Myotonic Dystrophy And Its Effect On Muscle Function And Mobility

What is Myotonic Dystrophy?

Myotonic dystrophy (DM), recognised as the prevalent type of muscular dystrophy in adults, is a genetic condition marked by advancing muscle weakness, myotonia (a condition where muscles don’t relax as quickly as normal after use), and the engagement of multiple body systems. While it predominantly targets the skeletal muscles, it doesn’t spare the heart, eyes, and the endocrine system from its effects.¹

What do occurrence and population trends tell us about DM?

Myotonic dystrophy is somewhat uncommon, with the global occurrence rates varying between 0.5 and 18.1 for every 100,000 people. The incidence of Myotonic Dystrophy Type 1 (DM1) is estimated to be about 1 in 8,000 births. Myotonic dystrophy affects males and females equally and can present at any age, although the symptoms and severity may vary significantly between individuals.²

Importance of understanding its effects on muscle function and mobility

Understanding the effects of myotonic dystrophy on muscle function and mobility is crucial for several reasons:

Early Diagnosis and Management: Recognizing the signs and symptoms early can lead to timely diagnosis and better disease management. Early intervention can help manage symptoms, improve quality of life, and slow the progression of muscle degeneration.

Improved Patient Outcomes: Knowledge of the disease's impact on mobility and muscle function aids in developing targeted therapies and rehabilitation programs can enhance the patients' physical abilities and reduce disability.³

Research and Treatment Development: Understanding the genetic and molecular mechanisms underlying myotonic dystrophy facilitates the development of new treatments and potential cures. Advances in gene therapy and the molecular medicine are promising areas of research that could significantly alter the disease's trajectory.⁴

Multisystemic Impact: Since myotonic dystrophy affects multiple organ systems, a comprehensive understanding is necessary for holistic patient care. This includes managing cardiac, respiratory, and endocrine complications commonly associated with the disease.

Varieties of Myotonic Dystrophy

Myotonic Dystrophy Type 1 (DM1)

Signs and development

DM1 presents a broad spectrum of symptoms due to its multisystemic nature. Notable characteristics encompass myotonia (prolonged muscle relaxation), advancing muscle weakness and atrophy, cataracts, cardiac conduction anomalies, and endocrine disruptors like insulin resistance. The intensity of symptoms can fluctuate widely, with some patients encountering mild muscle weakness while others face severe, potentially fatal complications. DM1 typically exhibits a pattern known as anticipation, where the symptoms emerge earlier and more intensely in subsequent generations.⁵

Myotonic Dystrophy Type 2 (DM2)

Symptoms and progression

DM2 exhibits akin to DM1, albeit generally with less severe symptoms and a delayed onset. Typical symptoms encompass muscle discomfort, rigidity, and weakness, primarily impacting the proximal muscles nearer to the body's core, such as the shoulders, hips, and thighs. DM2 also shows multisystem effects, including cataracts, cardiac complications, and endocrine disorders. However, DM2 does not usually exhibit the congenital form observed in DM1, and the phenomenon of anticipation is not as marked.

Effects of Myotonic Dystrophy on muscle function

Muscle weakness

Areas commonly affected

Myotonic dystrophy significantly impacts muscle function, with muscle weakness being one of the hallmark symptoms. In Myotonic Dystrophy Type 1 (DM1), muscle weakness predominantly affects the distal muscles, including the hands and feet. Conversely, in Myotonic Dystrophy Type 2 (DM2), the proximal muscles such as those in the shoulders, hips, and thighs are more commonly involved.⁶

Impact on daily activities

The progressive muscle weakness in both DM1 and DM2 leads to significant functional impairments. The patients often struggle with tasks that require fine motor skills, such as buttoning shirts or turning keys, due to weakness in the hands. Proximal muscle weakness can result in difficulty with activities such as climbing stairs, rising from a seated position, or lifting objects, profoundly affecting mobility and independence.⁷

Myotonia

Definition

Myotonia, characterised by delayed muscle relaxation after contraction, is a defining feature of myotonic dystrophy. Patients often experience stiffness and difficulty relaxing their muscles after voluntary movements, which can be particularly noticeable in the hands and face.

Effect on muscle relaxation and stiffness

Myotonic dystrophy causes muscle stiffness, especially after rest. This rigidity can worsen muscle weakness and create difficulties in everyday activities. For example, patients may find it hard to release objects or change their facial expressions swiftly.       

Muscle Atrophy

Progressive nature

Muscle atrophy is an advancing condition where the muscles progressively waste away and lose mass. This degeneration is tied to genetic alterations that interfere with the usual function and renewal of muscle cells. As the muscle fibers break down, individuals face ever-increasing weakness and a decrease in muscle size.

Long-term implications

The continuing consequences of muscle atrophy are significant, potentially leading to serious disability and reliance on others for routine care. Persistent muscle degradation may necessitate the use of mobility support devices like wheelchairs, and interventions might be required to aid with respiration and other bodily functions if the muscles involved in breathing are impacted. Furthermore, muscle atrophy plays a role in the comprehensive physical deterioration and diminished life quality experienced by individuals with myotonic dystrophy.

