EMG and the Electrodiagnostic Consultation for the Family Physician

Transcription

1 EMG and the Electrodiagnostic Consultation for the Family Physician Stephanie Kopey, D.O., P.T. 9/27/15 The American Association of Neuromuscular & Electrodiagnostic Medicine (AANEM) Marketing Committee has coordinated this presentation as part of an AANEM initiative to increase awareness of electrodiagnostic medicine and the disorders it helps to diagnose. Outline What is an electrodiagnostic consultation? Is an EMG study the same as an electrodiagnostic consultation? Who is qualified to be an electrodiagnostic practitioner? What is the role and value of nerve conduction studies (NCSs) and needle electromyography (EMG)? When should I suspect a neuromuscular disorder? Outline What conditions are commonly evaluated/diagnosed by NCSs/EMG? What are the technical details of these studies? What are some limitations of EMG studies? What can I expect from an EMG report? 1

2 What is an electrodiagnostic consultation? Similar format to a medical consultation Focused neuromusculoskeletal history and physical examination Development of a differential diagnosis Examination of muscles and nerves using nerve conduction studies (NCSs) and needle electromyography (EMG) Formulation of a final diagnosis Is an EMG study the same as an electrodiagnostic consultation? EMG is often used to refer to the entire spectrum of electrodiagnosis of nerve and muscle disease Strictly speaking, an EMG refers to the needle or surface examination of the bioelectrical activity of muscle, which is one component of the electrodiagnostic consultation Who is qualified to be an Electrodiagnostic Practitioner? Physicians trained in electrodiagnostic medicine MD s who have specialized training in the diagnosis and treatment of neuromuscular and neurological diseases, and the application of particular neurophysiologic techniques to the study of these disorders Generally, Neurologists or Physical Medicine and Rehabilitation (PM&R) physicians American Association of Neuromuscular & Electrodiagnostic Medicine Position Statement 2

3 Electrodiagnostic Practitioners NCS may be performed by trained nonphysicians under supervision of electrodiagnostic medicine physicians Needle EMG component should be performed by a electrodiagnostic medicine physician American Association of Neuromuscular & Electrodiagnostic Medicine Position Statement What are the indications for electrodiagnostic consultation/testing? EMG is merely an extension of the physical exam Suspected neuromuscular disease/peripheral nervous system Nerve root pathology Peripheral nerve/plexus pathology Neuromuscular junction pathology Muscle pathology What is the value of NCS/EMG? Confirm the clinical impression of a neuromuscular disorder Rule out certain diagnoses Enhance patient care 3

4 Value of NCSs/EMG When neuromuscular disease is present, electrodiagnostic testing can: Clarify the type of pathology (i.e. neuropathy vs myopathy) Determine severity & extent of pathology Confirm site of pathology Estimate chronicity of pathology Complaints Suggestive of Neuromuscular Pathology Numbness or Tingling Decreased Sensation Pain or Cramping Weakness Gait difficulty Fatigue Disorders Diagnosed/Evaluated by NCS/EMG Generalized Neuropathies Axonal Demyelinating Acquired» Acute; GBS» Chronic; CIDP Hereditary Mixed 4

5 Disorders Diagnosed/Evaluated by NCS/EMG Focal Neuropathies Carpal Tunnel Syndrome (median neuropathy at the wrist) Cubital Tunnel syndrome (ulnar Neuropathy at elbow) Peroneal Nerve Palsy Others: brachial plexus lesions, tarsal tunnel syndrome, etc. Disorders Diagnosed/Evaluated by NCS/EMG Radiculopathy Cervical (C5 through T1) Lumbar (L2 through S1) Motor Neuron Disease Amyotrophic lateral sclerosis (ALS) Spinal muscular atrophy (SMA) Disorders Diagnosed/Evaluated by NCS/EMG Muscle Disease Inflammatory Polymyositis, Dermatomyositis Metabolic Hereditary or Congenital 5

6 Disorders Diagnosed/Evaluated by NCS/EMG Neuromuscular Junction Disease Myasthenia Gravis Lambert Eaton Myasthenic Syndrome Botulism Medication induced Disorders Evaluated/Diagnosed by NCS/EMG Specialized electrodiagnostic expertise can be useful in evaluation of: Ocular muscle weakness Speech difficulties due to weakness of laryngeal muscles Disorders of movement and tone from central nervous system disorders Nerve Conduction Studies (NCS) Technical Information Peripheral nerves are stimulated with an controlled electrical stimulus Responses recorded Compound motor action potential (CMAP) Sensory nerve action potential (SNAP) F wave H- reflex 6

