Plexopathies – Electrodiagnostic Approach

Plexopathies – Electrodiagnostic approach

Charles Kassardjian MD MSc FRCPC St. Michael’s Hospital University of Toronto

Disclosures • Advisory board for Akcea, Sanofi Genzyme, Takeda, Alexion, and speaker fees from Sanofi Genzyme and Alexion

Learning Objectives 1. To outline the electrodiagnostic approach to the patient presenting with a possible plexopathy (brachial or lumbosacral) 2. To describe the clinical and electrophysiological findings of brachial and lumbosacral plexopathies 3. Highly recommend: Focal Peripheral Neuropathies by John D. Stewart

1 Definitions • We will only discuss the brachial and lumbosacral plexi today • Peripheral nervous system structures – Complex anatomy – Input from multiple nerve roots – Contribute to major peripheral nerves supplying limbs – “Post-ganglionic” – Not as commonly injured as nerve roots or peripheral nerves

Case 1 • 56M, healthy apart from nasopharyngeal carcinoma diagnosed 5 years earlier and treated with chemotherapy and radiation therapy • 1-2 years after therapy noted restricted neck movements and tightening of the muscles around his neck • 3-4 years after therapy noted sensory symptoms in the medial right hand and forearm, followed by weakness of the right hand and shoulder

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Case 1 • Examination: – CN normal (no Horner’s) – Weakness of R deltoid, biceps, triceps, finger extensors and finger abductors (all around 4/5) – R 1+ biceps, triceps and brachioradialis reflexes – Pinprick impairment over the medial right hand (4th and 5th digits, medial palm) and forearm

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2 Clinical features • History is critical – Temporal course: Acute (post-injury), Subacute (days to weeks), Chronic +/- Progressive – Preceding event or risk factors: Trauma, infection, diabetes, cancer – Presence of pain and relation to other symptoms – Pattern of weakness – Distribution of sensory symptoms

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Differential diagnosis • Cervical or lumbosacral radiculopathy • Cervical myelopathy • Mononeuropathy or multiple mononeuropathies • Motor neuron diseases • MSK (shoulder, hip)

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Why do EDX? • Localize the lesion (plexus, root, nerve) • Identify pattern of involvement (component of plexus, typical “nerves” like AIN or suprascapular) • Severity and timing of lesion • Axonal vs. Demyelinating • Reinnervation and “continuity”: Especially in traumatic plexopathies

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3 Plexopathies – EDX Principles • Plexopathies are POST-ganglionic lesions – If axonal loss à Low amplitudes on motor and sensory NCS – Vs. Radiculopathies where the lesion is preganglionic to dorsal root ganglion à Normal sensory NCS • If pure plexopathy: Needle examination of paraspinal muscles should be normal

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Other investigations • MRI: – Useful to evaluate for: Infiltrative lesions, compression, inflammatory changes or enlargement • Ultrasound (more for brachial): – Able to image multiple components of the plexus – Can be done at the time of EDX • X-ray of C-spine: – Screen for cervical rib or elongated C7 transverse process • Blood work: – Screening for inflammatory, metabolic, systemic disease

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Anatomy – Brachial plexus

Aids to the Examination of the PNS, 2000

4 Anatomy – Brachial plexus • “Supraclavicular plexus” • Nerve roots + Trunks • Upper, Middle and Lower trunks • More common than “infraclavicular” • Etiological differences

Aids to the Examination of the PNS, 2000

Anatomy – Brachial plexus • “Retroclavicular plexus” • Divisions • Anterior and posterior divisions

Aids to the Examination of the PNS, 2000

Anatomy – Brachial plexus • “Infraclavicular plexus” • Cords and proximal components of peripheral nerves • Lateral, Posterior, and Medial cords

Aids to the Examination of the PNS, 2000

5 Brachial plexopathies - NCS

Study Component evaluated Median motor - APB Lower trunk, Medial cord Ulnar motor – ADM, FDI Lower trunk, Medial cord Radial motor – EDC, EIP Middle trunk/Lower trunk, Posterior cord Median sensory – D2 Upper trunk, Lateral cord Ulnar sensory – D5 Lower trunk, Medial cord Radial sensory Upper trunk, Posterior cord Lateral antebrachial cutaneous Upper trunk, Lateral cord Medial antebrachial cutaneous Lower trunk, Medial cord

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Brachial plexopathies - NCS

Rubin, 2020

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Brachial plexopathies – NCS • Most are axonal lesions: – Expect low amplitude responses (CMAP, SNAP) in distribution of lesion – Relative sparing of conduction velocity, latencies

