Muscular Dystrophies

By admin On Feb 12, 2024

Ovid: 5-Minute Orthopaedic Consult

Editors: Frassica, Frank J.; Sponseller, Paul D.; Wilckens, John H.

Title: 5-Minute Orthopaedic Consult, 2nd Edition

> Table of Contents > Muscular Dystrophies

Muscular Dystrophies

Paul D. Sponseller MD

Basics

Description

Muscular dystrophies are a group of
inherited disorders characterized by progressive degeneration and
weakness of skeletal muscle without apparent cause in the nervous
system.
Skeletal and cardiac muscles are affected, and secondary effects occur in the lungs, skeleton, and many other systems.
These conditions have been categorized by
clinical distribution, severity of muscle weakness, and pattern of
genetic inheritance.
Because of limited space, only Duchenne muscular dystrophy is described in detail (Fig. 1).
Classification:
- Sex-linked muscular dystrophy: Duchenne muscular dystrophy, Becker, Emery-Dreifuss
- Autosomal-recessive muscular dystrophy: Limb-girdle, infantile fascioscapulohumeral
- Autosomal-dominant muscular dystrophy: Fascioscapulohumeral, distal, ocular, oculopharyngeal

Epidemiology

Incidence

Duchenne muscular dystrophy occurs in young boys.
Duchenne muscular dystrophy occurs in 1 in 3,500 live male births (1).
Becker dystrophy occurs in ~1 in 30,000 live male births (1).

Fig. 1. This series of 6 drawings illustrates the Gower maneuver of a 7-year-old child with Duchenne muscular dystrophy.

Risk Factors

Male gender

Genetics

Duchenne muscular dystrophy is sex-linked, as is Becker-type tardive dystrophy.
Other dystrophies are autosomal recessive and autosomal dominant.

Etiology

A single gene defect in the short arm of
the X chromosome has been identified as being responsible for Duchenne
muscular dystrophy and Becker muscular dystrophy.
- The gene encodes the protein dystrophin, which is a component of the cell membrane cytoskeleton.

Diagnosis

Signs and Symptoms

Duchenne muscular dystrophy:
- The disease occurs only in males, and it usually becomes evident at 3–6 years of age.
- Common presentations include:
  - Delayed walking
  - “Waddling,” Trendelenburg gait, or lordotic gait
  - Frequent tripping and falling
  - Inability to hop and jump
- Progressive weakness occurs in the
  proximal muscle groups, including the gluteus, quadriceps, abdominal
  muscles, and shoulder girdle muscles
- Pseudohypertrophy and contracture of calf muscles is common.
- Most patients have cardiac involvement, most commonly tachycardia and right ventricular hypertrophy.
- Many also have static encephalopathy with mental retardation.
- Death from pulmonary and cardiac failure occurs during the 2nd or 3rd decade of life.
- Because of hip muscle weakness, patients
  compensate by carrying the head and shoulders behind the pelvis during
  gait, thus producing an anterior pelvic tilt and increased lumbar
  lordosis.
- Weakness in the shoulder girdle occurs 3–5 years after presentation.
  - It is difficult to lift the patient under the arms because of the weakness.
  - This weakness has been termed the “Meryon” sign.
- No sensory deficits are detected.
- Children usually are unable to ambulate effectively beyond 10 years of age.
Becker muscular dystrophy:
- Similar to Duchenne muscular dystrophy in clinical appearance and distribution of weakness, but less severe
- The onset usually occurs after the age of 7 years.
- The rate of progression is slower than in Duchenne muscular dystrophy
Many more types of muscular dystrophy exist (not described here).

P.267

Physical Exam

History, physical examination,
measurement of creatine phosphokinase and dystrophin, and
electromyography help in making the diagnosis.
Electromyography shows a myopathic pattern, with reduced amplitude, short duration, and polyphasic muscle action potentials.
Muscle biopsy also may be performed.
Evaluate muscle bulk to assess for pseudohypertrophy of the calves.
Observe the patient’s gait and look for Trendelenburg gait.
Starting proximally, look for muscle weakness.
Evaluate the patient’s ability to stabilize the shoulder; test for Meryon sign.
Note contracture, developing later, followed by scoliosis.

Tests

Lab

Serum creatine phosphokinase markedly is elevated in the early stages of Duchenne muscular dystrophy.
- It may be 200 times normal, but it later declines as muscle degeneration becomes complete.
Dystrophin levels are completely absent in Duchenne muscular dystrophy; they are less than normal in Becker dystrophy.

Pathological Findings

Muscle degeneration, with subsequent loss of fibers
Variation in fiber size
Proliferation of connective tissue

Differential Diagnosis

Peripheral neuropathy
Anterior horn cell disease
Poliomyelitis

Treatment

General Measures

Most patients with Duchenne muscular dystrophy die in
their 2nd or 3rd decade of life; therefore, orthopaedic treatment
should be designed to improve or maintain the functional capacity of
the involved adolescent.

Activity

No restrictions on activity.
Activity is to be encouraged as much as possible.

Special Therapy

Physical Therapy

Test muscle strength to assess the rate of deterioration.
Use ankle-foot orthoses for correctable deformities.
The best treatment for fractures is closed reduction and immobilization.
Fractures of the lower extremities occur
frequently in children with Duchenne muscular dystrophy, especially in
children who are wheelchair bound.
Contractures of both lower and upper extremities may occur.
- Surgical release of contractures sometimes is indicated to improve function.
~95% of patients with Duchenne muscular dystrophy develop progressive scoliosis (2).
- Surgical correction of scoliosis improves sitting balance and minimizes pelvic obliquity.
- Posterior spinal fusion is recommended for curves of >20–30°.
Programs of vigorous respiratory therapy
and the use of home negative-pressure and positive-pressure ventilators
may promote life extension.
Proper diagnosis and early genetic
counseling may help parents to be aware of the risk of additional male
infants with Duchenne muscular dystrophy.

Medication

No drugs have been proved effective.
Steroids have some benefit (delaying
scoliosis and prolonging function), but they also are associated with
long-term problems, including weight gain and osteoporosis.

Surgery

Contracture release (Achilles, fascia lata) may be indicated.
Correction of scoliosis involves fusion of nearly the entire thoracic and lumbar spine (T2–L5 or sacrum).
- Rods are used to straighten and hold the spine.
- This intervention should be performed for curves of ≥30°.

Follow-up

Prognosis

Duchenne muscular dystrophy is fatal in the 2nd or 3rd decade of life.
Becker dystrophy is more slowly progressive, and life expectancy is greater.

Complications

Respiratory failure
Cardiac failure
Fracture
Scoliosis

Patient Monitoring

Patients must be followed frequently (every 4–6 months) by a neurologist to assess their progression.

References

1. Alman BA, Raza SN, Biggar WD. Steroid treatment and the development of scoliosis in males with Duchenne muscular dystrophy. J Bone Joint Surg 2004;86A:519–524.

2. Biggar WD, Gingras M, Fehlings DL, et al. Deflazacort treatment of Duchenne muscular dystrophy. J Pediatr 2001;138:45–50.

Miscellaneous

Codes

ICD9-CM

359.1 Duchenne muscular dystrophy

Patient Teaching

Genetic counseling is important, to warn of the risk of additional affected infants.

FAQ

Q: What is the benefit of scoliosis surgery in patients with Duchenne muscular dystrophy?

A: It improves sitting balance and prevents discomfort that develops as the spine collapses.