May 30, 2024
Duchenne Muscular Dystrophies muscle

Duchenne Muscular Dystrophy (DMD) is the commonest of all muscular dystrophies due to defects in the X chromosome.

Xp21 on X chromosome

1: 3500 male birth

X-Linked recessive transmission; So only in BOYS (or in girls with sex chromosome disorder)

Failure to code in the dystrophin gene

Dystrophin gene: Required for the stability of cell membrane of cardiac and skeletal muscles

Clinical Features of Duchenne Muscular Dystrophies

Symptoms began at the age of 3-6 years with insidious onset

Key role: Diagnosis of disease early birth of another affected child can be avoided

Proximal muscle is affected first than distal (Glutei, quadriceps, tibialis anterior)

Wide-based stance and gait

Foot: Equinus

Pelvic: Anterior tilt

Lordotic Spine

Extended neck

Calf muscle: Bulky ( Replacement of fat -> Psuedohypertrophy)

Difficult in standing and climbing: Can’t run properly=Frequent falls

Grower’s Sign: The child climbs up supporting his own leg due to Gluteus Maximus and thigh muscles

Upper limb weakness follows around 3-5 years

At 10 years child becomes dependent on a wheelchair, rapid deterioration of spinal posture (Scoliosis)

At < 30 years: Cardio-pulmonary failure is the Cause of Death

Laboratory:

Increase excretion of creatine

Decrease creatinine in urine

Creatine: Synthesize from glycine and other amino acids in the liver and is deposited in muscle

Creatinine: Arises from muscle creatine due to loss of phosphate from creatine phosphate

When the muscle is destroyed: It is less capable of storing creating= excreated rather than converting to creatinine

Normal :

  • Creatinine excretion: 22 mg/ kg/ 24 hr
  • Creatine excretion: 2-3 mg/kg/24 hr

Serum enzymes

Elevation of serum aldose and creatine phosphokinase (diagnostic of myopathy)

[ Creatine phosphate (Increase in skeletal muscles) is more specific than aldolase]= Also found in nonmuscular sites (Liver and blood cells)

24-hour urinary creatine excretion

For a quantitative assessment of the progression of the disease

Electromyographic Studies

Individual motor unit potential decreases in size during voluntary contraction and the number and rate of unit firing increase

Genetic testing

DNA polymerase chain reaction

Muscle Biopsy

Tissue obtained from the weakest accessible muscle

< 50% strength : More likely to give (+) biopsy

Vastus lateralis: Most common muscle biopsy

Dystrophin analysis can be done

Pathology

Gross Appearance:

  • Enlarged gastrocnemii: Fatty tumors (not like muscles)
  • Other muscles are small: Color varies from yellowish to pinkish-gray
  • Pale translucent appearances: Resembling fish flesh
  • Depends upon the relative amount of fat/ fibrous tissue
  • Which replaces muscle fibers

Microscopic Appearance:

  • Loss of muscle fibers due to segmental necrosis
  • Subsequent fragmentation of fibers
  • Necrosis:- Phagocytosis and proliferation of histocytes in these zones
  • Sacrolemma nuclei: Enlarged
  • Increase interstitial connective tissue
  • Infiltration of fatty/ adipose tissue
  • Heart: Myocardial fibrosis

Treatment Options:

Duchenne Muscular Dystrophies treatment is explained below

No definite treatment : Ultimate fatal

Principle :

Achieving stabilization and balance so as to enable the patient to ambulate independently or with little support for a long period

Medical Therapy:

Corticosteroids:

  • Their anti-inflammatory action can help in preserving muscle strength and increase the duration of ambulation
  • Side effects: Osteoporosis, Risk of fractures, Cataracts

Glutamine and creatine have mixed responses but are well tolerated

Aminoglycosides (Eg. Gentamycin):- Also shows improvement in muscle power — where defects are due to stop codon

Physical and Surgical Therapy

Maximize the duration of ambulation and prevent complications of immobilization:- Once the child loses the power to move independently

Instructions for exercises, stretching, and walking with crutches

Contracture of the lower extremity frequently develops at an early age; especially in the calf muscle, tensor fascia lata, iliotibial band, and equinus deformity of the foot associated with some flexion deformity of hip, Knee, lumbar lordosis

Contracture must be treated at an early stage by stretching and splinting at night

If contracture progresses: Surgical correction may be necessary

Heel cords

Released by subcutaneous tenotomies and toe to groin cast applied with knees in extension and the ankles in 10-degree dorsiflexion

Following this procedure: Patient no longer can stabilize knee provided by fixed plantar flexion of feet

Consequently, the long brace may be worn

Tight iliotibial bands

Released by Yount’s Procedure

The large rectangular segment of the band to the corresponding intermuscular septum removed

The hip and knee show maximum flexion contracture

Posterior tibial Muscle

Always retain considerable power for long periods

Can be transferred by interosseous route to 3rd cuneiform to reinforce dorsiflexion

Postoperatively: Patients are immediately allowed to walk, if necessary with a walking cast

Followed by bracing

Because immobilizing these patients rapidly weakens them

Management of Scoliosis

Curve progression occurs: Can be up to 90 degrees

Previously: To retards the progression of scoliosis plastic jacket/corset was used but is avoided nowadays

No role in the prevention of curve progression but further decreases the pulmonary function

If scoliosis is marked ( > 30 degrees): Instrumentation and spinal fusion are advised which maintain pulmonary function and improve quality of life

But if the life span is < 2 years: Spinal surgery is contraindicated

Gene therapy: Dystrophin in the form of myoblast is introduced: Have not been successful in humans

Details on Scoliosis