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6 Brachial plexopathies – Needle Exam • Sparing of paraspinals in pure plexopathy • Etiologic clue: Myokymic discharges in radiation plexopathy • Reduced recruitment • Fibrillation potentials/PSWs • Large motor unit potentials • Early re-innervation and “nascent” MUPs

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Brachial plexopathies – Etiologies Inflammatory Parsonage-Turner syndrome Diabetic cervical radiculoplexus neuropathy Multifocal forms of CIDP Infectious VZV radiculoplexopathy Traumatic Penetrating Non-penetrating Birth (e.g. Erbs or Dejerine-Klumpke palsies) Burners and Stingers Neoplastic Primary neural tumours Metastatic invasion Radiation Genetic Hereditary neuralgic amyotrophy (SEPT9) HNPP Compressive True neurogenic thoracic outlet syndrome Post-sternotomy

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7 Case 1 • Examination: – CN normal (no Horner’s) – Weakness of R deltoid, biceps, triceps, finger extensors and finger abductors (all around 4/5) – 1+ biceps, triceps and brachioradialis reflexes – Pinprick impairment over the medial right hand and forearm

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NCS Motor Nerve Amplitude CV (m/s) DL (ms) R Median 4.2 53 3.9 R Ulnar 3.5 51 2.7 Sensory Nerve R Median 5 3.5 L Median 18 3.1 R Ulnar 5 3.1 L Ulnar 17 2.5 R Radial 6 2.3 L Radial 24 2.3 R MABC 3 2.7 L MABC 8 2.6 R LABC 3 2.8 L LABC 5 2.5 1/26/21 23

Needle exam

• Fasciculation potentials and large MUPs in the biceps, deltoid, FDI and FPL

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8 Other investigations and diagnosis • MRI of the cervical spine and right brachial plexus: Unremarkable

• Diagnosis: Radiation-induced right brachial plexopathy

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Radiation plexopathy • Radiation often for breast, head, neck or lung ca • RF: Dose of radiation • Any part of the plexus can be involved • Present with paresthesias, numbness, weakness and atrophy, slowing progressing • Variable delay from radiation: Months to many years

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Evaluation • EMG: – Myokymic discharges more common in radiation plexopathy vs. neoplastic (about 60% of patients) (Harper et al. 1989) • Imaging: – Often performed to rule out neoplastic invasion – May see T2 hyperintensity, but often normal • Treatment: – Supportive – Either slow decline or stabilization in most patients

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9 Case 2 • 74M presents with 6 weeks of burning and stabbing pain in the right arm, radiating from the shoulder – Weakness of the right arm subsequently developed about a week later, including wrist and finger drop • 2 weeks prior to neurological symptoms, developed a vesicular rash on the dorsum of the right arm and forearm

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Case 2 Motor Nerve Amplitude CV (m/s) DL (ms) R Median 6.9 51 3.9 R Ulnar 3.8 51 3.1 Sensory Nerve R Median 9 3.5 L Median 12 3.3 R Ulnar NR -- L Ulnar 9 3.0 R Radial NR --

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Case 2

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10 Case 2 • Swab of vesicle positive for VZV (was already treated with acyclovir for presumed shingles zoster) • Over next 2 months, patient’s symptoms improved (pain, sensory), and strength gradually improved (not to baseline)

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Case 2

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Zoster associated limb paresis • Large series (49 patients) with vesicular eruption + weakness of same limb within 30 days of rash (Jones et al. 2014) • Mean age 71, 67% were men • Most had prolonged weakness (~200 d) and few had complete resolution

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11 Zoster associated limb paresis

Jones et al, 2014

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Zoster associated limb paresis

Jones et al, 2014

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Zoster associated limb paresis • MRI: About 25-60% of the time may show nerve enlargement or T2 hyperintensity (no enhancement)

Zubair et al. 2017

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12 Neuralgic amyotrophy • Immune-mediated process • Not really a “plexopathy” as much as multiple neuropathies • Associations: Viral infections, vaccines, trauma, pregnancy, surgery, exercise

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Neuralgic amyotrophy • Acute-subacute onset of arm and shoulder pain • Weakness: Usually days to weeks later, as pain subsiding • Any part of the plexus, but often weakness in distribution of specific nerves – Arising from plexus: Suprascapular nerve, axillary, AIN – Or not arising from plexus: LTN, phrenic • Can be bilateral in 20-30%

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Neuralgic amyotrophy

Ferrante and Wilbourn, 2017

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13 Imaging in Neuralgic amyotrophy • MRI may show T2 hyperintensities – Either in specific portions of the plexus – Or in individual nerves distal to plexus – Or in specific fascicles destined to be nerve branches (e.g. AIN, Pham et al. 2014)

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Imaging in Neuralgic amyotrophy • Hour-glass constrictions of nerve – May correlate with persisting deficits – Indication for surgical exploration and neurolysis?

