Becker muscular dystrophy

Disease Description (Causes and Symptoms)

• Definition summary: An X-linked muscular disease caused by a defect in the dystrophin gene, resulting in progressive muscle weakness. It is a form with a later age of onset and slower progression than Duchenne muscular dystrophy (Becker type).
• Causes and pathophysiology: Abnormalities in the dystrophin gene on Xp21 (mostly gene deletions >90%; the remainder include point mutations). When the reading frame is preserved, an abnormal dystrophin protein with partial function is produced, resulting in milder symptoms or slower progression. Dystrophin deficiency causes instability of the muscle fiber membrane → repeated muscle fiber destruction and regeneration → fibrosis and fatty degeneration.
• Main symptoms: Usually begins with weakness in the lower limbs, particularly the proximal muscles, and progresses to the upper limbs; pseudohypertrophy of the calves, muscle atrophy, and reduced motor function (difficulty walking and climbing stairs). The age of onset is generally 5–25 years, and because progression is slow, walking impairment often does not occur until several decades later. Elevated serum CK (creatine kinase) levels. Cardiomyopathy and respiratory failure may occur (less frequently than in Duchenne muscular dystrophy).

Treatment Methods and Precautions

• Treatment goals: Relieve symptoms, prevent complications, and maintain daily functioning. There is no cure (symptomatic and multidisciplinary management).
• Drug treatment
  • Corticosteroids: There is evidence for maintaining muscle function in Duchenne muscular dystrophy, but the effect is inconsistent in Becker muscular dystrophy, so individualized decision-making is necessary. Whether to use them should be decided after assessing the risks and benefits with the treating specialist.
  • Cardiac treatment: When cardiomyopathy develops, standard heart failure treatment such as ACE inhibitors (or ARBs) and beta-blockers is used. Early cardiac treatment is important for prognosis.
• Rehabilitation and physical therapy: Regular physical therapy to maintain muscle strength and prevent joint contractures (aerobic and low-intensity strengthening exercises are recommended), with stretching to maintain joint range of motion. Avoid strenuous eccentric exercise and excessive muscle fatigue.
• Orthopedic intervention: Surgery may be considered when joint contractures or severe scoliosis require treatment, including surgical correction.
• Respiratory management: Regular monitoring of pulmonary function (vital capacity indicators such as FVC, etc.); polysomnography and noninvasive ventilation (NIV) may be considered if symptoms of sleep apnea or nocturnal hypoventilation occur.
• Vaccination and general care: Prevent respiratory infections (including influenza and pneumococcal vaccines), and manage nutrition and weight.
• Anesthesia and medication precautions: Depolarizing muscle relaxants and succinylcholine may pose risks such as hyperkalemia, so consultation with a specialist before anesthesia is necessary. Caution is also required with some myotoxic drugs (e.g., concomitant use of high-potency statins).
• Genetic counseling: Because this is an X-linked recessive condition, family and carrier testing and preconception counseling are recommended.
• Experimental treatment: Standard gene therapy for Becker muscular dystrophy is limited; participation in clinical trials (localized or targeted treatments) may be considered.

Checklist Before an Outpatient Visit (Including Examples of Items and Records to Prepare)

• Items and documents to prepare
  • List of medications and supplements currently being taken (including dosage and administration times)
  • Previous test results (genetic testing report, CK levels, electrocardiogram (ECG), echocardiogram (ECG/Echo), pulmonary function tests, etc.)
  • History of previous surgery and anesthesia, and family history (whether male or female family members have muscle weakness and the results of genetic testing)
• Symptom records (useful during the consultation)
  • When the initial symptoms began and how they progressed (changes in walking, going up and down stairs, frequency of falls)
  • Functional changes over the past 3–6 months (walking distance, use of assistive devices, breathing or sleep problems, level of fatigue, etc.)
  • Presence of pain, stiffness, or joint restrictions
• Information to tell the doctor before testing: Pregnancy plans, breastfeeding, comorbidities, and any recent infections
• Tests that may be requested during an outpatient visit: Serum CK, genetic testing orders and interpretation, electromyography (EMG), muscle biopsy (if necessary), ECG/echocardiogram, pulmonary function tests, and polysomnography (if symptomatic)

Examples of General Questions to Ask the Doctor

• "What are the expected benefits and side effects of this medication (or treatment)?"
• "How often should cardiac and respiratory function be tested?"
• "What should I be careful about in terms of lifestyle (exercise, nutrition, and daily activities)?"
• "How is the disease expected to progress, and what is the expected prognosis?"

Examples of Disease-Specific Questions

• "Based on the genetic testing results (the type of deletion or mutation), what is the risk of the disease occurring in my children, and what testing is recommended for family members (female carriers), and when should it be done?"
• "Based on the current cardiac function findings (ECG/Echo), when should prevention or treatment of cardiomyopathy be started (e.g., when to start an ACE inhibitor and how often to monitor)?"

(Summary of reference information: Becker muscular dystrophy is caused by mutations in the dystrophin gene. The age of onset is mainly 5–25 years, and it occurs in approximately 3–6 per 100,000 male births; about one-third of cases are reported to result from de novo mutations without a family history. Progression is slower than in Duchenne muscular dystrophy, but cardiac and respiratory complications are important factors affecting prognosis.)