Physical Therapy Haven

Population Characteristics:1,2,3

• Prevalence is 1.7 per 10,000
• Age of onset depends on type of muscular dystrophy (MD):
  • Duchenne muscular dystrophy (DMD): average age of onset is 3-5 years and primarily affects males
  • Becker muscular dystrophy (BMD): slightly later onset than DMD, primarily affects males

Pathophysiology:^4,5,6

DMD: 

• Caused by a genetic disorder in which a defect within the X chromosome leads to a complete or significant absence in the production of the protein dystrophin within muscle tissue
  • Lack of dystrophin production results in subsequent muscle degradation and atrophy

BMD:

• Caused by a genetic disorder of the X chromosome in which dystrophin is produced in abnormal molecular weights

Signs and Symptoms:7

• DMD symptoms are more deleterious and severe than BMD symptoms
• Progressive muscle weakness (proximal weakness typically precedes distal weakness) 
• Cardiomyopathy 
• Respiratory difficulty

Diagnosis:^6,8,9

• Diagnosis of MD is typically done by measuring serum creatine kinase concentrations and dystrophin quality 
  • Serum creatine kinase (CK) is elevated in patients with MD as a result of muscle degradation
    • CK is elevated at birth, making CK analysis particularly useful with differential diagnosis early in the lifespan
  • Dystrophin quality:
    • Less than 5% of normal quality is indicative of DMD
    • 5-20% of normal quality represents mild DMD to severe BMD
    • 20 to 50% of normal quality is representative of mild BMD 

Prognosis:9,10,11

DMD:

• Loss of ambulation between age of 6-15 years with mean age of 9.4 years
• Electric wheelchair dependent between 11-28 years with mean age of 14.6 years
• Assistance for eating and drinking between 12-23 years with mean age of 18.2 years
• Initiation of assisted ventilation between 14-31 years with mean age of 19.8 years
• Average life span of 35 years, cause of death is typically related to pneumonia accompanied with cardiac dysfunction

BMD:

• BMD prognosis is typically better than the prognosis of DMD due to the milder symptoms present in BMD 
• Patients typically are ambulatory at the age of 16 or even older 
• Average life expectancy extends into the mid 40's 

Physical Therapy Interventions:12

• Education on proper posture and positioning in order to prevent contractures and pressure sores
• Manual stretching
  • Active/active-assisted/passive stretching to prevent contractures at the ankle, hip, knee, shoulder, wrist, elbow, and fingers; becomes particularly important during non-ambulatory phase of disease
• Submaximal functional strengthening exercises:
  • Emphasized in the earlier stages of MD due to the elevated strength levels present during this stage of the disease
  • Helps prevent and slow the affects of progressive muscular atrophy and reduces risk of developing contractures
  • High-resistance strength training and eccentric exercises are not recommended, as these higher-demand activies can cause excessive overload and subsequent muscle fiber injuries
  • Aquatic therapy is useful in both the ambulatory and non-ambulatory phases due to the assistive nature of aquatic exercises
• Cardiopulmonary:
  • Education on lung-volume recruitment techniques
  • Manual assisted coughing and airway clearance techniques  

1. Parsons EP, Clarke AJ, Hood K, et al. Newborn screening for Duchenne muscular dystrophy: a psychosocial study. Arch Dis Child Fetal Neonatal Ed. 2002;86(1): F91-95.

2. NINDS muscular dystrophy information page. National Institute of Neurological Disorders and Stroke Web site. Available at http://www.ninds.nih.gov/disorders/md/md.htm. Accessed March 29, 2014. 

3. Bradley WG, Jones MZ, Mussini JM, et al. Becker-type muscular dytrophy. Muscle Nerve. 1978;1(2): 111-132.

4. Ervasti JM, Ohlendieck K, Kahl SD, et al. Deficiency of a glycoprotein component of the dystrophin complex in dystrophic muscle. Nature. 1990;345(6273): 315-319.

5. Hoffman EP, Fischbeck KH, Brown RH, et al. Characterization of dystrophin in muscle-biopsy specimens from patients with Duchenne's or Becker's muscular dystrophy. N Engl J Med. 1998;318(21) 1363-1368. 

6. Hoffman EP, Kunkel LM, Angelini C, et al. Improved diagnosis of Becker muscular dystrophy by dystrophin testing. Neurology. 1989;39(8): 1011-1017. 

7. Signs and symptoms. Muscular Dystrophy Association Web site. 2014. Available at: http://mda.org/disease/duchenne-muscular-dystrophy/signs-and-symptoms. Accessed March 29, 2014. 

8. Goldsein JA and McNally EM. Mechanisms of muscle weakness in muscular dystrophy. Journal of General Physiology. 2010;136(1): 29. 

9. Emery AE. The muscular dystrophies. Lancet. 2022;359(9307): 687-695.

10. Kohler M, Clarenbach CF, Bahler C, et al. Diasbility and survival in Duchenne muscular dystrophy. J Neurol Neurosurg Psychiatry. 2009;80(3): 320-325. 

11. Bushby KM, Garnder-Medwin D. the clinical, genetic and dystrophin characteristics of Becker muscular dystrophy. I. Natural history. J Neurol. 1993;240(2): 98-104. 

12. Bushby K, Finkel R, Bimkrant DJ., et al. Diagnosis and management of Duchenne muscular dystrophy, part 2: implemementation of multidisciplinary care. Lancet Neurol. 2010;9(2): 177-189.