82688 peripheral nerve disorders ou

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Peripheral Nerve Disorders

Bill Mulkerin, R1

Key points Peripheral nerve disorders present in up to 10% of population DM most common cause Must exclude CNS and life-threatening causes of weakness first Guillain-Barre requires prompt intervention Acute myasthenic crisis or botulism require close monitoring Most peripheral nerve disorders require formal electrodiagnostic testing

Scope Most disorders benign, but must assess for serious etiologies: Guillain-Barre, myasthenia gravis,

botulismAnatomy Peripheral nervous system = 12 cranial nerves, 31 spinal nerves Injured spinal nerves able to regenerate at rate of 1-3 mm/day Chronic injury (DM + CIDP) can lead to recurrent regeneration and hypertrophy (onion-bulb

formation)

Guillain-BarreAka acute inflammatory dyemyelinating polyneuropathy

Pathophysiology Immune-mediated peripheral nerve myelin sheath destruction Mononuclear inflammatory infiltrate Preceding triggering events: viral or febrile illness, C. jejuni, vaccination Symptoms worst in 2 weeks in 50% of patients, 4 weeks in over 90% of patients Recovery weeks to 1 year Mortality 2-5%

Signs + Symptoms Generally preceded by viral prodrome Ascending symmetrical weakness or paralysis and loss of DTRs

Paralysis may ascend to diaphragm 1/3 of patients will require intubation Findings suggestive of G-B:

o relative symmetryo mild sensory involvemento CN involvemento autonomic dysfunction


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o no fever at onseto cytoalbuminologic dissociation of CSFo typical electrodiagnostic findingso progression over days to weekso recovery beginning 2-4 weeks after cessation of progression

Table 166-2 Diagnostic Criteria for Classic Guillain-Barr Syndrome

Required

Progressive weakness of more than one limb

Areflexia

Suggestive

Progression over days to weeks

Recovery beginning 2

4 wk after cessation of progressionRelative symmetry of symptoms

Mild sensory signs and symptoms

Cranial nerve involvement (Bell's palsy, dysphagia, dysarthria, ophthalmoplegia)

Autonomic dysfunction (tachycardia, bradycardia, dysrhythmias, wide variations in blood pressure, postural hypotension, urinary retention, constipation, facial flushing, anhydrosis,hypersalivation)

Absence of fever at onset

Cytoalbuminologic dissociation of cerebrospinal fluid (high protein and low white cell count)

Typical findings on electromyogram and nerve conduction studies

Variants Classic (AIDP) represents 85-90% of cases in US. Acute Motor Axonal Neuropathy, primarily Mexico, Japan, China, but represents 5-10% of cases in

US Acute Motor + Sensory Axonal Neuropathy mixed motor and sensory, a more severe form of Acute

Motor Axonal Neuropathy Miller-Fisher Syndrome (ophthalmoplegia, ataxia, decreased or absent DTRs, less weakness than

typical GB, milder course; can test for C. jejuni antibody to confirm diagnosis), represents 5% of UScases

Diagnosis Measure vital capacity (VC). Normal 60-70 mL/kg. Count 1-25 in single breath good proxy measure. Indications for intubation: rapid progression, VC < 20 mL/kg, negative inspiratory force (NIF) < -30

cm H2O, decrease of > 30% or either VC or NIF in first 24 hours, autonomic instability


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LP: cytoalbuminologic dissociation, which is high protein with low cell count. Protein > 45 m g/dL,white cell count < 10 cells/mL, predominantly mononuclear cells. If > 100 cells/mL, consider otherdiagnoses (HIV, Lyme disease, syphilis, sarcoidosis, tuberculous or bacterial meningitis, leukemicinfiltration, or CNS vasculitis).

Electrodiagnostic testing: demyelination typical of G-B, variants with motor axonal component mayshow axonal injury pattern, rather than demyelination

MRI to rule out other causes will show enhancement of affected nervesTreatment Assess respiratory status, intubate if indicated:

Table 166-3 Managing Respiratory Failure in Guillain-Barr Syndrome

Indications for intubation

Vital capacity


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Etiology unclear, but thought to be autoimmune Inflammation leads to myelin damage

Signs + Symptoms Progress over weeks to months Weakness > sensory LP shows cytoalbuminologic dissociation, as in G-B Progression more gradual than G-B, respiratory failure rare

Variants Lewis Sumner Syndrome asymmetrical involvement of upper rather than lower extremities Sensory Inflammatory Demyelinating Polyneuropathy distal sensory loss and pain Inflammatory Demyelinating Polyneuropathy in Diabetes rapidly aggressive course, as compated

with diabetic polyneuropathyDiagnosis CSF and nerve biopsy, although controversial

Treatment Corticosteroids equivalent to IVIG and plasmapheresis (diff than GB) Combo therapy no added benefit Antineoplastics can be considered if failure of 1 st line treatment

