Introduction to electrodiagnostic testing (EMG/NCS) Calin I. Prodan, MD Department of Neurology University of Oklahoma Health Sciences Center

Electrodiagnostic testing in Neurology Components: Nerve conduction studies (NCS) Needle electromyography (EMG) Other components: Repetitive stimulation Single-fiber EMG Intraoperative monitoring

NCS Sensory nerves: Motor nerves Amplitude Velocity (distance divided by time) Motor nerves Velocity F-wave response Uses a gradually increased amount of electrical stimulation in order to obtain an motor/sensory response

Nerve Conduction Studies Amplitude of the response Amplitude (mV) Time (ms)

Sensory Pathways Receptor organs (sensory transducers) Peripheral nervous system pathway Spinal (ascending) pathway Thalamic “relay” Cortical representation

Pain & Temperature Pathway “Spinothalamic system” Receptors are naked nerve endings Peripheral unmyelinated (C) and small-myelinated (A) fibers Ascending spinal cord pathway Carried to the thalamus The speed of conduction for pain and temperature sensation is very slow

Proprioception Pathway Receptors are specialized organelles including muscle spindles, Golgi tendon organs, and Pacinian corpuscles Peripheral large-myelinated (A and A) fibers Ascending spinal cord pathway Carried to the thalamus The speed of conduction is fast

Spinothalamic vs Proprioception Pathways Pain & temperature Naked nerve endings A and C fibers (slow) PROPRIOCEPTION Proprioception Specialized receptor organelles A and A fibers (fast)

Electrodiagnostic studies: Nerve Conduction Studies 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.

EMG Insertion of a needle electrode in various muscles Recording muscle activity at rest and during activity (volitional activity) Requires a lot of cooperation and cannot be performed accurately in patients with severe weakness

EMG Fibrillation Fasciculations Normal voluntary activity

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

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

When to refer for EMG/NCS Radiculopathy: Part of surgical evaluation for cervical and LS spine surgeries Very low yield in pure sensory c/o or pain Higher yield with weakness and reflex changes Prior to repeating a surgery Post-surgical complications (from the surgical service)

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

Radiculopathy– Electrodiagnostic studies Nerve conduction studies: normal 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

When not to refer for EMG/NCS Radiculopathy: Low back/neck pain with or w/o radicular pattern – patients should be treated medically and imaged (X-ray) Low back/neck pain with sensory c/o or sensory findings -patients should be 1st treated medically and imaged (X-ray) anticoagulation (cannot perform complete EMG) Patient states that he does not want surgery or not a surgical candidate

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

Peripheral Nerve Disease (Neuropathy) Small-Fiber Neuropathy Large-Fiber Neuropathy

Spinothalamic vs Proprioception Pathways Pain & temperature Naked nerve endings A and C fibers (slow) PROPRIOCEPTION Proprioception Specialized receptor organelles A and A fibers (fast)

Length-dependent (dying back) axonal neuropathy

Small-Fiber Neuropathy

Small-Fiber Neuropathy– Electrodiagnostic studies COMPLETELY NORMAL

Large-Fiber Neuropathy History: Constant unsteadiness Frequent falls slow (months/years) progression No numbness, tingling, pain first involves feet/legs then hands/arms

Large-Fiber Neuropathy Examination: 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

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

Electrodiagnostic studies Nerve conduction studies (NCS) the most important non-serologic test for the diagnosis of neuropathy Electromyography (EMG) helps evaluating the effect on muscles rules out muscle disease

Segmental Demyelination Schaumburg, Berger & Thomas, 1992

Demyelinating Polyneuropathies Segmental demyelination is a random process: Statistically more likely to affect longer nerves (i.e. legs) first and most severely. But any nerve segment can be affected, so proximal and facial weakness can occur early. Disruption of large-fiber nerve function: early weakness, areflexia and sensory ataxia. Schaumburg, Berger & Thomas, 1992

Features of Acquired (Segmental) Demyelination: (1) Partial motor conduction block (PMCB) (2) Temporal dispersion (TD) (3) Asymmetric conduction slowing between nerves and in proximal/distal segments of the same nerves

Acquired Demyelinating Polyneuropathies Segmental Demyelination Usually immune mediated ACUTE (nadir within 4 weeks) Guillian-Barré Syndrome Treat with IvIgG or PE CHRONIC (progress slowly for > 6 weeks) CIDP Treat with corticosteroids, IvIgG or PE

