Download EMG/ Nerve Conduction Studies

ELECTRODIAGNOSTIC TESTING:
BLIND SPOTS, PITFALLS, AND
OVERCALL
Timothy R. Dillingham, M.D.
William J. Erdman Professor and Chairman
Department of Physical Medicine and Rehabilitation
Chief Medical Officer
Penn Institute for Rehabilitation Medicine
The University of Pennsylvania
OBJECTIVES: LIMITATIONS, PITFALLS
• Understand the important limitations in
electrodiagnostic medicine
• Nerve conduction reference values not well
standardized
– Interrater reliability low without standards
• Understand EMG has modest sensitivity,
but very high specificity – complementary
to MRI
• Overcall in its many forms
– Polyphasics, excessive testing, poor technique
NERVE CONDUCTION
STUDIES
Nerve Conduction Challenges
with Performance
• Skin prep minimizes impedance missmatch
between active and reference electrodes
• Overstimulation of adjacent nerves
• Stimulus artifact – optimize ground
• Captured motor unit can look like a SNAP
– Repeatability over three tracings
– Be careful with averaging, can “Lock In”
artifact
NERVE CONDUCTION
PITFALLS
• Multiple Entrapments found, eg; median,
ulnar
– MOST LIKELY A POLYNEUROPATHY
– STUDY A LOWER LIMB
NERVE CONDUCTION
TESTING
– Too many tests, increasing probability of one
false positive
– If you do 7 tests; 16% chance of a false
positive
– Probability of TWO false positives with 7 tests
is 1%
• Two findings is MUCH more compelling for
a diagnosis
– Use caution with overcalling with just
one abnormality
NORMATIVE DATA:
REFERENCE VALUES
• No standardization in our field regarding
reference values and techniques for Nerve
conduction testing
• Older norms plagued by;
– Low sample sizes
– Statistics not matching non- Gaussian
distributions
– Analog machines
– Poor study designs
NORMATIVE DATA:
BETTER REFERENCE VALUES
AANEM NORMATIVE DATA TASKFORCE
• ALL YOU NEED TO KNOW:
• RALPH BUSCHBACHER, MD
• NORMATIVE STUDIES IN THE 1990’s
AND 2000’s
• TOWER ABOVE MOST OF THE
LITERATURE REGARDING NORMS
ELECTRODIAGNOSIS:
PITFALLS
EMG
• Motor units can look like PSWs depending
on geometric position of needle
• PSWs and FIBs are REGULARLY FIRING
POTENTIALS
• Don’t move the needle too quickly, thrust
and stop
• Caution calling radiculopathy based upon
polyphasicity
EMG
• Do not assess motor unit morphology in
PSM, no norms
• Cervical PSM low false positives IF:
• Lumbar PSM low false positives IF:
– IMPOSE CRITERIA OF REGULAR FIRING
• PSM - ONLY LOOK FOR: FIBS, PSW,
CRDs
PARASPINAL MUSCLE EMG:
PREVALENCE OF FIBRILLATIONS IN NORMALS
•
•
•
•
•
Dumitru, Diaz, and King (2001)
Prospective study 50 normals L4/L5 levels
Monopolar needle, recorded potentials
Examined firing rate and rhythm
Fibrillation inclusion criteria; regular firing
rate
• 4% false positive fibrillations in paraspinal
muscles
NEUROLOGICAL CONDITIONS MIMICKING
CERVICAL RADICULOPATHY
• Entrapment/Compression neuropathies
– Median, Radial, and Ulnar
• Brachial Neuritis
• Multifocal Motor Neuropathy
• Need Extensive EDX study to R/O other
conditions
• ALS if upper motor neuron signs and
atrophy/weakness
• Myopathy, Myasthenia Gravis
NEUROLOGICAL
CONDITIONS MIMICKING
LSR
• Diabetic Amyotrophy
• Mononeuropathies
– Femoral
– Tibial
– Common Peroneal
• Need Extensive EDX study
EMG SENSITIVITIES FOR
LUMBOSACRAL
RADICULOPATHIES
• Varies widely
• Ranges from about 50% to 80%
• Various diagnostic standards
Study
Sample
size
Gold standard
EMG
sensitivity %
Lumbosacral radiculopathy
Weber and Albert [55]
Nardin et al [28]
Kuruoglu et al [8]
Khatri et al [56]
Tonzola et al [57]
Schoendinger [58]
Knutsson [45]
Young et al [3]
Linden and Berlit [3]
42
47
100
95
57
100
206
100
19
Clinical+imaging HNP
Clinical
Clinical
Clinical
Clinical
Surgically proven
Surgically proven
Clinical an imaging
