disuse oedema is caused by reduced muscle pump action, although older adults with exercise habits are said to maintain muscle pump action [24]. Since the study participants were outpatients with independent activities of daily living and only a few patients had sarcopenia, the incidence of disuse oedema was considered low in the population. The usefulness of MyotonPRO in the evaluation of disuse oedema is unknown and needs further study.
Obesity is a risk factor for BCRL development after breast cancer treatment [25]. Furthermore, obesity negatively affected the later development of secondary lymphedema [26]. Studies have also reported that obesity is positively correlated with the occurrence, recurrence, treatment failure and prolonged treatment of cellulitis [27-30]. In the present study, patients with a history of cellulitis had a significantly higher BMI than those without. Upper extremity cellulitis occurs less frequently than lower extremity cellulitis; however, when it does occur, the risk of recurrence is increased, and lymphedema is exacerbated [31, 32]. However, no association was demonstrated between the frequency of cellulitis onset and skin stiffness in this study. Patients in this study were on CPT, and CPT may have prevented BCRL worsening after cellulitis onset. Thus, appropriate CPT may be important to avoid exacerbating skin stiffness. Multiple regression analysis showed that diabetes affected skin stiffness in BCRL. The skin stiffness of the plantar feet in patients with diabetic neuropathy is harder than that of normal plantar feet [33]. Although whether this study patient had diabetic neuropathy is still unknown, diabetes may have negatively affected skin stiffness in the lymphedema limb. Further case accumulation will clarify the relationship between worsening skin stiffness in lymphedema and diabetes.
The number of axillary lymph nodes dissected, lymph node metastases and docetaxel use have been associated with BCRL development [34-36]. Because this study included patients with BCRL, to what extent the aforementioned factors contributed to BCRL development is unclear; however, in patients who underwent axillary lymph node dissection at initial surgery, the number of days to BCRL development was not associated with the number of lymph nodes dissected, lymph node metastases or docetaxel use. In addition, no association was found between skin stiffness and the number of axillary lymph nodes dissected or the number of lymph nodes with metastases. Therefore, these are considered risk factors for BCRL development based on previous reports; however, whether these factors affect skin stiffness after BCRL development is unclear.
Limitations
This study has several limitations. First, many patients in this study were on CPT for chronic BCRL. Therefore, whether MyotonPRO can detect skin stiffness before starting CPT or mild cases early in the disease course is unclear. However, because CPT is thought to improve skin stiffness, MyotonPRO may detect skin stiffness even before starting CPT. If skin stiffness can be detected early in the disease onset or before symptoms appear, CPT can be performed at an early stage, and BCRL deterioration can be prevented. Second, measurements were taken in the supine position with the shoulder joint in 90° of abduction and external rotation and the elbow joint in 90° of flexion. Although skin stiffness may change with changes in limb position, because the lymphedema limb was compared with a healthy limb at the same limb position and site, the result that the skin of the lymphedema limb being significantly stiffer was not considered problematic.