Effects of Myotonic Dystrophy on mobility

Gait abnormalities

Common patterns and causes

Myotonic dystrophy significantly affects gait due to muscle weakness, myotonia, and central nervous system involvement. Common gait abnormalities include slower walking speeds, and shorter stride lengths. Patients often exhibit a higher pelvic tilt, reduced hip extension, knee hyperextension during midstance, and increased backward bending of the ankle during the stance phase.⁸

Impact on balance and coordination

The abnormalities in gait patterns lead to significant balance and coordination issues. Patients with DM1, for instance, show worsening in muscle force, balance, and increased risk of falls. Over a five-year period, significant declines in balance were observed, leading to a higher incidence of falls, particularly in men

Fatigue

Frequency and severity

Fatigue is a prevalent and debilitating symptom in myotonic dystrophy, affecting over 79% of patients. It is severe and persistent, significantly impacting the ability to perform daily activities and reducing overall quality of life.⁹

Relationship with mobility

Fatigue intensifies mobility challenges by restricting the endurance and physical activity levels of patients. It prompts a cycle of diminished activity and additional muscle weakness,  making it harder for patients to sustain independence in their everyday lives. The link between the severity of fatigue and mobility hindrance underscores the necessity for holistic management approaches to tackle both symptoms.

Adaptive strategies

Physical therapy and exercises

Physical therapy is pivotal in addressing mobility problems in myotonic dystrophy. Customised exercise regimes  on strength training, balance, and gait enhancement have demonstrated substantial advantages. For example, a 10-week personalised exercise program conducted at home led to improvements in functional mobility, balance, and strength in the lower limbs of DM1 patients.¹⁰

Assistive devices and technology

Thesupportive devices, like orthoses and hybrid assistive limbs (HAL), can boost mobility and life quality for individuals with myotonic dystrophy. Gait training using HAL has been proven to enhance walking distance, speed of gait, and overall life quality in patients experiencing progressive gait disturbances. These devices aid in offsetting muscle weakness and offer support during movement, thereby reducing fall risks and promoting independence.

Diagnosis and monitoring of Myotonic Dystrophy

Genetic testing

Early genetic testing allows to detect myotonic dystrophy even before symptoms appear. This is particularly important for families with a history of the disorder, as it enables early intervention to regain better condition. Genetic testing can also be used prenatally to determine if a foetus has inherited the disorder, thus aiding in family planning and early medical decision-making.

Role in Electromyography (EMG) in assessing muscle function

Electromyography (EMG) is a crucial method for assessing muscle function in myotonic dystrophy patients. By measuring muscle electrical activity during both rest and contraction, EMG provides valuable insights into muscle health. 

Management and treatment of Myotonic Dystrophy

• Pharmacological Interventions

Pharmacological treatments for myotonic dystrophy focus primarily on symptom relief, particularly for myotonia (delayed muscle relaxation). Mexiletine, a sodium channel blocker, has reduces myotonia symptoms, and improving patients' ability to perform daily activities.¹¹

• Lifestyle Modifications

Lifestyle adjustments are crucial for managing myotonic dystrophy symptoms and enhancing quality of life. Patients should embrace healthy practices like maintaining a balanced diet, getting sufficient rest, and practising stress management. These modifications can ease fatigue and promote overall well-being.

• Supportive Care

Effective management of myotonic dystrophy requires a multidisciplinary approach involving neurologists, cardiologists, physiotherapists, and other healthcare professionals. This collaborative effort ensures comprehensive care, addressing the various systemic complications associated with the disease, such as cardiac, respiratory, and endocrine issues.

• Importance of Patient Education and Support Groups

Educating patients and their families about myotonic dystrophy is crucial for effective disease management. Support groups and patient education programs provide valuable resources, emotional support, practical advice, and helping patients navigate the challenges of living with myotonic dystrophy.

Summary

Myotonic dystrophy, the most common form of muscular dystrophy in adults, is a complex condition that affects multiple systems in the body, including the heart, eyes, and the endocrine system. It is marked by progressive muscle weakness and a prolonged muscle contraction (myotonia). DM is a global condition, with DM Type 1 impacting approximately 1 in 8,000 newborns. The symptoms of DM are diverse and can significantly affect a person's mobility and daily life due to the muscle weakness and abnormalities in walking. Therefore, early detection is essential for symptom management and enhancing patient outcomes. Investigating the genetic and molecular underpinnings of DM is crucial for the targeted treatments. Current treatment strategies encompass pharmacological interventions such as Mexiletine, modifications in lifestyle, physical therapy, and the use of devices to improve mobility. An all-inclusive approach involving multiple disciplines and patient education is critical for providing comprehensive care and enhancing the quality of life for those living with myotonic dystrophy.