Myasthenia Gravis Overview

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Questions and Answers

What is the primary mechanism of injury in Myasthenia Gravis?

IgG antibodies destroy post-junctional nicotinic ACh receptors (correct)

Absence of myelin sheath around nerve fibers

Destruction of pre-junctional acetylcholine receptors

Overactivity of acetylcholine in the synaptic cleft

When does muscle weakness typically worsen in patients with Myasthenia Gravis?

After periods of rest

In the morning after waking up

Later in the day or with exercise (correct)

After physical relaxation

What surgical intervention may provide symptom relief for Myasthenia Gravis?

Laminectomy

Thymectomy (correct)

Appendectomy

Cholecystectomy

What are early signs and symptoms associated with Myasthenia Gravis?

Diplopia and ptosis Signup and view all the answers

Which situation is known to exacerbate the symptoms of Myasthenia Gravis?

Surgical and psychological stress Signup and view all the answers

What are the considerations for neonates born to mothers with Myasthenia Gravis?

They may experience weakness due to maternal antibodies Signup and view all the answers

What test is commonly used to diagnose Myasthenia Gravis?

Tensilon test (edrophonium) Signup and view all the answers

What is considered the first-line treatment for Myasthenia Gravis?

Oral pyridostigmine Signup and view all the answers

What is the response of patients with Eaton-Lambert Syndrome to anticholinesterase reversal?

Reversal may be inadequate despite proper dosing Signup and view all the answers

What immunologic problem is associated with Guillain-Barre Syndrome?

An attack on myelin in peripheral nerves Signup and view all the answers

Which of the following is a common symptom of Guillain-Barre Syndrome?

Flaccid paralysis that ascends bilaterally Signup and view all the answers

What is a common co-morbidity associated with Eaton-Lambert Syndrome?

Small-cell carcinoma of the lung Signup and view all the answers

What commonly precedes the paralysis seen in Guillain-Barre Syndrome?

A flu-like illness Signup and view all the answers

Which option describes patients' sensitivity in Eaton-Lambert Syndrome?

Sensitive to both succinylcholine and non-depolarizers Signup and view all the answers

What is a long-term consequence that can be associated with Guillain-Barre Syndrome?

Chronic pain and fatigue Signup and view all the answers

What effect do volatile anesthetics have during surgical procedures?

Enough muscle relaxation for most procedures Signup and view all the answers

What is the recommendation for patients with Familial Periodic Paralysis when placed on cardiopulmonary bypass?

They should remain normothermic. Signup and view all the answers

Which medication should be avoided in patients with Hypokalemic Familial Periodic Paralysis?

Succinylcholine Signup and view all the answers

What triggers malignant hyperthermia in susceptible individuals?

Halogenated anesthetic agents Signup and view all the answers

Which medication is safe to administer to Hyperkalemic Familial Periodic Paralysis patients?

Nondepolarizers Signup and view all the answers

How does Familial Periodic Paralysis impact the metabolism of succinylcholine?

It can cause hyperkalemia in patients. Signup and view all the answers

Which type of neuromuscular blockers (NMBs) are safe for patients with Familial Periodic Paralysis?

Nondepolarizing NMBs Signup and view all the answers

What is a significant characteristic of the ryanodine receptor in relation to malignant hyperthermia?

It releases excessive amounts of calcium into the cell. Signup and view all the answers

Which medication is categorized as unsafe for patients with Hyperkalemic Familial Periodic Paralysis?

Succinylcholine Signup and view all the answers

What effect does the SERCA2 pump have on excess Ca+2 in the cell?

It consumes ATP and increases metabolic activity. Signup and view all the answers

Increased intracellular calcium in the myocyte is most likely to cause which of the following consequences?

Potassium and myoglobin leak into systemic circulation. Signup and view all the answers

Which of the following diseases is definitively associated with malignant hyperthermia (MH)?

King-Denborough syndrome Signup and view all the answers

What is a notable characteristic of the association between Duchenne muscular dystrophy and MH?

Halogenated agents can trigger an MH-like syndrome. Signup and view all the answers

What initial treatment should be administered to a patient with Duchenne muscular dystrophy who experiences cardiac arrest?

Calcium chloride Signup and view all the answers

Which indicator is considered the most sensitive for detecting malignant hyperthermia?

Increased EtCO2 disproportionate to minute ventilation Signup and view all the answers

Which of the following is an early sign of malignant hyperthermia?

Tachycardia Signup and view all the answers

What is a potential consequence of the sarcolemma breaking down during an episode of increased intracellular calcium?

Leaking of potassium and myoglobin Signup and view all the answers

What is one of the benefits of hyperventilation?

Facilitates CO2 elimination Signup and view all the answers

What should be administered to treat hyperkalemia?

Insulin with D50 Signup and view all the answers

Which of the following is a complication of co-administering a calcium channel blocker with dantrolene?

Life-threatening hyperkalemia Signup and view all the answers

What is a recommended treatment to correct lactic acidosis?

Sodium bicarbonate IV Signup and view all the answers

What is the purpose of maintaining urine output greater than 2 mL/kg/hr?

To protect against renal injury from free myoglobin Signup and view all the answers

What symptom does the absence of dystrophin cause during muscle contraction?

Destabilization of the sarcolemma Signup and view all the answers

Which treatment would be appropriate for a patient requiring cooling?