Diabetic Peripheral NeuropathyPathophysiology Can be distal and symmetric, but also can be mononeuropathy multiplex (50% of DM patients) Most common cause of nontraumatic amputation injury

Signs + Symptoms

Classic: Muscle weakness, atrophy, imbalance, ataxic gait Painful Diabetic Neuropathy: 10% of diabetics, intermittent, worse when attentive and at night,

duration < 6 months Insulin neuritis: small-fiber neuropathy, pain + paresthesias associated with insulin therapy Diabetic Neuropathic Cachexia: weight loss and painful dysethesias of limbs + trunk Hyperglycemic Neuropathy: seen in newly diagnosed diabetics, improves with BG control Asymmetrical Proximal Diabetic Neuropathy: low back, hip, and anterior thigh pain, may be

bilateral.Treatment and Dispo TCAs (amitriptyline, nortriptyline), anticonvulsants (gabapentin, valproate), topical (lido patch,

capsaicin) Diabetes Control and Complications Tria l12 showed a 60% reduction in risk of developing neuropathy

with tight glycemic control Foot care

Isolated Mononeuropathies
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Median Mononeuropathy (Carpal tunnel syndrome)Pathophysiology Compression of median nerve in carpal tunnel Most commonly due to repetitive stress Also caused by DM, amyloidosis, trauma, pregnancy

Signs + symptoms Burning, numbness, pain in median nerve distribution Sensation should be preserved in 5 th and ulnar 4 th digits

Diagnosis Tinels: tapping on palmar aspect of wrist elicits tingling, numbness, or electric shock shooting into

hand Phalens sign: wrists held in flexion for 60 seconds, positive if evokes pai n, numbness, tingling

Treatment Conservative: rest, splinting, weight loss, behavioral modification, avoidance of caffeine, nicotine,

alcohol; consider diuretics if edema plays significant role If conservative fails: corticosteroid injections, then surgical release of flexor retinaculum.

Ulnar Mononeuropathy (Cubital Tunnel Syndrome) 2nd most common compressive mononeuropathy (after carpal tunnel) Tingling in 5 th and lateral 4 th fingers, may progress to numbness and weakness of intrinsic muscles of

hand. Tinels by tapping on cubital tunnel at the elbow Elbow flexed + wrist extended, if signs recur within 3 min, positive Froments sign: thumb intraphalangeal joint flexes to compensate for weakn ess of the adductor

pollicis brevis Guyons Canal Syndrome (Handlebar Palsy): spares sensory fibers and results in intrinsic weakness

only Consider also CN8 entrapment and thoracic outlet syndrome: CN8 entrapment has neck pain +

worsening of symptoms with neck flexion; thoracic outlet syndrome worsens with shoulderabduction

Treatment Pain control (NSAIDS) Rest, reduce repetitive stress, sling, PT/OT

Mononeuropathy MultiplexDysfunction of multiple peripheral nerves separated both temporally and by anatomic locationEtiologies:

Diabetes mellitusVasculitides

Polyartertitis nodosaWegeners granulmatosis


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Temporal arteritisInfectious

Lyme diseaseHIVLeprosyHepatitis

NeoplasmsParaneoplastic syndromeIntraneural neoplastic infiltration

Connective Tissue DisordersSLESjogrens syndrome

Rheumatoid arthritisSarcoidosisLead poisoningPolycythemia veraCryoglobulinemia

Myasthenia GravisPathophysiology Bimodal age of onset: 20-30s, women > men; 50-60s, men > women Auto-antibodies directed against nicotinic acetylcholine receptors (AChRs) at the neuromuscular

junction, causing degradation, dysfunction, and blockade of AChRs 75% of patients with thymic hyperplasia or thymoma With repeated stimulation of same muscle, fewer and fewer binding sites available and fatigue

developsSigns + SymptomsNew Onset Myasthenia Gravis Muscular weakness and fatigability, most often proximal muscles Usually involving ocular (40% at onset, 85% eventually develop) and bulbar muscles at time of ED

presentation Ptosis, diplopia, blurred vision; often worse towards end of day Cogan lid twitch (in which the eyes are lowered for 10 to 20 seconds, then droop or twitch when the

patient attempts to raise them Up to 17% have weakness of muscles of respiration

Acute Myasthenia Crisis

Can be first presentation Respiratory failure requiring intubation 15-20% of patients, usually within first 2 years of disease Underlying infection, aspiration, changes in medications most often trigger VC of 15 mL/kg or less is indication for intubation (less than GB) Can use edrophonium test to differentiate from cholinergic crisis

Congenital Myasthenia Gravis


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12% of pregnant women with MG will give birth to symptomatic infants Symptoms generally disappear after first several days of life Intubation in severe cases, consider exchange transfusion in these patients as well

