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Duchenne Muscular Dystrophy

Duchenne muscular dystrophy
Objectives
  1. Describe the basic genetic and protein defect of Duchenne muscular dystrophy
  2. Describe the natural history of Duchenne muscular dystrophy
  3. Describe symptoms of muscular dystrophy in the 3 to 6 year age range
  4. Describe the philosophy of contracture control in the ambulatory patient
  5. Define indications for correction, and/ or prevention of spinal deformity for the patient with Duchenne muscular dystrophy

Discussion points
  1. What are active present areas of research in the field of muscular dystrophy?
  2. What is the Gower sign?

Discussion
Duchenne muscular dystrophy (sometimes called Meryon's disease, especially in British writings) is a relatively common form of muscular dystrophy, affecting about 1: 3500 live male births. It is transmitted in a sex-linked recessive pattern. Rare forms have been noted in females, and female carriers have a high percentage of subtle weakness and enzyme abnormalities. Boys generally develop normally until about age 3-6 when they may present with toe-walking, clumsiness, flatfootedness, tripping, or difficulty running or climbing stairs. The first muscle group displaying weakness is the gluteus maximus, with more weakness in the proximal muscles (quadriceps, hip abductors) than distal. Abdominal weakness also has an early onset. The anterior tibial is most affected below the knee. Pseudohypertrophy of the calf is common. Shoulder girdle weakness follows a few years later. Gait deteriorates, initially with increased lordosis to compensate for gluteus maximus weakness, then a waddling, wide based gait to compensate for hip abductor weakness and anterior tibial weakness. The Bower sign is an example of the effects of hip extensor and quadriceps weakness, manifested by the boy's use of hands and arms to push the knees into extension, compensating for the weakness. Contractures of the iliotibial band and heelcord are most common; inversion deformities of the foot and ankle are also common due to the persistence of activity in the posterior tibial tendon longer than other ankle motors.

Diagnosis is usually suspected by elevation of the serum creatine kinase level in the early stages of the disease. Creatine kinase appears to be associated with cell membrane permeability of muscle cells. The particular gene involved in Duchenne and Becker dystrophies was identified in 1982, and in 1987, its protein product, dystrophin, was identified. Histochemical studies of muscle can quantitate the amount of dystrophin present beneath the cell membrane; in Duchenne dystrophy there is none, in Becker dystrophy it is reduced. It is also reduced in many female carriers. Muscle biopsy is still the most used method of establishing the diagnosis, although molecular genetic techniques may be more used in the future. Dystrophin is essential for the stability of the muscle cell membrane, and its absence leads to disruption of the membrane and secondary degeneration, possibly through influx of calcium. Dystrophin is normally located on the internal surface of the cell membrane, and is also linked to F-actin.

Duchenne muscular dystrophy is associated with relentless progression of muscular weakness, with death usually resulting early in the third decade from cardiopulmonary problems. Walking usually becomes difficult, then impossible, at about age 10 with considerable variation. A program of regular stretching, heelcord lengthenings, soft tissue release, and transfer of the posterior tibial tendon, and brace support was documented to preserve ambulation on an average into the fourteenth year of life. Spinal deformity is common in teenaged boys with Duchenne dystrophy. Surgical stabilization of scoliosis is usually recommended when the curve exceeds 20 degrees, based on the logic that the curve will inevitably worsen, and pulmonary function will inevitably decrease. Surgical stabilization does not improve pulmonary function, but follow-up studies still reveal a high degree of patient satisfaction, despite a high complication rate. There is extensive recent literature on the technical details of spine stabilization for muscular dystrophy.

Other problems often associated with Duchenne muscular dystrophy are decreased cognitive dysfunction, small stature, osteopenia with increased fracture risk, and cardiac dysfunction. There is a great deal of research effort underway at present to develop better therapy for boys with muscular dystrophy, as our present treatment is largely supportive only. Much research is at the molecular biology level, and it is interesting to compare the titles of recent writings with those 10-20 years ago before the explosion of efforts at the molecular level. Prednisone is also currently being investigated as an adjunct to slowing the progressive weakness accompanying this disease. To continue to keep abreast in this field, some knowledge of molecular biology will be a necessity.

