Muscular Dystrophy Flashcards
What is the pathophysiology of Duchenne’s muscular dystrophy?
Patients with Duchenne’s muscular dystrophy produce an abnormal protein called dystrophin that is found near the sarcolemma of muscle cells.
What are the physical signs and symptoms of
Duchenne’s muscular dystrophy?
The initial signs of Duchenne’s muscular dystrophy are related to weakness in the proximal skeletal muscle groups and manifest as an alteration in gait, difficulty climbing stairs, and frequent falls. The progressive and symmetric deterioration in
muscle strength is associated with fatty infiltration of the muscles which results in pseudohypertrophy of the muscles.
What is the incidence of Duchenne’s muscular
dystrophy and what patient demographic does it
affect?
Duchenne’s muscular dystrophy occurs in 3 out of every 10,000 live male births. It is an X-linked recessive disorder that presents most commonly in children between the ages of 3 and 5 years. By age 12, most patients are confined to a wheelchair.
What is the most common form of muscular
dystrophy?
Duchenne’s muscular dystrophy is the most common and most severe form of dystrophy.
What is the most common cause of death in patients
with Duchenne’s muscular dystrophy?
Death is most often attributed to pneumonia, respiratory failure, or cardiac failure and usually occurs between the ages of 15 and 25.
What lab value is typically elevated in patients with
Duchenne’s muscular dystrophy?
Because the skeletal muscle cells are prone to necrosis, serum creatine kinase levels may be 20 to 100 times higher than normal.
What are the cardiac signs of Duchenne’s muscular
dystrophy?
Cardiac muscle is not spared in Duchenne’s muscular dystrophy. The degeneration of myocardial cells results in a short PR interval, tall R waves in V1, deep Q waves in the limb
leads, and sinus tachycardia. Papillary muscle dysfunction and decreased myocardial contractility can lead to mitral regurgitation and congestive heart failure.
What are the respiratory complications of
Duchenne’s muscular dystrophy?
Progressive respiratory muscle weakness predisposes the patient to respiratory insufficiency and recurrent pneumonia. Sleep apnea often develops and can result in pulmonary
hypertension and the development of kyphoscoliosis contributes to the already compromised respiratory state.
What are the general anesthetic implications of
Duchenne’s muscular dystrophy?
Gastric hypomotility and decreased laryngeal reflexes predispose the patient to pulmonary aspiration. Succinylcholine is contraindicated due to the risk for rhabdomyolysis, hyperkalemia, and cardiac arrest. They have an increased risk
for malignant hyperthermia, so regional anesthesia is preferred, but if a general anesthetic is undertaken, careful monitoring of capnography and temperature should be performed with
dantrolene readily available. The risk for postoperative pulmonary complications is high due to skeletal muscle weakness.
How does the patient with Duchenne’s muscular
dystrophy respond to succinylcholine and
nondepolarizing muscle relaxants?
Because of the risk of rhabdomyolysis, hyperkalemia, and risk of cardiac arrest, succinylcholine is contraindicated in patients
with Duchenne’s muscular dystrophy. Also, the risk of malignant hyperthermia is increased in these patients and general anesthesia is typically avoided. The response to NDMRs is normal.
What events would be most likely to induce myotonic contractions in a patient with myotonic dystrophy
In patients with myotonic dystrophy, myotonic contractions can be so severe that ventilation can become difficult. Agents that are associated with an increased risk of producing myotonic
contractions include succinylcholine, neostigmine, and physostigmine. Shivering associated with inhalation anesthesia can also induce myotonic contractions (small doses of meperidine can be administered to prevent this). The response
to nondepolarizing muscle relaxants appears to be normal, but shorter-duration agents such as cisatracurium are recommended. Reversal of NDMRs is not recommended. If myotonic contractions become severe, they can be treated with the injection of procaine directly into the muscle or by administering 300-600 mg of quinine hydrochloride intravenously. Regional anesthesia is not contraindicated, but does not necessarily relieve myotonic contractions.