When to refer for EMG/NCS Entrapment neuropathy: Part of surgical evaluation (NES, Ortho, plastics) Part of initial evaluation if sensory/motor changes are present After at least 6-8 weeks of smx When not to refer for EMG/NCS: if only sensory c/o (treat – splints, pads, NSAIds, pain management) patient refuses surgery

Focal Neuropathies in the Upper Limb Carpal Tunnel Syndrome (CTS)

Carpal Tunnel Syndrome (CTS) Commonest focal neuropathy encountered Entrapment of the median nerve beneath the flexor retinaculum at the wrist Symptoms: numbness and pain the wrist and hand worse at night and with repetitive motions relieved by shaking Signs: numbness in median nerve distribution weakness/wasting of APB, sparing FDI/ADM Tinel’s and Phalen’s signs

Carpal tunnel syndrome Diagnosis: clinical NCS (80-90% even in mild cases) Labs: always screen for diabetes and thyroid disease NCS: Slow conduction velocity (sensory/motor) across the wrist +/- decreased amplitude +/- prolonged F-wave EMG +/- denervation (acute and/or chronic)

Carpal tunnel syndrome Treatment: wrist splints NSAIDs treat the predisposing condition Surgical release: surgical release (90% success rate) Indicated mostly in moderate and severe cases Outpatient surgery (plastics, ortho, NES, GS)

When to refer for EMG/NCS Myopathy/myositis: Not an early test Serology (including myositis antibodies) and treatment should come first When considering biopsy

Myopathy Werwerwr

Myopathy/Myositis– Electrodiagnostic studies Nerve conduction studies are normal (motor and sensory nerves) EMG - pathy: No denervation (spontaneous activity at rest) Small units when symptomatic muscles are activated even with maximal effort EMG – itis: Denervation

When to refer for EMG/NCS ALS, MG, plexopathy: Not an early test Serology/treatment/imaging should come first

MND

MND

MND– Electrodiagnostic studies Nerve conduction studies: sensory nerves are normal motor nerves +/- low amplitude response conduction velocities are normal EMG: the crucial test for diagnosis widespread denervation changes (spontaneous activities at rest) – fibrillation potentials and fasciculations in all extremities/thorax and even face/tongue

Muscular dystrophy Family history of similar issues Most often EMG/NCS NOT indicated DNA testing available = Myopathy with positive FH

Neuromuscular Junction Disease Post-synaptic NMJ Myasthenia Gravis (MG) Pre-synaptic NMJ Eaton-Lambert syndrome (ELMS)

MG History: Hallmark is fluctuating fatigable weakness. double vision (diplopia) and droopy eyelids – very common (60-70) difficulty swallowing, chewing and talking – common (15-20% limb weakness – less common (10%) weakness fluctuates during the day strength normal in the AM, weakness most pronounced in PM weakness is triggered by repetitive activities strength improves with rest severe cases may lead to respiratory failure and death Hallmark is fluctuating fatigable weakness.

MG – Electrodiagnostic studies Nerve conduction studies are normal (motor and sensory nerves) EMG is normal Repetitive stimulation (2-3 Hz) of a distal motor nerve may produce a decrease in the amplitude of the motor response ( > 10%)

MG – Repetitive stimulation

ELMS History: Heaviness/fatigue in the upper portion of the limbs Trouble going up/down stairs or getting in/out a chair NO double vision/droopy eyelids/difficulty swallowing, chewing or talking Hallmark is improvement with exercise

ELMS – Electrodiagnostic studies Nerve conduction studies are normal (motor and sensory nerves) EMG is normal Repetitive motor stimulation at 2-3 Hz may produce a decrease in the amplitude of the motor response (5- 20%) Repetitive motor stimulation at 20-50 Hz will produce an increase in the amplitude of the motor response (200-500%)

ELMS – Repetitive stimulation

ELMS – Repetitive stimulation

EMG/NCS Involves significant discomfort Relatively expensive ( = MRI) Requires patient cooperation Takes approx. 1 hour

Carpal tunnel screen (CTS) Carpal tunnel screen clinic – EMG lab Screening test: both median nerves across the wrists and both ulnar nerves at the wrist (motor and sensory component) No needle testing Can be done on a same-day basis