7 Motor NCS Parameters Distal Latency determined by conduction velocity of the nerve, neuromuscular junction & muscle Amplitude determined by number of muscle fibers activated Proximal conduction velocity determined by conduction velocity of the fastest fibers Normal Median Motor Study DL CV Amp (msec) (m/s) (mv) Wrist-APB Elbow-Wrist Sensory NCS Parameters Onset and Peak latencies Conduction velocity determined by velocity of a very few fast fibers Amplitude determined by the number of large sensory fibers activated 7

8 Normal Median Sensory Study 1 msec/div Latency CV Amp (msec) (m/s) (uv) Wrist-D F Waves Useful to assess proximal nerve conduction Helpful in the evaluation of: Radiculopathy Guillian-Barre Syndrome Peripheral neuropathy Other demyelinating neuropathies H Reflexes Useful to assess proximal nerve conduction Helpful in the evaluation of: Polyneuropathy S1 radiculopathy Upper Motor Neuron lesions 8

9 Neuromuscular Junction Testing Repetitive Nerve Stimulation Stimulate nerve with train of supramaximal stimuli before and after exercise Record from muscle Attention to technical factors important More sensitive recording from proximal muscles Repetitive Nerve Stimulation: Normal 3Hz stimulation Repetitive Nerve Stimulation: Myasthenia Gravis 3 Hz stimulation rate 9

10 Technical Details of Needle EMG A needle electrode is placed into the muscle needle is sterile and disposable Muscles examined depends on the clinical question and may be modified depending on NCS findings Detailed knowledge of anatomy is necessary to identify specific locations Needle EMG Muscle is studied at rest and at different levels of sustained, voluntary contraction At rest, the muscle should be silent- any spontaneous activity may signal a nerve or muscle abnormality During activity, the electrical shape and pattern of the response can distinguish between nerve and muscle disease Spontaneous Muscle Electrical Activity Examples: Fibrillation potential/positive waves indicates loss of muscle-nerve connection provides information about the chronicity of the problem Fasciculation spontaneous motor unit potential, may indicate irritability in the motor nerve cell 10

11 Fibrillation Potentials and Positive Sharp Waves Fibrillation Potentials Positive Sharp Waves Fasiculations EMG - Motor Unit Potentials Evaluated during early recruitment Morphologic parameters studied Amplitude Duration Phases 11

12 EMG - Recruitment Recruitment is the pattern of motor unit firing when a muscle contracts Reduced Recruitment - Neuropathy Increased (early) Recruitment - Myopathy Dependent on patient cooperation and effort Normal Recruitment Pattern Specialized Testing Interference pattern analysis Quantitative motor unit analysis Single fiber analysis Segmentation studies Cranial nerve testing Brainstem and somatosensory evoked potentials Pelvic floor and respiratory muscles 12

13 Limitations of NCSs/EMG Generally not helpful in the evaluation/diagnosis of: Pain from joint disease Fibromyalgia or myofascial pain syndromes Central nervous system disorders Disorders that do not arise from the neuromuscular system What to Expect From an EMG Report A clinically and physiologically relevant interpretation/diagnosis An outline of the localization, severity, and acuity of the process Notation of other diagnoses that are detected/excluded Explanation of any technical problems What to Expect From an EMG Report The reason for the referral is addressed Pertinent information that may affect management is provided Need for re-evaluation in the future Urgent need for medical intervention 13

14 What to Expect From an EMG Report Data obtained during the study: (NCS) Amplitude Distal latency Distance Conduction velocity Normal (Reference) data Side-to-side comparison (when appropriate) Limb temperature during the study What to Expect From an EMG Report Data obtained during the study: (EMG) Presence & type of abnormal spontaneous activity Motor unit recruitment Motor unit morphology EMG Pearls Electrodiagnostic studies are a supplement to, and not a replacement, for the history and physical examination Electrodiagnostic results are often timedependent Electrodiagnostic studies are not standardized investigations and may be modified by the practitioner to answer the diagnostic question 14

15 American Association of Neuromuscular & Electrodiagnostic Medicine The AANEM is a nonprofit organization dedicated to the advancement of neuromuscular, musculoskeletal, and electrodiagnostic medicine. For more information about the AANEM and the benefits of membership: Call (507) or Visit 15