What are the symptoms of muscular dystrophy?

Muscular Dystrophy Symptoms

Muscular dystrophies present with progressive skeletal muscle weakness and wasting as the hallmark feature, with the specific pattern, age of onset, and systemic complications varying significantly by genetic subtype.

Core Skeletal Muscle Manifestations

Progressive Muscle Weakness Pattern

• Progressive muscle weakness and wasting affecting skeletal muscles is the defining characteristic across all muscular dystrophies, with muscle fibers becoming destroyed and replaced by fatty and fibrous tissue 1.
• In Duchenne muscular dystrophy (DMD), the most common and severe childhood form, skeletal muscles are first noticeably affected around age 4 years, with patients experiencing progressive weakness following a proximal-to-distal pattern 1.
• Gradual decline in motor function leads to loss of ambulation typically in the early teens for DMD patients 1.
• Limb girdle muscular dystrophies (LGMD) demonstrate progressive weakness primarily affecting pelvic and shoulder girdle musculature, with proximal muscle weakness greater than distal 2.

Early Functional Signs

• Difficulty with activities requiring elevation against gravity progressively worsens, including timed Gowers' maneuver (rising from floor), climbing stairs, and rising from chairs 1.
• Facial, neck, and distal limb muscle weakness develops in myotonic dystrophy type 1 (DM1) 1.

Musculoskeletal Deformities

• Calf pseudohypertrophy appears in certain subtypes, particularly DMD and some LGMD variants 2.
• Scapular winging, progressive contractures, and scoliosis are common clinical features in multiple subtypes 2.
• Muscle imbalance leads to joint contractures, particularly affecting hip, knee, ankle joints, iliotibial band, hamstrings, and gastrocnemius in lower extremities 1.

Respiratory Symptoms

Progressive Respiratory Muscle Weakness

• Intercostal and diaphragm muscle weakness becomes noticeable after loss of ambulation in DMD, typically in adolescence and adulthood, though onset timing varies significantly 1.
• Inspiratory muscle weakness initially causes nocturnal hypoventilation and contributes to sleep-disordered breathing 1.
• Expiratory muscle weakness causes poor cough and inability to effectively manage respiratory secretions 1.

Respiratory Complications

• Respiratory failure and pneumonia develop as consequences of untreated respiratory muscle weakness 1.
• Progressive respiratory insufficiency and increased risk of respiratory infections occur in LGMD patients 2.
• Respiratory complications represent a major cause of morbidity and unplanned hospital admission, remaining the second most frequent cause of death in DMD after cardiac failure 1.

Cardiac Manifestations

Duchenne Muscular Dystrophy

• Progressive dilated cardiomyopathy develops as DMD affects heart muscle 1.
• Cardiac involvement is present in approximately 80% of DM1 patients, with higher risk in younger patients aged 2-30 years 1.

Myotonic Dystrophy

• Progressive atrioventricular or intraventricular conduction defects and tachyarrhythmias (ventricular and supraventricular) are the most life-threatening cardiac complications in DM1 1.
• Dilated cardiomyopathy has been reported in DM1, though conduction abnormalities predominate 1.
• In DM2, cardiac problems appear less severe (10-20%), with conduction defects normally limited to first-degree atrioventricular and bundle-branch block 1.

Limb Girdle Muscular Dystrophy

• Dilated and hypertrophic cardiomyopathies, atrial and ventricular arrhythmias, and various degrees of heart block occur, particularly common in lamin A/C-related LGMD (LGMD1B) and sarcoglycan-deficient LGMD (LGMD2C-F) 2.

Friedreich Ataxia

• Left ventricular hypertrophy with fibrosis and scarring, arrhythmias, and progressive heart failure develop, with cardiac dysfunction being the most frequent cause of death 1.

Myotonia (Specific to Myotonic Dystrophy)

• Myotonia (delayed muscle relaxation after contraction) characterizes both DM1 and DM2, presenting as a core clinical manifestation 1.

Systemic and Multiorgan Symptoms

Myotonic Dystrophy Specific

• Cataracts develop as part of the degenerative process in DM1 1.
• Neurological/neuropsychiatric deficits and endocrine/metabolic abnormalities occur in DM1 1.

Friedreich Ataxia

• Symptoms reflect mitochondrial dysfunction with variable severity of phenotypic features, typically with onset between ages 5-15 years 1.

Clinical Pitfalls and Important Considerations

• Heterogeneity in symptom onset and progression is substantial even within the same genetic subtype—respiratory symptoms in DMD show significant variability despite general patterns 1.
• Cardiac and respiratory complications interact bidirectionally—cardiac involvement impacts respiratory function, and respiratory failure can trigger cardiac arrhythmias or exacerbate cardiac failure 1.
• Genetic anticipation occurs in DM1, with successive generations showing symptoms at earlier ages or with more severe manifestations, but this does not occur in DM2 1.
• The average age of DMD diagnosis is 5 years despite earlier symptom onset, highlighting the importance of recognizing early signs 1.