Neurology

Duchenne Muscular Dystrophy

Background

  • Most common genetic disorder (1:3000 births worldwide)
    • X-linked recessive
  • Target both cardiac and skeletal muscle
  • Born with seemingly normal anatomy and strength but begin to exhibit symptoms by age 3
  • Patient are wheelchair bound by their early teens
  • Death usually occurs in the 4th decade of life
  • Caused by deleterious mutations in the protein dystrophin (encoded by gene DMD)

Clinical Symptoms

  • Difficulty rising from floor
  • Bilateral gastrocnemius hypertrophy
  • Generalized muscle pain and weakness
  • Altered or slowed gait

Clinical Management

  • Provide symptomatic support
  • Early treatment: Oral corticosteroids
    • Lengthen the age at which ambulation is lost by about two years
  • Orthopedic bracing of joints and limbs to prevent stricture and scoliosis
  • Watch for decline in the muscles of respiration (major contributor to morbidity and mortality)
    • First signs of respiratory decline observed during sleep (monitor for nocturnal hypoxia)
      • Once noctural hypoxia is present, provide ventilatory support at night
      • Decreased respiratory muscle function leads to increased pulmonary infections as well (unable to cough productively and clear the airway)
    • Perform pulmonary function tests
  • Track cardiac function with echocardiography and MRI
    • Cardiomyopathy begins in the teenage years
    • Reduce afterload and contractile strength (beta-blockers, fluid and electrolyte balance)

​References

Birnkrant, D. J., et al. (2010). "The respiratory management of patients with duchenne muscular dystrophy: a DMD care considerations working group specialty article." Pediatr Pulmonol 45(8): 739-748.

De Luca, A. (2012). "Pre-clinical drug tests in the mdx mouse as a model of dystrophinopathies: an overview." Acta Myol 31(1): 40-47. 

Flanigan, K. M., et al. (2013). "LTBP4 genotype predicts age of ambulatory loss in Duchenne muscular dystrophy." Ann Neurol 73(4): 481-488.

Gardner, B. B., et al. (2015). "Cardiac function in muscular dystrophy associates with abdominal muscle pathology." J Neuromuscul Dis 2(1): 39-49.

Hack, A. A., et al. (1998). "γ-Sarcoglycan deficiency leads to muscle membrane defects and apoptosis independent of dystrophin." The Journal of cell biology 142(5): 1279-1287.

Heydemann, A. and E. McNally (2009). "NO more muscle fatigue." J Clin Invest 119(3): 448-450. 

Nelson, S. F. and R. C. Griggs (2011). "Predicting the severity of Duchenne muscular dystrophy Implications for treatment." Neurology 76(3): 208-209. 

Pearson, C. M. (1962). "Histopathological features of muscle in the preclinical stages of muscular dystrophy." Brain 85: 109-120.