EMG AND NCS: A PRACTICAL APPROACH TO ELECTRODIAGNOSTICS

Transcription

1 EMG AND NCS: A PRACTICAL APPROACH TO ELECTRODIAGNOSTICS Dr. Harp Sangha, Dr. Tania R. Bruno Staff Physiatrists Toronto Rehab UHN Lecturers, Department of Medicine University of Toronto February 1, 2013

2 Objectives At the end of this session, participants should: Be able to identify the basic nerve conduction studies (NCS) and needle EMG tests used to assess peripheral nervous system dysfunction Determine the types of clinical questions that can be answered by way of NCS/EMG

3 Outline Introduction Overview of the principles of electrodiagnostic testing Review of relevant anatomy and pathophysiology Nerve conduction studies and EMG simplified through relevant cases typically seen in a sports medicine clinic

4 Introduction Diagnostic imaging is to structure what electrodiagnostic tests are to function Diagnostic imaging and electrodiagnostic findings are complementary and one does not replace the other By capitalizing on our understanding of electrical signals throughout the body, we can capture and record biological responses previously hidden to our view

5 Anatomy/Physiology

6 Anatomy/Physiology

7 Anatomy/Physiology

8 Anatomy/Physiology

9 Anatomy/Physiology

10 Anatomy/Physiology What do we mean by the Peripheral Nervous System (PNS)? Motor neuron (anterior horn cells) Sensory neuron (dorsal root ganglion) Nerve root Plexus (brachial, lumbar and lumbo-sacral) Peripheral Nerve Neuromuscular Junction Muscle NB PNS includes CN III-XII

11 Anatomy/Physiology

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13 Nerve Damage and Repair WALLERIAN DEGENERATION The time course is very predictable: WALLERIAN DEGENERATION completes in 7 days for motor nerves completes in 11 days for sensory nerves

14 Nerve Damage and Repair DYING BACK Remember: Distal parts of the neuron are vulnerable due to their distance from the cell body (metabolic power house for the entire structure) This mechanism is operant in many polyneuropathies AXONAL DEGENERATION

15 Nerve Damage and Repair SEGMENTAL DEMYELINATION Demyelination: Leaves the underlying axon intact SEGMENTAL DEMYELINATION Membrane function obviously changes and the ability to conduct electrical impulses declines Myelin regeneration is possible but never repairs as well as the original Typically thinner and shorter in terms of axonal coverage

16 NCS/EMG As an extension of the history and physical exam, Electrodiagnosis (Nerve Conduction Studies and Electromyography) can be invaluable in identifying the type, severity and location of nerve injury post-operatively

17 NCS/EMG

18 Electrodiagnostic testing Two Main Components: Nerve conduction studies (NCS) Needle electromyography (EMG)

19 NCS Test both Motor and Sensory Measure: Amplitude Velocity (distance divided by time) Uses a gradually increased amount of electrical stimulation in order to obtain an motor/sensory response

20 Spinothalamic vs Proprioception Pathways SPINOTHALAMIC Pain & temperature Naked nerve endings A and C fibers (small, slow) PROPRIOCEPTION Proprioception Specialized receptor organelles A and A fibers (large, fast)

21 NCS will only study large-myelinated nerve fibers, distal to the DRG. Hence, they are normal in myelopathy, radiculopathy and small-fiber neuropathy, despite clinically evident sensory loss. Electrodiagnostic studies: Nerve Conduction Studies

22 NCS Waveform Parameters: Distal latency Amplitude Conduction Velocity Area

23 NCS Standard Nerve Conduction Studies: Upper and lower limb motor studies (median, ulnar, radial and tibial and peroneal) Less commonly, musculocutaneous and axillary studies Upper and lower limb antidromic or orthodromic sensory studies (median, ulnar, radial, sural and superficial peroneal) Less commonly lateral and medial antebrachial, lateral femoral cutaneous and saphenous Late responses: F waves and H-reflex Upper and lower limb mixed nerve studies (transpalmar and medial/lateral plantar studies)

24 Motor studies: The time for the electrical signal to cross the neuromuscular junction in the form of neurotransmitter release, activate the muscle action potentials and impulse to travel to the surface recording electrode is an unknown Two point studies or more are, therefore, essential NCS

25 STANDARD STUDIES SNAP Sensory studies: Distal latencies tend to be much faster than in motor studies They are highly susceptible to distortion by shock artefact and noise

26 NCS

27 NCS/EMG

28 EMG

29 EMG Insertion of a needle electrode in various muscles Recording muscle activity at rest and during activity (volitional activity)

30 EMG Fibrillation Fasciculations Normal voluntary activity

31 Electromyography Insertional Activity: electrical signals generated by mechanically deforming the muscle fiber membrane; response varies depending on whether there is or is not proper nervous input to the muscle membrane Spontaneous Activity: abnormal electrical discharges generated depending on state of nervous input and health of the muscle

32 Electromyography Motor Unit Action Potentials: waveforms of summated action potentials from all fibers innervated by the same alpha motor neuron (stability, morphology, firing rate assessed) Recruitment: organized pattern of voluntary muscle fiber firing generated in relation to the contractile force output required Interference pattern: recording of all possible motor unit action potentials at maximum effort

33 Example: Spontaneous Activity Positive Sharp Waves Fibrillation Potentials

34 EMG/NCS Indications: Entrapment neuropathy (carpal tunnel, ulnar neuropathy, etc.) Radiculopathy Polyneuropathy Plexopathy Myopathy/Myositis ALS Myasthenia gravis Any combination of the above

35 Focal Neuropathies Carpal Tunnel Syndrome (CTS)

36 Motor study mv Sensory study

37 CTS Normal Motor = onset latency < 4.2ms, amp >5.0mV Normal Sensory = peak latency < 3.7ms, amp >20µV Conduction Velocities in upper extremities generally >50m/s

38 Radiculopathy EDx in Radiculopathy: Confirms diagnosis and suggests severity Determines: level, acute versus chronic process Serial studies can monitor improvement versus deterioration Part of interventional (epidural) or surgical planning Very low yield in pure sensory c/o or pain Higher yield with weakness and reflex changes

39 Radiculopathies Numbness and pain in the appropriate dermatomal distribution. Often associated with focal myotomal weakness, focal hyporeflexia and back pain.