Myelography and CT
60
55
86
64
49
56
79
84
78
EMG SENSITIVITY FOR
CERVICAL
RADICULOPATHIES
• Varies widely
• About 50% to 70%
• Usually clinical and/or myelographic
Study
Lumbosacral spinal
stenosis
Hall et al [46]
Johnsson et al [59]
Sample
size
Gold standard
EMG
sensitivity %
68
64
Clinical+myelogram
Clinical+myelogram
92
88
18
77
24
14
20
20
108
Clinical
Intraoperative
Clinical+myelogram
Clinical
Clinical/radiographic
Clinical
Clinical
61
67
67
71
50
95
51
Cervical radiculopathy
Berger et al [60]
Partanen et al [61]
Leblhuber et al [9]
So et al [62]
Yiannikas et al [18]
Tackman and Radu [15]
Hong et al [63]
SPECIFICITY
Tong, Haig, Yamakawa, Miner. Amer J of PM&R 2006
• Assymptomatic volunteers 55 and older
• Standardized monopolar EMG with blinded researcher
– Five leg muscles and paraspinal muscles
• When only PSW and Fibs were considered abnormal
– By criteria: i)Two limb muscles plus PSM or ii)two
limb muscles or iii) one limb and PSM
– 100% specificity
• If use polyphasicity
– 97%, 90%, 87% specificity
• EMG has excellent specificity for LSR
CAVEATS AND
LIMITATIONS
• Needle EMG is not an effective screening
test alone (Radiculopathy)
• MRI better screen for structural causes
• Better specificity-Diagnosis confirmation
• Motor Axonal loss is necessary for fibs
• A purely sensory radiculopathy will not
result in FIBS on EMG
EMG
• Hard signs, better interrater reliability
– FIBS
– PSWs
– CRDs
• Softer signs, more tendency to overcall
– Polyphasicity
– Reduced recruitment
– Amplitudes of MUAPs
EMG
• Normative data for needle EMG are rare
and old
– Mostly for CONCENTRIC NEEDLES
– Monopolar needles – Chu textbook
• Wide range of normal variation. The
extremes are clearer
– Amplitudes over 8K with reduced recruitment
– Firing ratio of 20Hz
FALSE NEGATIVE (no fibs or PSW) ON
EMG IN RADICULOPATHY
• Sensory root involvement only
• Motor root involvement without axonal loss
– Demyelination, conduction block
• Motor axonal loss balanced with
reinnervation
MUSCLE INJURY CAUSING
FIBRILLATIONS
Partanen et al 1982 Muscle &
Nerve
• Study of 43 patients with EMG before and
after Muscle biopsy
• 50% had fibrillations 6-7 days after biopsy
• At 16 days 100% had fibrillations
• Fibrillations persisted up to 11 months post
biopsy
Symptom Duration is not Related to
Fibrillation Potentials
• Long held notion in the electrodiagnostic
literature regarding radiculopathies
• Paraspinal (PSM) muscles denervate first,
then more distal
• Reinnervation thought to occur first in PSM
then distal
• No evidence to support this model
SYMPTOM DURATION AND EMG FIBRILLATIONS
Dillingham et al, 1998, 1998, 2000; Pezzin et al 1999
• Four separate investigations
– Two retrospective (Cervical and Lumbosacral)
– Two prospective (Cervical and Lumbosacral)
• Probability of finding fibrillations in a muscle
(proximal or distal) was not related to
symptom duration.
• Simplistic model of symptom duration doesn’t
explain the complex pathophysiology of
radiculopathies and their EMG correlates
PROGRESSION OF CERVICAL SPONDYLOTIC CORD
COMPRESSION
Bednarik et al Spine 2004
• Symptomatic cervical radiculopathy and
EMG showing motor axonal loss in 2
myotomes predicted with 90% accuracy
those who progressed to symptomatic
myelopathy.
• Odds ratio 12.5 (p<0.001) for EMG
Needle electromyography predicts outcome
after lumbar epidural steroid injection (LESI)
• Annaswamy TM, Bierner SM, Chouteau W, Elliott
AC. Muscle Nerve. 2012
• 89 subjects prospectively studied
• Predictor variables regarding response to LESI
• Abnormal EMG is a strong and independent
predictor of a positive response to LESI – long
term pain relief
CONCLUSIONS
• EMG and NCS are excellent diagnostic
tests
• Use solid reference foundation
• Realize limitations
• Don’t overcall