Neuromuscular Disorders Flashcards
What is Myasthenia Gravis (MG)?
MG is an autoimmune neuromuscular junction disorder characterized by muscle weakness and fatigability due to autoantibodies against acetylcholine receptors.
What are the two major neuromuscular disorders covered in this document?
Myasthenia Gravis and Muscular Dystrophy.
What is the pathophysiology of Myasthenia Gravis?
Autoantibodies attack acetylcholine receptors at the neuromuscular junction, reducing signal transmission and causing muscle weakness.
What are the three components of the neuromuscular junction?
Presynaptic membrane, synaptic cleft, and postsynaptic membrane.
What percentage of MG patients have anti-acetylcholine receptor (AChR) antibodies?
80-90% of generalized MG and 50-60% of ocular MG cases.
What is seronegative MG?
MG in which patients lack detectable AChR antibodies, often associated with MuSK antibodies.
What thymic abnormalities are common in MG?
Thymic hyperplasia (70%) and thymoma (10%).
What is the main clinical feature of MG?
Muscle weakness that worsens with activity and improves with rest.
Which muscles are most commonly affected in MG?
Extraocular muscles, bulbar muscles, neck, and shoulder girdle muscles.
What is the first symptom in most MG patients?
Ptosis (drooping eyelid) and diplopia (double vision).
How does MG affect bulbar muscles?
It causes dysphagia (difficulty swallowing) and dysphonia (voice changes).
What is the Osserman classification for MG severity?
0 - Asymptomatic, 1 - Ocular symptoms, 2 - Mild generalized weakness, 3 - Moderate generalized weakness/bulbar involvement, 4 - Severe generalized weakness/respiratory dysfunction.
What is Lambert-Eaton Myasthenic Syndrome (LEMS)?
A presynaptic disorder of neuromuscular transmission affecting voltage-gated calcium channels, often associated with small cell lung cancer.
How does botulism affect neuromuscular transmission?
It blocks acetylcholine release, leading to paralysis and affecting pupillary responses.
What is the Tensilon test?
A test using edrophonium chloride (a short-acting acetylcholinesterase inhibitor) to temporarily improve muscle strength in MG.
What is the Ice-Pack Test?
A test where an ice pack is placed over the eyelid to improve ptosis in MG patients.
Which antibodies are found in MuSK-associated MG?
Muscle-specific tyrosine kinase (MuSK) antibodies.
What is the gold standard electrophysiologic test for MG?
Single Fiber EMG (SFEMG), which detects increased jitter and neuromuscular transmission defects.
Why should MG patients undergo chest imaging?
To check for thymoma or thymic hyperplasia.
What is the first-line treatment for ocular MG?
Anticholinesterase inhibitors like pyridostigmine or neostigmine.
What is the first-line treatment for generalized MG?
Corticosteroids (prednisolone) with or without immunosuppressants like azathioprine or mycophenolate mofetil.
What is the role of thymectomy in MG?
Thymectomy is recommended for patients with thymoma and can improve outcomes in non-thymomatous generalized MG.
What are the triggers for Myasthenic Crisis?
Respiratory infections, stress, surgery, pregnancy, and certain medications (aminoglycosides, beta-blockers).
What is Myasthenic Crisis?
An acute exacerbation of MG leading to severe weakness of respiratory and upper airway muscles, requiring ventilatory support.
How is Myasthenic Crisis managed?
Intubation, plasmapheresis, or intravenous immunoglobulins (IVIG).
What is a Cholinergic Crisis?
Excessive acetylcholinesterase inhibitor use causing continuous depolarization, leading to weakness and autonomic symptoms like salivation and diarrhea.
How is a Cholinergic Crisis differentiated from a Myasthenic Crisis?
The edrophonium test improves Myasthenic Crisis but worsens Cholinergic Crisis.
What are neuromuscular blocking agents that worsen MG?
Succinylcholine and non-depolarizing muscle relaxants (e.g., vecuronium).
What is Muscular Dystrophy?
A group of genetic disorders causing progressive muscle weakness due to defective muscle proteins.
What is the most common type of Muscular Dystrophy?
Duchenne Muscular Dystrophy (DMD).
What is the genetic cause of Duchenne Muscular Dystrophy?
Mutations in the dystrophin gene on the X chromosome.
What is the difference between Duchenne and Becker Muscular Dystrophy?
DMD has little to no dystrophin, while BMD has reduced but functional dystrophin.
What is Gower’s Sign?
A sign of proximal muscle weakness where patients use their hands to push on their legs to stand up.
What is the inheritance pattern of Duchenne Muscular Dystrophy?
X-linked recessive.
What are the common types of Muscular Dystrophies?
Duchenne, Becker, Limb-Girdle, Facioscapulohumeral, and Myotonic Dystrophy.
What are early symptoms of Duchenne Muscular Dystrophy?
Delayed motor milestones, difficulty climbing stairs, frequent falls, and calf pseudohypertrophy.
What is the main cause of death in Duchenne Muscular Dystrophy?
Respiratory failure or cardiomyopathy.
What is the main diagnostic test for Duchenne Muscular Dystrophy?
Genetic testing for dystrophin mutations.
Which enzyme is elevated in Duchenne Muscular Dystrophy?
Creatine Kinase (CK).
What is the treatment for Duchenne Muscular Dystrophy?
Corticosteroids (prednisolone), physical therapy, and supportive care.
What are common complications of Muscular Dystrophy?
Scoliosis, respiratory failure, cardiac dysfunction, and contractures.
What is Myotonic Dystrophy?
A muscular dystrophy characterized by progressive weakness and myotonia (delayed muscle relaxation).
What are the systemic features of Myotonic Dystrophy?
Cataracts, cardiac conduction defects, insulin resistance, and cognitive impairment.
What is the most common adult-onset Muscular Dystrophy?
Myotonic Dystrophy Type 1 (DM1).
How is Muscular Dystrophy managed?
Supportive care, corticosteroids, physical therapy, and assistive devices.
What are some genetic mutations associated with Limb-Girdle Muscular Dystrophy?
Dysferlin, sarcoglycan, and calpain mutations.
How is Facioscapulohumeral Muscular Dystrophy inherited?
Autosomal dominant.
What is the prognosis of Duchenne Muscular Dystrophy?
Patients often require wheelchairs by their teens and have a reduced lifespan, usually due to respiratory or cardiac failure.
How does Becker Muscular Dystrophy differ in prognosis?
Becker Muscular Dystrophy has a later onset and milder progression compared to Duchenne.