40 Radiculopathy Electrodiagnostic studies Nerve conduction studies: generally normal (unless severe) EMG: denervation changes (fibrillation potentials and fasciculations) within muscles innervated by the root involved and paraspinal muscles adjacent to the root other muscles in the same extremity and any other muscles are normal

41 Needle EMG in Radiculopathy Acute/Subacute changes: Fibrillations, Positive sharp waves (i.e. spontaneous activity) Suggests active process more likely to require work-up and more involved management Chronic Motor Unit Changes Normal Polyphasic large amplitude If no new denervation, after 4-6 months, unable to determine how longstanding such changes are

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43 Acute (spontaneous activity) - weeks Chronic (Motor Unit Analysis) months-years Polyphasic Large amplitude

44 What Level? EMG shows: -denervation changes (fibrillation potentials and PSWs) within muscles innervated by the root involved and paraspinal muscles adjacent to the root -other muscles in the same extremity and any other muscles are normal

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48 Radiculopathy When not to refer: Low back/neck pain w/o radicular pattern patients should be treated medically and imaged as appropriate...

49 Live Demonstration

50 Case I 45 year old female Nocturnal parathsesias to left hand 1 year ago Has progressed to bilateral symptoms - constant to left, and intermittent to right

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53 Case I What is the diagnosis? Is it purely demyelinating?

54 Case II 64 year old gentleman presents with footdrop Complaints of numbness over the dorsum of the foot Examination Ankle DF, Everters, and Toe extensors 2/5, all other muscles 5/5 Sensory loss over dorsum of foot

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57 Case II Provide a differential diagnosis What diagnosis does the EDx suggest?

58 When to refer for EMG/NCS Polyneuropathy: Consider risk factors (including DM and ETOH) Not an early test Serology should come first

59 Peripheral Nerve Disease (Neuropathy) Large-Fiber Neuropathy diabetes, ETOH, drug induced (taxol, cis-platinum), Vit B12 deficiency, autoimmune, infection, hereditary, idiopathic Small-Fiber Neuropathy (normal NCS*) diabetes, connective tissue diseases, sarcoidosis, hypothyroidism, vitamin B12 deficiency, paraproteinemia, hiv, celiac disease, paraneoplastic syndrome, idiopathic

60 Small-Fiber Neuropathy Electrodiagnostic studies COMPLETELY NORMAL

61 Large-Fiber Neuropathy History: Constant unsteadiness Frequent falls slow (months/years) progression numbness, tingling, pain are less salient feature first involves feet/legs then hands/arms

62 Examination: Large-Fiber Neuropathy Decreased proprioception (joint position) and vibratory sense (tuning fork) in a stocking and glove distribution Normal OR decreased temperature/pain sensation in a stocking and glove distribution Reflexes are decreased (legs > arms) Gait is very unsteady (wide-based) Weakness in feet > hands is a late sign

63 Large-Fiber Neuropathy Electrodiagnostic studies Nerve conduction studies: decreased amplitude or absent responses changes are greater in the lower extremities than upper extremities EMG: normal in longstanding disease it may show denervation in distal muscles

64 Polyneuropathy EDx Studies Nerve conduction studies (NCS) the most important non-serologic test for the diagnosis of neuropathy Electromyography (EMG) helps evaluate the effect on muscles rules out muscle disease

65 Myopathy Electrodiagnostic studies Nerve conduction studies usually normal (motor and sensory nerves) EMG - Spontaneous activity at rest (fibrillations, PSW) Small units when symptomatic muscles are activated even with maximal effort

66 When else to refer for EMG/NCS?ALS,?MG,?plexopathy: Much less common Therefore, discussion of EDx findings out of scope of this talk Serology/consultation/imaging/treatment should occur in parallel with EMG/NCS

67 Why EMG/NCS by Physiatry? Often in primary care setting, presentation is not clearly MSK or neurological Eg.?True radiculopathy vs?msk entity with referred symptoms Management Medications, F/U, physio, bracing, injections/epidurals, surgical referrals, investigations/tx of MSK entities

68 EMG/NCS Extension of clinical diagnosis NOT to make a dx Grade severity (mild, moderate, severe) i.e. define the need for medical or surgical intervention Exclude other diagnosis Prognosis (myasthenia, ALS, GBS)

69 Conclusion Integrity of the motor and sensory nerves can be ascertained directly from NCS Direct information regarding health of muscle and the neuromuscular junction and indirect information regarding state of muscular innervation is provided by EMG Knowing the root level, plexus and terminal branch innervation of each sampled muscle can help localize the site of nerve lesion and provide information regarding the acuity or chronicity of that lesion

70 Conclusion If appropriately timed (i.e. not too early postinjury), NCS and EMG can be an invaluable tool Identification/confirmation of injury or pathology; prognostication of recovery/degree of likely residual deficits; localization of lesion site can lead to appropriate treatment, be it compensatory or restorative