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Neuralgic amyotrophy • Varied descriptions of prognosis: Most generally favorable (improvement between 1-3 years), while recent studies suggest many have persisting deficit at 3 years • No evidence-based treatment (? Steroids) • Pain management, physical therapy

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14 Case 3 • 63F presents with left leg pain and weakness – 2 months earlier developed left leg and hip pain, along with burning and tingling over the left thigh – Within a week, noted left leg giving out and falls, followed by left foot drop • PMH: DM2 (well controlled) • Her examination demonstrated – 3/5 weakness for left quadriceps and foot DF – 4/5 weakness of hamstrings and plantarflexion – Absent left ankle and knee jerks – Reduced pinprick over the left thigh and dorsal foot

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NCS Motor Nerve Amplitude CV (m/s) DL (ms) L Peroneal NR -- -- R Peroneal 2.8 41 5.6 L Tibial 1.5 39 5.8 R Tibial 8 42 5.7 Sensory Nerve L Sural NR -- R Sural 6 4.2 L Superficial peroneal NR -- R Superficial peroneal 3 3.2

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Case 3 • Needle examination: – Fibrillation potentials + PSWs: Vastus medialis, adductor longus, tibialis anterior, TFL – Paraspinals normal

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15 Case 3 • MRI of the LS spine and plexus: Unremarkable

• CSF and nerve biopsy deferred

• Diagnosis: Diabetic LS Radiculoplexus neuropathy

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Anatomy – Lumbosacral plexus

Aids to the Examination of the PNS, 2000

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Lumbosacral plexopathies - NCS

Study Component evaluated Peroneal motor – EDB, TA LS trunk, sacral plexus Tibial motor – AH Sacral plexus Femoral motor – Quadriceps* Lumbar plexus Sural sensory Sacral plexus Superficial peroneal sensory LS trunk, sacral plexus Medial and lateral plantars Sacral plexus Saphenous sensory* Lumbar plexus Lateral cutaneous nerve of thigh* Lumbar plexus

Note: More technical issues, especially with age and comorbid conditions, may need side to side comparisons

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16 LS plexopathies – Needle Exam • Sparing of paraspinals in pure plexopathy • May help establish “myotomal” nature rather than single peripheral nerves • Lumbar plexus: Iliopsoas, vastus muscles, adductor longus • Sacral plexus: Hamstrings, tibialis anterior, peroneus longus, medial gastrocnemius, tibialis posterior • Superior gluteal nerve: TFL, gluteus medius • Inferior gluteal nerve: Gluteus maximus

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LS plexopathies – Etiologies

Inflammatory Diabetic and non-diabetic lumbosacral radiculoplexus neuropathy Multifocal forms of CIDP MMN Infectious VZV radiculoplexopathy Traumatic / Iatrogenic Penetrating or Non-penetrating Childbirth Surgical or positioning Neoplastic Primary neural tumours or Metastatic invasion Radiation Compressive Hematoma

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Diabetic LSRPN • Similar syndrome occurs in non-diabetics • Share similar clinical features • Acute to subacute pain in the leg (thigh, leg, buttock, even back) • Followed by weakness and atrophy • May affect both legs usually sequentially (usually by 3 months) • Weight loss common precedes neurological symptoms

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17 Diabetic LSRPN • NCS: Findings of axonal loss, often patchy • EMG: Needle examination may show paraspinal muscle abnormalities (radiculoplexus) • Nerve biopsies: – Findings of ischemia: Focal or multifocal fiber degeneration, epineural neovascularization – Epineural inflammatory collections + Microvasculitis

Dyck et al, 2001

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Diabetic LSRPN • Monophasic in most (~80%) • But can be severe causing disability with incomplete recovery • No approved therapy but corticosteroids can be used in some cases (improves pain, unclear impact on neurological deficit)

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Summary • Brachial and LS plexopathies can be hard to distinguish from radiculopathies or mononeuropathies • History is crucial, looking for risk factors or typical syndrome • Electrodiagnosis can help localize (pre-ganglionic vs. post-ganglionic)

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18 Thank you!

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