Eletroneuromiografia Flashcards
Quais os objetivos da eletroneuromiografia?
Purpose of electromyography (EMG)/nerve conduction studies (NCS): (1) Localization, (2) fiber type involved (mot/sens/both), whether dz is axonal or demyelinating, (3) determine injury extent, (4) determine dx & tx.
Quais as contra-indicações a ENMG?
Cautions w/ EMG/NCS: (1) Bleeding disorders/coagulopathy, (2) contraindicated w/ cardiac defi brillators, (3) caution w/ pacemaker: no electrical stimulation over pacemaker.
O que não é visto adequadamente na ENMG?
Records large myelinated fi bers. Small myelinated & unmyelinated fi bers (autonomic & somatic pain nerves) are not as well recorded by this test. Sensory NCS SNAP: Represents sum of individual SNAPs. May be nl in neuropathies affecting only small fi bers In lesions proximal to dorsal root ganglia, SNAPS are nl b/c dorsal root ganglia & peripheral axon are intact
Logo, ENMG não descarta doença de fibras finas.
Quais as definições da ENMG?
Most common NCS: Compound muscle action potential (CMAP), sensory nerve action potential (SNAP), F-wave, H-refl exes. Defi nitions: Conduction velocity: Speed in the fastest conducting nerve fi bers; Latency: Time from stimulation to initial defl ection of the CMAP or SNAP; Amplitude of CMAP or SNAP: Distance from baseline to negative peak (upward); Duration: Time from initial defl ection from baseline to return; Antidromic: Stimulating toward the sensory receptor; Orthodromic: Away from the sensory receptor
O que são a onda F e o reflexo H?
# Late responses: F-wave & H-reflex are used to assess the proximal nerve segments. # F-wave: Pathway: antidromic activation of motor neurons → anterior horn cells → orthodromic impulses traveling back along motor axons; response involving motor fi bers only; may be absent in early Guillain-Barré synd. (initial demyelination may be only proximal). # H-refl ex: Pathway: sensory Ia afferent, synapses → back down efferent α motor neuron. Tests some of the same fi bers as ankle jerk, useful in assessing for S1 radiculop Perda da onda F é o achado mais precoce da SGB, forma AIDP.
Quais os componentes da ENMG?
Insertional activity: Electrical activity associated w/ inserting or moving the needle
- Normal (nl): Lasts few hundred milliseconds
- Decreased insertional activity: ↓ Electrical activity on needle insertion & movement. Occurs w/ atrophied muscle.
- Increased insertional activity : Defi ned as electrical activity lasting longer than 300 ms. Occurs w/ neuropathic & myopathic conditions & is characterized by the presence of positive sharp waves & fi brillation potentials on insertion
Examination of muscle at rest: Once the needle is in the muscle, evaluate for spontaneous activity. Nl muscle should not have activity at rest. Spontaneous activity typically means that there is pathology. Several types:
- Positive sharp waves: Brief init + burst, then long negative phase. In neuropathic & myopathic states. Equiv to fi brillation potentials: occur when needle tip in muscle fi ber.
- Fibrillation potentials: Spontaneous depol of muscle fi bers, which are fi ring autonomously. Also occur in presence of impaired innervation. Sound like “raindrops hitting a tin roof.” Occur in neuropathic & myopathic states.
- Complex repetitive discharges: Groups of spont fi ring action potentials; appear as runs of simple or complex spike patterns. Looks like a “muscular arrhythmia.” Occur in neuropathic & myopathic states, usually indicate longstanding injury (>6 mo).
- Myotonic discharges : Action potentials of muscle fi bers fi ring in a prolonged fashion, “Diver bomber” sound. Occur in myotonic dystrophy, myotonia congenita, paramyotonia congenita, acid maltase defi ciency, polymyositis, myotubular myopathy, hyperkalemic periodic paralysis, chronic radiculopathies, & neuropathies.
- Myokymic discharges : Groups of spontaneous motor unit potentials w/ a regular fi ring pattern & rhythm. Sounds like “soldiers marching.” May be seen in MS, Bell’s, polyradic. Clinical myokymia is described as “worm-like” movement of muscle. This is more often associated w/ neuromyotonic discharges on EMG.
Analyzing the motor unit: Analyze the MUAP morphology while pt contracts muscle slightly. Assess amplitude, rise time, duration, & phases. ↓ amplitude may be seen in myopathy. ↑ duration in neuropathic processes while ↓ duration occurs in myopathic processes. ↑ phases (polyphasia) in neuropathic processes.
Recruitment: Defi ned as the orderly addition of motor units to ↑ the force of contraction. Neuropathic recruitment characterized by few motor units fi ring at ↑ rate. Seen in neuropathies, radiculopathies, motor neuron disease, nerve trauma. Myopathic processes exhibit early & ↑ recruitment.