Cold fluid lavage Signup and view all the answers

What is an indicator of impending demise in acute conditions?

Disseminated intravascular coagulation Signup and view all the answers

Study Notes

Myasthenia Gravis (MG)

Pathophysiology: IgG antibodies destroy post-junctional nicotinic acetylcholine receptors at the neuromuscular junction (NMJ), causing skeletal muscle weakness.
Weakness worsens later in the day or with exercise; rest improves function.
Thymectomy may relieve symptoms.
Signs and symptoms: Diplopia, ptosis (earliest), bulbar muscle weakness (dysphagia, dysarthria, drooling), dyspnea, proximal muscle weakness.
Exacerbating factors: Pregnancy, infection, electrolyte abnormalities, stress, aminoglycoside antibiotics.
Neonatal considerations: Maternal anti-AchR IgG antibodies cross the placenta, causing neonatal weakness.
Diagnosis: Edrophonium (Tensilon) test; improved strength suggests MG, worsening suggests cholinergic crisis.
Treatment: Anticholinesterases (pyridostigmine), immunosuppressants (corticosteroids, cyclosporine, azathioprine, mycophenolate), thymectomy, plasmapheresis.

Eaton-Lambert Syndrome

Associated with small-cell lung carcinoma. Consider in patients with suspected lung cancer undergoing relevant procedures.
Patients are sensitive to succinylcholine and non-depolarizing neuromuscular blockers (NDMBs). Volatile anesthetics usually provide sufficient muscle relaxation.
Reversal with anticholinesterases may be inadequate.

Guillain-Barré Syndrome (GBS)

Pathophysiology: Immunologic assault on myelin in peripheral nerves, disrupting action potential conduction.
Often preceded by a flu-like illness (1-3 weeks prior). Common etiologies include Campylobacter jejuni, Epstein-Barr virus, CMV, vaccinations, surgery, and lymphoma.
Signs and symptoms: Flaccid paralysis (distal to proximal, bilateral), intercostal muscle weakness (impaired ventilation), facial and pharyngeal weakness (dysphagia), sensory deficits (paresthesias, numbness, pain).

Familial Periodic Paralysis (FPP)

Hypokalemic FPP: Avoid glucose-containing solutions, potassium-wasting diuretics, beta-2 agonists, and succinylcholine. NDMBs and acetazolamide are safe. Possible association with malignant hyperthermia (MH), but muscle rigidity may occur without the metabolic changes seen in MH.
Hyperkalemic FPP: Avoid succinylcholine and potassium-containing solutions. Glucose-containing solutions, potassium-wasting diuretics, beta-2 agonists, NDMBs, and acetazolamide are safe. Succinylcholine use is risky due to potential for hyperkalemia.
NDMBs are safe for both types, but patients may be sensitive; short-acting agents are best.

Malignant Hyperthermia (MH)

Triggers: Halogenated anesthetic agents and succinylcholine.
Pathophysiology: Defective ryanodine receptor (RYR1) causes excessive calcium release from the sarcoplasmic reticulum, leading to sustained contraction, ATP depletion, increased oxygen consumption and CO2 production, acidosis, rhabdomyolysis, and hyperkalemia.
Consequences of increased intracellular calcium: Rigidity, accelerated metabolism, increased oxygen consumption and CO2/heat production, acidosis, sarcolemma breakdown, potassium and myoglobin release.
Associated diseases: King-Denborough syndrome, central core disease, multiminicore disease.
Duchenne Muscular Dystrophy (DMD) association: An MH-like syndrome can occur due to rhabdomyolysis (not true MH). Avoid halogenated agents and succinylcholine; use total intravenous anesthesia (TIVA).
Treatment of cardiac arrest in DMD patients: Treat as severe hyperkalemia with calcium chloride.
Most sensitive indicator: EtCO2 rising disproportionately to minute ventilation. Hyperthermia is a late sign.
Signs and symptoms: Early: Tachycardia, tachypnea, hyperventilation; Intermediate: Muscle rigidity, increased temperature, metabolic acidosis; Late: Severe hyperthermia, cardiac arrhythmias, rhabdomyolysis, disseminated intravascular coagulation (DIC).
Treatment: 1. Discontinue triggering agents; 2. Hyperventilate with 100% O2; 3a. Change anesthesia circuit and vaporizers if available; 3b. Apply charcoal filter to inspiratory/expiratory ports; 4. Administer dantrolene (or Ryanodex); 5. Cool the patient (<38° C); 6. Correct acidosis with sodium bicarbonate; 7. Treat hyperkalemia (CaCl2, insulin/D50, hyperventilation); 8. Protect against dysrhythmias (procainamide, lidocaine); 9. Maintain urine output (>2 mL/kg/hr) to prevent renal injury; 10. Monitor coagulation.

Duchenne Muscular Dystrophy (DMD)

Pathophysiology: Absence of dystrophin destabilizes the sarcolemma, increasing membrane permeability during muscle contraction.

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Description

This quiz covers the key aspects of Myasthenia Gravis (MG), including its pathophysiology, symptoms, diagnosis, and treatment options. Test your understanding of how MG affects skeletal muscle function and the factors that exacerbate this condition. Explore the critical concepts essential for recognizing and managing MG.