Becker Muscular Dystrophy

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Original Editor - Shreya Pavaskar
Top Contributors - Shreya Pavaskar, Rucha Gadgil, Uchechukwu Chukwuemeka, Laura Ritchie, Kim Jackson and Kirenga Bamurange Liliane

Introduction

Becker muscular dystrophy (BMD)—one of a spectrum of X-linked muscular dystrophies shows the same pattern of muscle involvement as seen in Duchenne muscular dystrophy (DMD), but with a more slowly progressive clinical course.

Clinically Relevant Anatomy

Dystrophin is responsible for connecting the cytoskeleton of each muscle fiber to the underlying basal lamina. The absence of dystrophin stops calcium entering the cell membrane affecting the signaling of the cell, water enters the mitochondria causing the cell the burst. In a complex cascading process that involves several pathways, increased oxidative stress within the cell damages the sarcolemma resulting in the death of the cell, and muscle fibers undergo necrosis and are replaced with connective tissue.

Pathological Process

BMD is a type of recessive, X-linked dystrophinopathy. Clinical variations in patients with BMD are due to differences in dystrophin mutations from exon deletions.

Dystrophin levels in BMD are generally 30-80% of normal, while in DMD, the levels are less than 5%.

Clinical Presentation

• Delayed developmental motor milestones might be the first observation from parents.
• Clumsy
• Frequent falls
• Difficulty rising from floor, may show Gowers's sign (non-specific)
• Subclinical cases may manifest later in life; dilated cardiomyopathy can be the first sign of BMD.
• Contractures
• Weakness may be limited to specific proximal muscles
• Preservation of neck flexor muscle strength may be present
  

Diagnostic Procedures

• Serum creatine kinase - moderate to severe elevation
• Dystrophin gene deletion analysis by gene analysis
• Muscle biopsy with dystrophin antibody staining
• Cardiac magnetic resonance imaging (MRI) 
• Electromyography
• Nerve conduction studies - expected to be normal
• Electrocardiogram/Echocardiogram 
• Pulmonary function test
• X-rays to detect any bone abnormalities due to contractures and wasting of muscles

Outcome Measures

Outcome measures to quantify disease progression, including:

• 6‐minute walking test
• North Star ambulatory assessment scale,
• Time taken to climb four steps
• Time taken to rise from the floor
• Performance of upper limb.

One of the limitations of these measures is the fact they target either ambulant or non‐ambulant patients. However, as the disease progresses, the outcome measures change making it difficult to use a single outcome measure to analyze the patient. Studies are being carried out to create a uniform measure for the muscular dystrophies.

Medical Management

No medications are provided to patients for the specific treatment of BMD.

Medications are administered to treat symptoms that are commonly are associated with BMD (such as cardiac medications for heart disease).

Corticosteroid medications to help individuals remain able to walk for as long as possible by delaying the inflammatory process.

Differential Diagnosis

• Duchenne muscular dystrophy
• Distal muscular dystrophy
• Scapulo-humeral dystrophy
• Spinal muscular atrophy
• Inflammatory myopathy

Resources

Muscular Dystrophy

Duchenne Muscular Dystrophy - A Case Study