Neuromuscular Diseases Flashcards
Inflammatory Myopathies
-acquired diseases mostly autoimmune (polymyositis, dermatomysitis, inclusion body myosistis, sarcoidosis) or by infection (trichinosis)
What are metabolic myopathies caused by?
enzyme deficiencies that block metabolic pathways, depriving muscle cells of energy for muscle contraction and relaxation and to maintain membrane integrats
What happens during metabolic myopathies?
Breakdown (rhabdomyolysis) and excretion of muscle proteins in urine (myoglobinuria) when energy demands increase with exercise
Metabolic Myopathies?
disorders of glycogen, lipid metabolism, or disorders of mitochondrial respiratory chain
How do metabolic myopathies present?
- muscle weakness or exercise intolerance
- muscle pain
- myoglobinuria
Myotonic Dystrophy
-percussion and grip myotonia
-facial, neck, distal weakness
-autosomal dominant
-cataracts
-balding
-diabetes
-central sleep apnea
-megaesophagus, megacolon
-heart conduction defects
-mental retardation in newborns of MD moms
-genetic defect increases (increased CGT repeats)
chromosome 19
-proximal myotonic dystrophy is similar, but has proximal weakness & a different genotype (change in chromosome 3)
Myasthenia gravis
- autoimmune disease characterized by fluctuation muscle weakness
- weakness is caused by antibodies that bind and destroy muscle acetylcholine receptors
- Patients usually respond to anticholinesterase drugs, immunotherapy and thymectomy
- also perform repetitive stimulation test*
Tensilon/Edrophonium
Ach drug that produces rapid improvement of myasthenia gravis
Treatment of Myasthenia Gravis?
- ach drugs like pyridostigmine
- corticosteroids
- immunosuppressants (azathioprine, cyclophosphamide, mycophenolate mofeti)
- Thymectomy (if large)
- Plasma exchange (removes abs)
- Immunoglobulin infusions
Symptoms of Lambert-Eaton myasthenic syndrome?
- proximal limb weakness
- “fatigue” or fluctuation of symptoms
- difficulty rising from sitting position
- reduced ability to walk/climb
- dry mouth, metallic taste, anticholinergic symptoms
Signs of Lambert-Eaton myasthenic syndrome?
- proximal limb weakness (legs>arms)
- reduced muscle stretch reflexes
- transient improvement in muscle power following exercise
- minimal eyelid droop*
- small poorly reactive pupils
Gower’s Sign
-how a patient with proximal muscle weakness must get up
Myopathy pattern of weakness
proximal > distal
Neuromuscular junction pattern of weakness
proximal > distal
Polyneuropathy pattern of weakness
distal > proximal
When muscle looses innervation??
the muscle fibers become atrophic and angulated
-atrophic fibers stain dark
polyphasic
damaged individual fibers fire asynchronously
Myopathies as far as fibers go?
nromal # of motor neurons and axons, motor untis
-# of individual fibers that are nonfunctional
Myopathies
- decreased in the # of muscle fibers per motor unit
- During voluntary activity
- motor unit potentials are small in size and of short duration
- increased number of motor unit action potentials as compared to the strength of contraction
- decreased # of muscle fibers per motor unit
Myopathies: Signs & Symptoms
- proximal, symmetrical weakness
- normal sensation
- normal reflex
- elevated muscle enzyme in serum
- small motor unit potentials on EMG with normal or increased recruitment on maximal effort
- abnormal muscle biopsy, depending on the type of myopathy
Infantile Acid Maltase Deficiency
“floppy”
Congenital Myopathies
- “floppy” infants (weakness, hypotonia) at birth, central core disease, myotubular myopathy or rod myopathy and congenital muscular dystrophy
- hereditary
Muscular Dystrophies
PROGRESSIVE
- early childhood
- hereditary and progressive conditions
- some are caused by abnormalities or deficiencies of the muscle membrane or nuclear proteins
ex: Duchenne’s, Becker’s, limb girdle, fascioscapulohumeral and oculopharyngeal dystrophy’s - hereditary
Myotonic Dystrophies
PROGRESSIVE
- characterized by the presence of myotonia and weakness
ex: myotonic dystrophy and proximal myotonic myopathy - hereditary
Duchenne’s Muscular Dystrophy
Lethal Childhood Disorder
- abnormal gene, no dystrophin
- 1 in 3,500 male births
- progressive muscle weakness, pseudohypertryphy, abnormal heart, low IQ
Duchenne’s causes what about muscle?
- necrosis
- atrophy
- segmental fiber over-contraction
- connective tissue proliferatioin
Duchenne’s Signs/Symptoms
- winging of scapulae
- lordosis
- large calf muscles
What stain shows dystrophin?
immunoperoxidase
Becker’s Muscular Dystrophy
- some muscle fibers have protein
- Lordosis
- Calf hypertrophy
- present at older age
Endocrine Myopathies
proximal
- develop weakness in hyperparathyroidism
- Crushing’s disease and hypothyrodism
- select Type II muscle fiber atrophy
Toxic Myopathies
- ethanol
- anesthetics
- cholesterol-lowering agents
- glucocorticoids
- narcotics
- herbicides
- muscle fiber atrophy, vacuolization, myofibrillary degeneration, mitochondrial dysfunction, fiber necrosis*
Therapy of Lambert-Eaton Syndrome
-romoval of associated neoplasm
-“symptomatic” boost of neuromuscular transmission
Pyridostigmine-cholinesterase inhibitors
3,4-diaminopyridine
Immunosuppressive therapy
-high-dose, long term corticosteroids
-azathioprine
-plasmapheresis
