Ch. 10 Electrodiagnostic medicine II: Clinical Evaluation & Findings Flashcards
What is an H-reflex?
Electrophysiologically recorded Achilles muscle stretch reflex
How is an H-reflex generated?
Recording over the gastroc and soleus muscles and stimulating the tibial nerve in the popliteal fossa
Describe the stimulus needed to generate an H-reflex
Stim duration of 1 ms
Inc by 3-5 mA increments
Freq of <1/second
What does an abnormal H-reflex indicate?
Lesions alone sciatic nerve, lumbosacral plexus or S1 nerve root
What is a F-wave?
Late responses involving motor axons and axonal pool at the spinal cord level
How are F-waves elicited?
With maximal stim of the median, ulnar, peroneal or tibial nerves
What are the four types of needle examination during EMG?
- Insertional activity
- Spontaneous activity
- Morphology and size of motor units
- Motor unit recruitment
How is insertional activity examined?
Briefly inserting needle through muscle and observing amount and duration of electrical activity
When is decreased insertional activity seen?
In atrophied muscle or fatty tissue
What is considered increased insertional activity?
Activity lasting >300 ms after needle stops advancing
What is spontaneous activity?
Electrical discharges occurring after needle movement has stopped
Describe the appearance of an end-plate potential
Biphasic Initial negative (upward) deflection Fire irregularly Sputtering sound Assoc w/ pain
Describe the shape of a PSW
Biphasic
Describe the shape of a fibrillation potential
Triphasic
Describe grade 1+ spontaneous potentials
Transient but reproducible trains of discharges after moving the needle in more than one site or quadrant
Describe grade 2+ spontaneous potentials
Occasional spontaneous potentials >2 diff quadrants
Describe grade 3+ spontaneous potentials
Spontaneous potentials present in all quadrants
Describe grade 4+ spontaneous potentials
Abundant spontaneous potentials nearly filling the screen in all 4 quadrants
What is a polyphasic potential?
> 4 phases
What is a serrated potential?
Same clinic relevance as polyphasic with many turns that do not cross baseline
What are polyphasic potentials associated with?
Reinnervation of denervated motor units when duration is inc or myopathies and NMJ d/o when duration is short
What is seen on EMG with full force muscle contractions?
Screen filled w/ overlapping motor units making it impossible to assess individual motor units
What is seen on EMG with low force muscle contractions?
1 or 2 units firing at ~10Hz
What is reduced recruitment?
Firing ratio of highest firing rate to number of motor units in 100 ms is >10
What does reduced recruitment indicate?
Motor axonal loss or function drop out from conduction block
What is early or myopathic recruitment?
Many motor units recruited to generate a low level of force
What does early recruitment indicate?
Myopathy or NMJ disorder
What diseases are complex repetitive discharges seen in?
Polymyositis Limb girdle dsytrophy Myxedema Schwartz-Jampel synd Spinal muscular atrophy Amyotrophic lateral sclerosis Hereditary and chronic neuropathies Carpal tunnel synd
Which normal muscles are complex repetitive discharges seen in?
Iliopsoas
Biceps brachii
What diseases are Myokymic discharges seen in?
Multiple sclerosis Brainstem neoplasm Polyradiculopathy Bell pasly Radiaton plexopathy Chronic nerve compression Rattlesnake venom
What do complex repetitive discharges sound like?
Machine-like discharge
What do myokymic potentials sound like?
Marching soldiers
What do myotonic potentials sound like?
Diver bombers
What diseases are myotonic potentials seen in?
Myotonic dystrophy Myotonia congenita Paramyotonia Polymyositis Acid maltase def Hyperkalemic periodic paralysis Chronic radiculopathy/peripheral polyneuropathy
When should single fiber EMG’s be performed?
Neuromuscular disorders
Myasthenia gravis
Lambert-Eaton synd
What is a hallmark finding of Lambert-Eaton synd?
Marked facilitation of the CMAP >400% of baseline amp after brief contraction
What is Martin-Gruber anastomosis?
Branch from median nerve, usually the AIN joins the ulnar nerve in the forearm
What is seen with Martin-Gruber anastomosis on Median nerve NCS?
Median CMAP is smaller with wrist stimulation than w/ proximal stimulatio
What is seen with Martin-Gruber anastomosis on Ulnar nerve NCS?
Larger amp w/ wrist stim than w/ below or above elbow stim
What is an accessory deep peroneal nerve?
Part of the deep peroneal nerve that remains with the superficial peroneal nerve and innervates the EDB after passing behind the lateral malleolus
What is seen on EDB NCS with an accessory deep peroneal nerve?
Stim at the fibular head yields a higher CMAP than ankle stim when recorded over EDB
How can an accessory deep peroneal nerve be stimulated?
Stim behind the lateral malleolus
What type of stimulating probe is needed for pediatric EDX?
Pediatric bipolar stimulating probe
What type of EMG needle should be used for pediatric patients?
Monopolar
What skin surface temperature is needed in pediatric EDX?
36-37 degrees C
Which children are at risk for malignant hyperthermia?
Children with neuromuscular diseases who are given halogenated anesthesia
Which muscles should be tested for spontaneous activity in infants?
Extensor muscles and intrinsic hand and foot muscles
Describe motor units in pediatric patients
Bi or triphasic
Amp 100-700 uV
Short duration 5-9 ms
Which muscles should be examined for motor unit morphology and recruitment in pediatrics?
Flexor muscles
What is repetitive nerve stimulation used to evaluate?
Pre and postsynaptic neuromuscular disorders
What is the MCC of generalized hypotonia?
Central nervous system d/o
What is the MC neuromuscular dx in hypotonic infants?
Spinal muscular atrophy
What obstetric causes are related to brachial plexopathies at birth?
Duration of labor
Shoulder dystocia
What is involved in Erb pasly?
Upper plexus and C5 or C6 roots
What is involved in Kumpke palsy?
Lower trunk, C8 or T1 roots
What are anatomic risk factors for brachial plexus injury?
Supracostoclavicular space narrowing with cervical ribs or fibrous bands
What is the MC entrapment neuropathy?
Carpal tunnel synd
What are causes of CTS?
Repetitive trauma
Obesity
Pregnancy
Lupus
What are sx of CTS?
Aching pain in the forearm and wrist
Insidious onset of tingling, parasthesias of thumb, index and long finger
Thenar weakness
Nocturnal pain
What is mild CTS?
Prolonged SNAP and/or slightly reduced SNAP amp