Lambert Eaton Associated with small-cell carcinoma of lung in 60% of cases Autoantibodies result in inadequate release of acetylcholine from nerve terminals, affecting both

nicotinic and muscarinic receptors With repeated stimulation, ACTH in synaptic cleft increases, leading to increase in strength (opposite

of patients with myasthenia gravis)Diagnosis Serologic testing, edrophonium chloride (AChE inhibitor) test, EMG Receptor-antibody testing positive in 80-90% of patients Ice test is an alternative to edrophonium test

Treatment

Cholinesterase inhibitors: pyridostigmine and neostigmine Immunosuppressant drugs Thymectomy Immunomodulators cyclosporine + cyclophosphamide 31 Avoid depolarizing or non-depolarizing paralytic agents if intubating can use propofol, etomidate,

fentanyl instead

BotulismPathophysiology 2010: 112 cases, 85 of which were infantile Clostridium botulinum, anaerobic spore forming bacterium Toxins A, B, + E (toxin A used in Botox) Wound botulism from heroin skin-popping Toxin type E from preserved or fermented fish and marine mammals Toxin irreversibly binds to presynaptic membrane of peripheral nerves, inhibiting release of ACh, as

new receptors are generated patient improvesSigns + SymptomsClassic Botulism Neither sensory deficit, nor pain Onset 6-48 hours after ingestion Descending, symmetrical paralysis CN and bulbar muscles often affected first: diplopia, dysarthria, and dysphagia. DTRs normal or

diminished. May have anticholinergic symptoms: constipation, urinary retention, dry skin, dry eyes, and

hyperthermia.


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Pupils may be dilated and not reactive. Helpful in distinguishing from MG, which should not affectpupils.

Infantile Botulism 1 week to 11 months, implicated in SIDS. Constipation, poor feeding, lethargy, weak cry. Consider in

DDx of floppy infant

Due to ingestion of spores that germinate and produce toxin at higher pH in infant GI tract. Diagnosis Assay not commonly available. Test food, if possible. Mostly clinical diagnosis and by exclusion of

other possibilities.Treatment

Supportive (intubation). Botulism antitoxin adults

o One vial (10 mL) of trivalent equine antitoxin as soon as diagnosis made.o Skin testing for horse serum sensitivity prior to administration, if possible.

BabyBIG infants IVIG may help decrease mechanical ventilation requirements and length of ICU stay.

References:Adams, Chapter 92

Underwood K, Rubin S, Deakers T, Newth C: Infant botulism: a 30-year experience spanning theintroduction of botulism immune globulin intravenous in the intensive care unit at Childrens HospitalLos Angeles. Pediatrics 120: e1380, 2007.

Andrus P, Jagoda A. Chapter 166. Acute Peripheral Neurologic Lesions. In: Tintinalli JE, Stapczynski JS,Cline DM, Ma OJ, Cydulka RK, Meckler GD, eds. Tintinalli's Emergency Medicine: A Comprehensive StudyGuide . 7th ed. New York: McGraw-Hill; 2011.

Sloan EP, Handel DA, Gaines SA. Chapter 167. Chronic Neurologic Disorders. In: Tintinalli JE, StapczynskiJS, Cline DM, Ma OJ, Cydulka RK, Meckler GD, eds. Tintinalli's Emergency Medicine: A ComprehensiveStudy Guide . 7th ed. New York: McGraw-Hill; 2011.

Lawn ND, Fletcher DD, Henderson RD, et al: Anticipating mechanical ventilation in Guillain-Barr

syndrome. Arch Neurol 58: 893, 2001.

The Diabetes Control and Complications Trial Research Group: The effect of intensive treatment ofdiabetes on the development and progression of long-term complications in insulin-dependent diabetesmellitus. N Engl J Med 329: 977, 1993.


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Hart IK, Sharshar T, Sathasivam S: Immunosuppressant drugs for myasthenia gravis. J Neurol NeurosurgPsychiatry 80(1): 5, 2009.

Drachman DB. Chapter 386. Myasthenia Gravis and Other Diseases of the Neuromuscular Junction. In:Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison's Principles of Internal

Medicine . 18th ed. New York: McGraw-Hill; 2012.

Amato AA, Hauser SL. Chapter 385. Guillain-Barr Syndrome and Other Immune-MediatedNeuropathies. In: Longo DL, Fauci AS, Kasper DL, Hauser SL, Jameson JL, Loscalzo J, eds. Harrison'sPrinciples of Internal Medicine . 18th ed. New York: McGraw-Hill; 2012.

Sztajnkrycer MD, Thurman RJ. Chapter 17. Toxicological Conditions. In: Knoop KJ, Stack LB, Storrow AB,Thurman RJ, eds. The Atlas of Emergency Medicine . 3rd ed. New York: McGraw-Hill; 2010.

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