Qual o padrão da ENMG na doença do neuronio motor?
Motor neuron disease: NCS: Sensory NCS are nl. CMAP amplitude ↓. Latency & conduction velocities are nl, except w/ severe axonal loss where there is mildly ↑ latency & decreased conduction velocity. EMG: ↑ spont activity: + sharp waves & fi brillation potentials. May see fascics, complex repetitive discharges. MUAPs may be of long duration, ↑ polyphasicity & large amplitude, indicating reinnervation. ↓ recruitment.
Qual o padrão da ENMG na doença do sistema nervoso central?
CNS disorders: NCS: Sensory & motor NCS are nl. EMG: MUAP morphology & recruitment are nl but there is ↓’d activation.
Qual o padrão das neuropatias na ENMG?
Dividimos em 2 padrões, axonal e desmielinizante: # Demyelinating: 2/2 lesions affecting myelin sheath, such as entrapment or compressive neuropathies, Charcot-Marie-Tooth, or demyelinating forms of Guillain-Barré syndrome: NCS : Slow conduction velocity (slower than 75% lower limit of nl) & prolonged latencies (>130% upper limit of nl). Conduction block: Focal demyelination so severe that action potential cannot propagate along that area. CMAP amplitude is ↓ by >50% from distal to proximal stimulation sites. EMG : Nl unless there is conduction block where there is decreased recruitment.
Axonal: 2/2 processes affecting nerve, typically caused by toxic, metabolic or genetic causes. NCS : CMAP amplitude may be ↓, depending on axonal injury severity. Conduction velocity & distal latency are nl or mildly slow. (Conduction velocities are never <75% of the lower limit of nl & distal latencies are not >130% of the upper limit of nl). EMG: Increased spontaneous activity w/ fi brillations & + sharp waves. MUAP morphology nl early on but after weeks-months, there may be ↑ duration, amplitude, & number of phases.
Quando devemos solicitar a ENMG, considerando os processos fisiopatológicos?
Points to consider when planning the timing of studies for peripheral nerves: Abnl spont activity takes days-weeks to be detected; SNAPs & CMAPs ↓ several days after nerve injury & may appear nl in the first 3–4 days; at day 3–10, Wallerian degeneration occurs; when estimating recov period for peripheral nerves, keep in mind that axons regrow at a rate of 1 mm/day.
Quais o padrão de miastenia gravis na ENMG?
Myasthenia gravis: Sensory NCS nl. Motor NCS nl. Repetitive nerve stimulation (RNS): Abnl in 50%–70% w/ generalized myasthenia but often nl in isolated ocular myasthenia. With 3 Hz RNS, >10% ↓ in CMAP amplitude. EMG: nl, or unstable or short, small, polyphasic MUAPs; single fi ber EMG: Jitter & blocking
Qual o padrão da ENMG no Eaton-Lambert e no botulismo, duas doenças da JNM não MG?
Lambert Eaton: Sensory NCS nl. Motor NCS: CMAP amplitudes are diffusely low or borderline at rest; rep stim: CMAP amplitude ↑ at 30–50 Hz RNS or after 10 s of exercise. EMG: Typically nl, although MUAP may be unstable, short & w/ small, polyphasic MUAPs. Single fi ber EMG: Jitter & blocking.
Botulism: Sensory NCS nl. Motor NCS: CMAP amplitudes diffusely ↓ or absent. Rep stim: facilitation after 30–50 Hz RNS or 10 s of exercise. EMG: Fibrillation potentials, + sharp waves. MUAPs may be unstable & short, small, & polyphasic. Nl or ↓ recruitment.
Qual o padrão miopático na ENMG?
Myopathy: NCS: Sensory NCS are nl. Motor NCS usually nl, except in cases of myopathy involving distal muscle where CMAP amplitude may be ↓. EMG: MUAPs typically short duration, small amp, & polyphasic w/ early recruitment. In infl am myopathies, may see ↑ spontaneous activity: + sharp waves, fi b potentials, myotonic disch, complex repetitive discharge.
Qual o padrão de radiculopatia na ENMG?
Radiculopathy: NCS: Sensory & motor NCS are typically nl, except in case of a severe radicular lesion causing Wallerian degen distal to the lesion where CMAP may be ↓; NCS are useful in radic primarily to exclude other dx, such as a peripheral neuropathy. H-refl ex: Assesses afferent & efferent S1 fi bers (similar to the ankle refl ex). Useful in distinguishing S1 from a L5 radic. EMG: Acute setting: fi brillation potentials & + sharp waves. Chronic setting: Abnl motor units, such as long duration or polyphasic motor units. Test two muscles supplied by the same root but different peripheral nerves, & one paraspinal muscle.
