Neuromuscular Disorders - Ifergane Flashcards
Table of clinical features of neuromusclular disorders: how are the weakness, fatigability, atrophy, tendon reflexes sensory symptoms and sensory findings in injury in each place (Anterior Horn, Nerve, NMJ and Muscle)?
How is electroyography performed and how are results interpreted?
Electrode (by needle) placed on/in peripheral muscles. Stimulates external nerve. Currents signal a speaker. Single fiber targets signal of only one motor unit.
Recording is of compound muscle action potential. Higher voltage yields a higher reaction. More motor units are stimulated up to a supramaximal stimulation.
Latency is the time in which the nerve conducts and the neuromuscular transmission. (Velocity of a nerve is 40-50 m/s).
Axonal lesions indicate fewer nerves are responding and so the amplitude is reduced.
Demyelination lesions indicate slower conduction (sometimes decreased amplitude due to discoordination and conduction block).
What are the EMG signals in the seven causes of muscle weakenss?
1. Insertional activity:
Normally some static
LMN disease (anterior horn cells: polio, ALS; peripheral nerves: neuropathy, trauma): increased insertional activity
UMN disease (cerebral cortex: CVA, neoplasm, trauma; corticospinal tract: syringomyelia, neoplasm, trauma): normal
Myogenic lesion (neuromuscular juction: myasthenia gravis; muscle membrane: myotonia; contractile mechanism: muscular dystrophy): normal (except myotonia: with myotonic discharge and Polymyositis: increased )
2. Spontaneous activity:
Normally minimal
LMN disease: rain on a tin roof from injury potentials
UMN: normal
Myogenic: normal (except polymyositis: with fibrillation and positive waves)
3. Motor unit potential:
Normally .5-1mV over 5-10ms
LMN disease: wide units with limited recruitment, high amplitude from lack of compensation
UMN: normal
Myogenic: small unit with early recruitment (except myotonic: discharge and polymyositis: small unit early recruitment)
4. Interference pattern:
Normal lack of identification of individual potentials with full interference at normal amplitude
LMN: Reduced interference with fast firing rate of fewer motor units
UMN: reduced with slow firing rate
Myogenic: full interference with low amplitude
What is the difference between spasticity and rigidity?
Spasticity is like a swiss army knife: stiff to open and then lets go. Also urinary retention.
Rigidity: resistance all the way both ways
What are the types of lower motor neuron disease?
- Anterior horn
Polio
ALS - Motor root (at exit from SC)
Plexus (brachial or lumbosacral) - Peripheral nerves
GBS (>90% of acute neuropathy, Autoimmune cause)
What are the differential diagnoses of distal polyneuropathy?
What are the types of myositis?
What is CIDP (Chronic Inflammatory Demyelinating Polyneuropathy) and what are its major features?
- AKA Chronic GBS
- High protein levels in CHF
- Longer than 8 weeks (otherwise Guillen Barre), also more muscle atrophy
How are the types of myositis (dermatomyositis, polymyositis, and inclusion body myositis) distinguished (table)?
What are the main features of Charcot Marie Tooth disease?
- Chronic, congenital often asymptomatic
- Motor and sensory- symmetric, slowly progressive distal muscular atrophy of legs and feet and eventually the hands
- Very common, typically presents in adolescence
- CMT-2 is the only axonal motor neuropahy version, others are demyelinating
What are the treatments for neuropathic pain?
Anticonvulsants: Carbamazepine, gapapentin and pregabalin
Antidepressants: MAOIs, Serotonin, norepinephrine, tricyclic antidepressants
Opiates: morphine, etc.
What are the differential diagnoses of myalgia?
1: Febrile
Drug induced-statins
Infection
Trama (focal)
Rhabdomyolysis (check CPK, myoglobin)
What are the common features of common muscular dystrophies?
Facioscapulohumeral Muscular Dystrophy:
- Asymmetrical
- Appears by age 20
- 15% become wheelchair bound
- Autosomal dominant
Duchenne and Becker Muscular Dystrophy
- Childhood onset of proximal muscle weakness including neck flexors, no oscular/bulbar invovlement
- Dystrophin dysfunctional
- Duchenne is wheelchairbound by adolescence
What are the common features of myotonic dystrophy?
- Autosomal dominant inherited skeletal muscle disorder
- Systemic disorder: cataracts, ptosis, arrhythmias, dysphagia (esophageal myotonia), insulin resistance, testicular atrophy, frontal balding, changes in affect, personality and motivation, cognitive dysfunction
- Defect in unstabele CTG expansion in DMPK gene or CCTG expansion in ZNF9 gene
- Presenting symptoms weakness and stiffness of distal muscles, with possible action and percussion myotonia
- Distal weakness before proximal
What are the main clinical features in myesthenia gravis?
- Immunologic disorder with antibodies against postsynaptic nicotinic acetylcholine receptor (nAChR)
- Most common disorder of neuromuscular junction transmittion.
- More common in women in 20-30s, in men in 70-80s
- Fluctuating symptoms
- Treated with acetylcholinesterase inhibitor (Tensilon, doesn’t cross BBB)
- EMG: repetitive stimulus 3s-1 sequences shows decreasing amplitude with each stimulation. Typical variable difference between two spikes- 2 muscle fibers of the same motor unit-jitter.
- Treatment: AChesterase inhibitors, steroids, immunosuppressive therapy