References
  1. Alman BA, Kim HK. Pelvic obliquity after fusion of the spine in Duchenne muscular dystrophy. Journal of Bone & Joint Surgery -British Volume 1999; 81( 5): 821-4.
  2. Billard C, Gillet P, Barthez M, Hommet C, Bertrand P. Reading ability and processing in Duchenne muscular dystrophy and spinal muscular atrophy. Developmental Medicine & Child Neurology 1998; 40( 1): 12-20.
  3. Bridwell KH, Baldus C, Iffrig TM, Lenke LG, Blanke K. Process measures and patient/ parent evaluation of surgical management of spinal deformities in patients with progressive flaccid neuromuscular scoliosis (Duchenne's muscular dystrophy and spinal muscular atrophy). Spine 1999; 24( 13): 1300-9.
  4. Brook PD, Kennedy JD, Stern LM, Sutherland AD, Foster BK. Spinal fusion in Duchenne's muscular dystrophy. Journal of Pediatric Orthopedics 1996; 16( 3): 324-31.
  5. Carter GT, McDonald CM. Preserving function in Duchenne dystrophy with long-term pulse prednisone therapy. American Journal of Physical Medicine & Rehabilitation 2000; 79( 5): 455-8.
  6. Cornu C, Goubel F, Fardeau M. Stiffness of knee extensors in Duchenne muscular dystrophy. Muscle & Nerve 1998; 21( 12): 1772-4.
  7. Dubowitz V. The muscular dystrophies--clarity or chaos? [editorial; comment]. New England Journal of Medicine 1997; 336( 9): 650-1.
  8. Emery AE. The muscular dystrophies. Bmj 1998; 317( 7164): 991-5.
  9. Fox HJ, Thomas CH, Thompson AG. Spinal instrumentation for Duchenne's muscular dystrophy: experience of hypotensive anaesthesia to minimise blood loss [see comments]. Journal of Pediatric Orthopedics 1997; 17( 6): 750-3.
  10. Gozal D. Pulmonary manifestations of neuromuscular disease with special reference to Duchenne muscular dystrophy and spinal muscular atrophy. Pediatric Pulmonology 2000; 29( 2): 141-50.
  11. Heller KD, Forst R, Forst J, Hengstler K. Scoliosis in Duchenne muscular dystrophy: aspects of orthotic treatment. Prosthetics & Orthotics International 1997; 21( 3): 202-9.
  12. Kennedy JD, Staples AJ, Brook PD, Parsons DW, Sutherland AD, Martin AJ, et al. Effect of spinal surgery on lung function in Duchenne muscular dystrophy. Thorax 1995; 50( 11): 1173-8.
  13. Larson CM, Henderson RC. Bone mineral density and fractures in boys with Duchenne muscular dystrophy. Journal of Pediatric Orthopedics 2000; 20( 1): 71-4.
  14. Marchesi D, Arlet V, Stricker U, Aebi M. Modification of the original Luque technique in the treatment of Duchenne's neuromuscular scoliosis [see comments]. Journal of Pediatric Orthopedics 1997; 17( 6): 743-9.
  15. McDonald CM, Abresch RT, Carter GT, Fowler WM, Jr., Johnson ER, Kilmer DD, et al. Profiles of neuromuscular diseases. Duchenne muscular dystrophy. American Journal of Physical Medicine & Rehabilitation 1995; 74( 5 Suppl): S70-92.
  16. Nagel BH, Mortier W, Elmlinger M, Wollmann HA, Schmitt K, Ranke MB. Short stature in Duchenne muscular dystrophy: a study of 34 patients. Acta Paediatrica 1999; 88( 1): 62-5.
  17. Ozawa E, Hagiwara Y, Yoshida M. Creatine kinase, cell membrane and Duchenne muscular dystrophy. Molecular & Cellular Biochemistry 1999; 190( 1-2): 143-51.
  18. Ramirez N, Richards BS, Warren PD, Williams GR. Complications after posterior spinal fusion in Duchenne's muscular dystrophy. Journal of Pediatric Orthopedics 1997; 17( 1): 109-14.
  19. Tawil R. Outlook for therapy in the muscular dystrophies. Seminars in Neurology 1999; 19( 1): 81-6.
  20. Thompson GH. Neuromuscular disorders. In: Morrissy RT, Weinstein SL, editors. Pediatric Orthopaedics. Philadelphia: Lippincott-Raven Press; 1996. p. 537-77.
  21. Tsao CY, Mendell JR. The childhood muscular dystrophies: making order out of chaos. Seminars in Neurology 1999; 19( 1): 9-23.
  22. Vignos PJ, Wagner MB, Karlinchak B, Katirji B. Evaluation of a program for long-term treatment of Duchenne muscular dystrophy. Experience at the University Hospitals of Cleveland. Journal of Bone & Joint Surgery -American Volume 1996; 78( 12): 1844-52.

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