Neuromuscular Diseases Flashcards
(41 cards)
List five potential causes of upper motor neuron dysfunction.
Intracranial hemorrhage, stroke, CNS trauma, CNS tumor, and transverse myelitis.
Where are upper motor neuron lesions located anatomically?
Upper motor neuron lesions may include axons in the brain, through the spinal cord, and up to (but not including) the anterior horn cell.
Where are lower motor neuron lesions located anatomically?
Lower motor neuron lesions may occur in the anterior horn cells, peripheral nerves, neuromuscular junctions, and/or muscles.
A patient presents with weakness, muscle atrophy, fasciculations, fibrillations, hypotonia, and hyporeflexia. Does this patient have an upper or a lower motor neuron disorder?
Lower motor neuron
List five potential causes of lower motor neuron dysfunction.
Infection, Guillain-Barre syndrome, botulism, myasthenia gravis, and rhabdomyolysis.
What is the genetic inheritance pattern for spinal muscular atrophy?
It is an autosomal recessive disorder that maps to the SMN1 gene on chromosome 5q.
What is the characteristic pattern of muscle involvement in patients with spinal muscular atrophy?
Muscle weakness is symmetric, with the proximal muscles affected to a greater degree. The legs are more commonly affected than the arms.
Describe the typical presentation of spinal muscluar atrophy type 1.
This is the most severe form and presents at < 6 months of age with hypotonia and weakness, difficulty feeding, and tongue fasciculations. Most patients die by two years of age due to respiratory failure.
What is Werdnig-Hoffman disease?
This is another name for spinal muscular atrophy type 1, AKA severe infantile SMA.
Describe the typical presentation of spinal muscluar atrophy type 2.
Infants appear healthy at birth and achieve normal milestones, but then lose their milestones by 2 years of age. The majority die by 12 years of age. Weakness can be static for long periods of time and then progress with intercurrent illnesses.
Describe the typical presentation of spinal muscluar atrophy type 3.
Patients present between 2 and 17 years of age with a progressive inability to walk or stand unaided. The degree of deficit correlates with the age of symptom onset - the earlier the onset, the greater the deficit.
What is Kugelberg-Welander disease?
Spinal muscular atrophy type 3, AKA juvenile SMA.
What is the inheritance pattern for Duchenne muscular dystrophy?
DMD is an X-linked recessive disorder, with up to 30% of cases being caused by spontaneous mutations.
What gene and associated gene product are abnormal in patients with Duchenne muscular dystrophy?
DMD is caused by a mutation in the dystrophin gene and results in absent or deficient dystropin protein.
What is a common presentation for a boy with Duchenne muscular dystrophy?
Boys present between 2 and 6 years of age with frequent falling, a waddling gait, and toe walking. Classic exam findings include: a child with calf muscle pseudohypertrophy and the Gowers sign (using arms to climb up the legs when rising from a seated position on the floor).
What is the typical clinical progression for boys with Duchenne muscular dystrophy?
Affected boys usually lose the ability to walk by 12 years of age. Respiratory muscle weakness corresponds to gross motor weakness. Eventually, respiratory secretions can’t be handled and aspiration/infection commonly occurs. Cardiomyopathy is also a component of the disease. Respiratory failure is a common cause of death in these patients.
How is Duchenne muscular dystrophy diagnosed?
If DMD is clinically suspected, measuring a CK is the next step and will be elevated in patients with the disease. Diagnosis is then confirmed by identifying a mutation of the DMD gene. Muscle biopsy is only used to confirm diagnosis in patients with negative genetic testing.
How does Becker muscular dystrophy differ from Duchenne muscular dystrophy?
Becker resembles DMD but has a less severe course and later onset of symptoms. Diagnosis and management are the same as in DMD but Becker patients are able to retain ambulatory abilities after 15 years of age and life expectancy can be into the 4th or 5th decade.
What is myasthenia gravis?
Myasthenia gravis is a disorder of neuromuscular transmission. In patients with the disease, the post synaptic acetylcholine receptors are reduced in number. This results in muscle weakness that worsens as the day goes on (and acetylcholine stores are depleted trying to overcome the decreased number of receptors).
What is transient neonatal myasthenia gravis?
This disorder occurs when the newborn is exposed to transplacental passage of maternal acetylcholine receptor antibodies. The neonate presents within 72 hours of birth with hypotonia, weak cry, difficulty feeding, facial weakness, and ptosis. They eventually develop respiratory compromise as well, but the disorder resolves in 2-6 weeks as the maternal antibodies clear from the infant’s system.
How does juvenile myasthenia gravis present?
The disease progresses gradually, with worsening muscle weakness, fatigability, and respiratory compromise. Muscle weakness is exacerbated by repetitive muscle use. Ocular muscles are involved, resulting in ptosis and ophthalmoplegia.
How is myasthenia gravis diagnosed?
Diagnosis is made by demonstrating the presence of acetylcholine receptor antibodies (AChR-Ab) in the patient.
How is myasthenia gravis treated?
Pyridostigmine (anticholinesterase - increases the concentration of acetylcholine at the receptor site). Most patients also require immunosuppression. Thymectomy induces remission in as many as 50-60% of patients. Plasmapheresis or IVIG may be utilized for short-term amelioration of worsening symptoms.
How does Guillan-Barre syndrome classically present?
Look for a child with acute paralysis, beginning with weakness of the legs, followed by progressive paralysis that moves upward throughout the body. It can progress to involve the respiratory muscles and the cranial nerves. Tendon reflexes are absent. Sensory losses are rare and are restricted to the vibratory and position sense.
