Exam Findings in Duchenne Muscular Dystrophy include: Gower's Sign, Lumbar Lordosis, & Calf Pseudohypertrophy.
Duchenne & Becker Muscular Dystrophies (the Dystrophinopathies)
Muscular Dystrophies
Dystrophinopathies (Duchenne, Becker):
We include a pathological slide of a muscle from an individual with Duchenne muscular dystrophy (DMD).
Overview
- X-linked, Recessive form of muscular dystrophy that affects boys and occurs from a genetic mutation that prevents the synthesis of dystrophin.
- Muscle is replaced with fatty and fibrous connective tissue, which presents with pseudohypertrophic muscles: muscles that are enlarged from fat and connect tissue (not muscle).
- Duchenne Muscular Dystrophy is a severe dystrophinopathy wherein children are non-ambulatory at ~ age 13 – pseudohypertrophy of calf muscles is a notable clinical finding.
- Becker Muscular Dystrophy is a less severe dystrophinopathy in that patients aren't non-ambulatory until ~ age 40.
- As a helpful mnemonic add the treatment adage that the goal of corticosteroids is to: Make Duchenne boys into Becker men.
Duchenne Muscular Dystrophy
- Most severe form
- Manifests in childhood with proximal weakness (especially calf hypertrophy)
- Loss of ambulation ~ age 13
Becker Muscular Dystrophy
- Less severe form
- Manifests in early teens
- Loss of ambulation ~ age 40
Genetic & Diagnostic Characteristics of Duchenne & Becker Muscular Dystrophies
- Genetics
- X-Linked, Recessive
- Dystrophin gene mutation that leads to reduction/absence of dystrophin protein with resultant sarcolemma damage
- Diagnosis: Elevated CK (~20,000), Dystrophin Gene Deletion
- Treatment: Corticosteroids
The following is adapted, with permission, From Robert J. Schwartzman, MD Neurologic Examination (2006) Massachusetts, USA: Blackwell Publishing.
Duchenne muscular dystrophy (DMD)
- Boys are usually noted to be weak at 2–3 years of age with primary difficulty with walking.
- They demonstrate a waddling gait at 3–6 years of age, and have difficulty with
- Lumbar lordosis and calf hypertrophy are common. The calf muscles have an unusual rubbery consistency to them. Pseudohypertrophy can be seen in gluteal, deltoid and masseter muscles as well as the calves.
- Early in the disease the process is true hypertrophy, but over time muscles are replaced by fat and connective tissue which gives them their rubbery consistency. Plantar flexors and inverters remain strong over the course of the disease while the anterior tibialis muscle weakens.
- Gower’s maneuver is common (patients use their hands to push up from the thighs)
- Neck flexor weakness is present at all stages of the illness.
- A child with DMD cannot lift the head against gravity, which distinguishes it from Becker muscular dystrophy (BMD) and outliers.
- Heel cord contractures result.
- Muscle strength decreases between 6 and 11 years and reflexes are hard to elicit in the following pattern: triceps > biceps > knees > brachioradialis and ankle.
- Joint contractures, cardiac and pulmonary diseases supervene and the patient is wheelchair-bound by age 12.
- Cranial and sphincter muscles are spared while heart muscle, brain and
Beck muscular dystrophy (BMD)
- Demonstrates a later onset of symptoms with a similar muscular pattern of weakness. Pelvic and thigh muscles are involved first although calf hypertrophy is also seen.
- These patients survive to adulthood and are ambulatory beyond 16 years of age.