EMG II Academic half-day 2008 Dr. Fraser Moore [email protected]

QUESTIONS FROM LAST TIME ?

NCS BOTTOM-LINE Axon loss Demyelination Conduction block Amplitude Latency Conduction velocity Neuropathy Localization Motor/sensory Axonal Demyelinating

PLAN TODAY IV.

Needle EMG NEXT TIME V. Late responses VI. Neuromuscular Junction

IV. NEEDLE EMG

1.

2.

3.

4.

5.

6.

Insertional activity Activity at rest Motor unit potentials Disorders Limitations Report

WHY DO WE DO THE NEEDLE EXAM ?

• Help to localize • Identify chronicity and prognosis • Distinguish between neuropathy and myopathy

NEEDLE EXAM • Observe electrical activity of muscle: – With needle mvmt – At rest – With vol. activation • Motor unit potentials

1. INSERTIONAL ACTIVITY • Discharges of muscle fibers irritated by passage of needle • Increased with increased irritability of muscle fibers

2. ACTIVITY AT REST • Fibrillations and positive sharp waves • Spontaneous firing of individual muscle fibers (muscle fiber action potentials)

3. MOTOR UNIT POTENTIALS • Summation of all muscle fiber action potentials of one motor unit • Amplitude depends on nearby fibers • Duration depends on all fibers • Phases depend on timing therefore…* Will change with change in needle position.

(Note: MUP = MUAP)

MOTOR UNIT POTENTIALS

MOTOR UNIT POTENTIALS • Amplitude • Duration • Phases • Stability • Recruitment

RECRUITMENT

4. DISORDERS

Axonal injury: a dynamic process !

• Loss MUAP’s = decreased recruitment • Denervation = fibrillations

4. DISORDERS

Axonal injury: a dynamic process !

• Loss MUAP’s = decreased recruitment • Denervation = fibrillations • Initial reinnervation = long, polyphasic • Maturation = large

MOTOR UNIT POTENTIALS • Amplitude • Duration • Phases • Stability • Recruitment

4. DISORDERS cont… Myopathy = loss of muscle fibers, so MUAPs are: – Smaller amplitude, shorter duration – Polyphasic – Fast recruitment but…* Inflammation = fibrillation Hypertrophy = Larger amplitude

MOTOR UNIT POTENTIALS • Amplitude • Duration • Phases • Stability • Recruitment

COMPARISON Fibrillations MUP Amplitude MUP Duration Polyphasic But…

Recruitment

Neuropathy present increased long yes “neurogenic” “dynamic”

decreased

Myopathy absent decreased short yes “myogenic” exceptions

increased

5. LIMITATIONS • Choice of muscles • Time spent on each muscle • Needle position A subjective test !

6. NEEDLE EXAM REPORT* Muscle 1 Muscle 2 Insertional Fibrillations Ampl. Dur. Recruitment Notes   + N ++ N     poly v. poly Muscle 3 N Muscle 4 N Muscle 5 N 0 N N N 0 N N N 0 N N N (Note: the report will usually concentrate on abnormal motor units. For example, muscles 1 and 2 could also have many normal motor units)

NEEDLE EXAM BOTTOM LINE MFAP MUAP CMAP Localize Chronicity/Prognosis Neuropathy vs.

Myopathy

CASES (Part I and Part II)

1. CARPAL TUNNEL SYNDROME • Technique: -median and ulnar conductions -motor and sensory • Pathophysiology: -compression -demyelination -axon loss From JAMA 2000;283:3110

TYPICAL FINDINGS

THREE QUESTIONS 1.

Does the needle exam help ?

2.

How can we get more “precise” and sensitive?

3.

Any other ways?

2. ULNAR NEUROPATHY AT THE ELBOW • Pathophysiology: -compression, demyelination, axon loss • Look for focal slowing across elbow • If axonal, may not be able to localize*

ELBOW WRIST

LIMITATIONS OF NEEDLE EXAM • May be demyelinating • Can see fascicular involvement • No ulnar muscles above elbow • 2 sites of ulnar involvement at the elbow*

3. MYOPATHY • Normal or diminished CMAP • Fibrillations if inflammatory • Small, short, polyphasic MUAPs • Large MUAP’s if hypertrophy •

Increased recruitment

MYOPATHY cont… “Rule out myopathy” doesn’t work well: -patchy involvement of muscle fibers, we look at motor units -can see increased amplitude, can see fibs -recruitment difficult to judge

UNUSUAL FINDINGS • Complex repetitive discharge • Sudden start and stop, fixed morphology, MFAPs • Myotonic discharge • Wax and wane, MFAPs • Myokymic discharge • Rhythmic firing of single MUAP • Neuromyotonic discharge • Non-rhythmic, extremely rapid firing of single MUAP

NCS BOTTOM-LINE Axon loss Demyelination Conduction block Amplitude Latency Conduction velocity Neuropathy Localization Motor/sensory Axonal Demyelinating

NEEDLE EXAM BOTTOM LINE MFAP MUAP CMAP Localize Chronicity/Prognosis Neuropathy vs.

Myopathy

REMEMBER… History, NE, NCS, needle exam interpreted together (if something doesn’t fit, start over)

TAKE HOME MESSAGE • Ask a specific question when you order an EMG • Interpret the report • Was the appropriate testing done?

• Are the conclusions appropriate for the results ?

• Think beyond positive or negative • Think anatomy and pathophysiology

QUESTIONS

REFERENCES • Aids to the examination of the peripheral nervous system. • ISBN 0-7020-2512-7 • Good overview

REFERENCES • Stewart J.

• Focal Peripheral Neuropathies • ISBN 0-7817-1717-5 • Much better for nerves

REFERENCES • Katirji B. • Electromyography in clinical practice. A case study approach. • ISBN 0-8151-4971-9

REFERENCES • Preston and Shapiro.

• Electromyography and Neuromuscular Disorders. Clinical electrophysiological correlations.

• ISBN 0-7506-7492-X

REFERENCES AAEM Minimonographs (Muscle+Nerve) Glossary of terms (Oct 1987) Waveforms (Oct 1987) Motor unit recruitment (1991;14:489) Nerve Injury (2000;23:863) Radiculopathy (1988;11:1099) (and others…)

REFERENCES Chalk CH. Acquired peripheral neuropathy. Neurol Clinics 1997; 15: 501.

Practice parameter for electrodiagnostic studies in carpal tunnel syndrome. Muscle and Nerve 2002;25:918.

Stewart JD. The variable clinical manifestations of ulnar neuropathies at the elbow. JNNP 1987; 50: 252.

Campbell WW. Evaluation and management of peripheral nerve injury. Clin Neurophysiol 2008; 119: 1951.

REFERENCES Kimura Electrodiagnosis in diseases of nerve and muscle Dumitru Electrodiagnostic medicine ISBN 978-1560534334 ISBN 978-0195129779 Use these as references if you have specific (technical) questions