Duchenne Muscular Dystrophy and the Viscoelastic Properties of Upper Limb Muscles

Overview

Muscular dystrophies are hereditary and progressive skeletal muscle diseases that cause degeneration and loss of strength in the muscles. The most common form is Duchenne Muscular Dystrophy (DMD), which is X-linked recessive and develops due to a mutation in the dystrophin gene. Dystrophin is a membrane protein found in skeletal muscle, cardiac muscle, vascular smooth muscle, and the brain, functioning as a component of the glycoprotein complex. In the absence of dystrophin, proteases break down the glycoprotein complex, resulting in the loss of membrane proteins, which leads to degeneration and weakness of muscle fibres. In addition to skeletal muscle, involvement of the respiratory and cardiac muscles is the most important cause of morbidity and mortality. Children with DMD are usually diagnosed with abnormal gait, frequent falls, and difficulty climbing stairs. Progressive functional loss is observed over time. Although the disease usually begins in the lower extremities, it eventually affects the upper extremities as well. Early stage: Lower extremity muscles are more affected (walking and climbing stairs become difficult). Advanced stages: Shoulder girdle, arm, and hand muscles begin to be affected. Weakness is particularly seen in the deltoid, biceps, and triceps muscles. There is limited shoulder movement and difficulty raising the arm. Therefore, functional losses are seen in the upper extremities. Functional losses generally cause difficulties in daily living activities; tasks requiring upper limb use, such as dressing, eating, and combing hair, become difficult. Hand skills (fine motor functions) are usually affected later, but distal muscles may also weaken over time. In summary, upper limb muscles weaken in individuals with DMD as the disease progresses. This can affect the individual's daily living activities. Regular monitoring of upper limb function, appropriate rehabilitation programmes, and supportive treatments aimed at improving quality of life are of great importance.

Due to the rapid progression of muscle weakness and accompanying contractures, children often become dependent on wheelchairs by the age of 12. Loss of ambulation, muscle weakness and atrophy progress rapidly, leading to limited movement and contractures in the lower limbs. The same processes are observed in the upper limb muscles following the lower limbs. With the decline in upper limb function towards the middle of the first decade, children lose their feeding and self-care skills. The progression of weakness continues into the second decade. The function of the distal muscles is often preserved enough to allow the use of eating utensils, a pen, or a computer keyboard. Regular monitoring of upper limb function, appropriate rehabilitation programmes, and supportive treatments aimed at improving quality of life are of great importance. The most important things that can be done for this disease are the treatment of complications and improving the quality of life of affected children. Muscle and connective tissue are referred to as 'viscoelastic' tissues because they possess both viscosity and elasticity properties. Very rigid structures are more viscous and less elastic, while soft structures are more elastic and less viscous. Myotonometry allows us to objectively and quantitatively examine parameters such as the passive stiffness, elasticity, and tone of upper limb muscles, thereby making a significant contribution to current clinical assessments. This enables us to go beyond subjective evaluations and allows for more sensitive monitoring of progressive changes. Myotonometry has generally been used in healthy individuals or in neurological/rheumatological diseases. However, its use in DMD, particularly for upper limb muscles, is limited in the literature. Therefore, your study could be a pioneering work demonstrating the specific applications of the myotonometry device in DMD. This study will be conducted at the Gaziantep Metropolitan Municipality Disability-Free Living Centre. The study is planned as an observational, cross-sectional descriptive study to examine the myotonometric characteristics of the upper limb muscles in individuals diagnosed with Duchenne Muscular Dystrophy (DMD). It is a cross-sectional descriptive study. Thirty male individuals aged 5-18 years with a genetically or biopsy-confirmed diagnosis of DMD will be included in the study. These individuals will be categorised into three groups: 5-8, 9-12, and 13-17 years of age and compared with a healthy peer group. Healthy peers will include children and relatives of academic and administrative staff of the SANKO University Faculty of Health Sciences. As individuals in both groups are under 18 years of age, voluntary consent forms will also be obtained from their families. Only the dominant extremity of each individual included in the study will be measured. For those participating in the study, demographic information forms and voluntary consent forms will first be completed by their families. Subsequently, for our assessments, the Myoton PRO device will be used to measure the passive mechanical properties (muscle tone, stiffness, elasticity) of our target muscles. To assess upper limb functionality: Nine-Hole PEG Test and 6-Minute Pegboard Test. To assess muscle strength: Muscle Tester (Manual Muscle Testing Device). To assess quality of life: SF-12 Quality of Life Scale. Assessments will take approximately 30 minutes. Rest periods will be included to prevent fatigue. Families will be present in the assessment environment during the assessments.