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Neuromuscular Junction and Infectious Disorders. Dayna Ryan, PT, DPT Winter 2012. Neuromuscular Junction Diseases. Botulism Myasthenia Gravis Lambert-Eaton Syndrome. Latin: “botulus,” meaning sausage Etiology Neurotoxin produced by Clostridium Botulinum Anaerobic, Gram-positive rods

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neuromuscular junction diseases

Neuromuscular Junction Diseases

Botulism

Myasthenia Gravis

Lambert-Eaton Syndrome

botulism

Latin: “botulus,” meaning sausage

  • Etiology
    • Neurotoxin produced by Clostridium Botulinum
    • Anaerobic, Gram-positive rods
    • Found in improperly preserved or canned foods & contaminated wounds
  • Classification (mode of acquisition)
    • Food-borne (ingested)
    • Wound
    • Unclassified

Botulism

slide4

Lesion

    • Pre-synatic terminals
  • Mechanism
    • Botulinum toxin enters presynaptic terminals
    • Blocks the fusion of ACh vesicles with presynaptic membrane
    • Inhibit ACh release into neuromuscular junction
    • Nerve impulse fails to transmit across the neuromuscular junction
    • Muscle paralysis
  • Progression
    • - Typically get full recovery in both adult & infant
incidence
10 adult & 100 infant cases in US each year

Infant botulism

Age 3 wk - 9 month

Signs and symptoms

Develop within 12-36 hours following ingestion of contaminated food

Mortality rate from 1990 – 1996 in US

Type A (6.7%), type E (6.5%), type B (0%)

Gradual recovery over weeks - 12 months

Incidence
signs symptoms
Signs & Symptoms
  • Develops within 12-36 hours following ingestion of contaminated food
    • Flaccid symmetrical paralysis
    • Blurred & double vision, photophobia
    • Dry mouth,nausea, & vomiting
    • Difficulty in swallowing & speech
    • Respiratory failure can occur in 6-8 hours
treatment
Treatment
  • ABE serumantitoxin (antibodies of type A, B, E toxin)
  • Debridement & antibiotics for wound
  • Removal of toxin from GI (gastric lavage)
  • Supportive measures, e.g. IV, mechanical vent
myasthenia gravis

Myasthenia Gravis

Fluctuating weakness & fatigability

Autoimmune disorder

Abnormal Thymus function in 75% of cases

Classifications of MG

Ocular myasthenia (~10-15%)

Generalized weakness (~85%)

Myasthenic crisis: respiratory failure

mechanism of mg
Mechanism of MG

Antibodies block & damage ACh receptors

  • ACh receptors # reduced; Decreased efficiency of neuromuscular transmission
  • Nerve impulse fails to pass across the neuromuscular junction to cause muscle contraction
myasthenia gravis1
Myasthenia Gravis
  • Prevalence: 14/100,000
  • Ratio of women-to-men= 3:2
  • Factors that exacerbate MG: hyper- or hypothyroidism, menstrual cycle
  • Disease Progression:
    • Slowly, progressive weakness (maximal weakness occurs in first year in 2/3 of all cases)
    • After 15-20 years, weakness becomes fixed
  • Remissions occur in about 25% of cases
signs symptoms1
Signs & Symptoms
  • Generalized weakness: proximal muscles more affected
  • Fatigability of skeletal muscles
    • progressive muscular weakness on exertion, followed by recovery of strength after rest
  • Respiratory impairments
signs symptoms2
Signs & Symptoms
  • Muscle weakness varies day to day and over long periods of time
  • Cranial muscles are the first to show weakness
  • Patients compensate for weak muscles (e.g. use of thumb to close jaw)
diagnosis
Diagnosis
  • Test anti-Ach receptor antibodies
    • if +, then MG
  • Tensilon test
    • Repetitive movements or holding a position
    • Compare performance following giving Tensilon (anticholinesterase) vs. Placebo (saline)
    • If strength/endurance is improved, then MG
  • EMG
    • Reduced amplitudes over repetitive stimulation
slide16

Treatment

    • Anticholinesterase drugs
    • Thymectomy
    • Immunosuppressants
    • Plasmaphoresis
      • Blood is routed to a machine that separates the plasma & cells
      • Plasma, which contains antibodies, dissolved proteins, glucose, clotting factors, etc., is discarded while cells are returned to the body
      • Temporarily (4-6 weeks) reducing anti-ACh receptors antibodies
      • Used to get a patient more stable for surgery or to get them out of crisis
    • Intravenous immunoglobulin (IVIG)
lambert eaton syndrome
Lambert-Eaton Syndrome
  • Rare but still the most frequent presynaptic neuromuscular transmission disorders in adults
  • Etiology
    • ~50% of cases associated with cancer, especially small cell carcinoma of the lung
    • Others primarily from autoimmune disorders
      • e.g. RA, thyroid disease, MS
slide18

Mechanism

    • Antibodies destroy voltage-gated Ca++ channel
    • Block of Ca++ into presynaptic terminal
    • Reduced release of presynaptic ACh vesicles
    • Reduced probability of reaching depolarization threshold of a muscle fiber
signs symptoms3
Signs & Symptoms
  • Muscle weakness and fatigue
    • At proximal limbs & torso (LE > UE)
    • Difficulties climbing stairs, lifting objects
  • Early symptoms: aching of thighs and difficulty walking
  • Decreased or absent DTRs
  • Cranial nerves usually spared
diagnosis1
Diagnosis
  • EMG
    • Will see a low amplitude response to a single stimulation
  • Voltage-gated calcium channel antibody
    • If +, then LEMS
  • MRI or CT scan for lung cancer
infectious disorders of the ns

Infectious Disorders of the NS

Meningitis

Encephalitis

Lyme Disease

West Nile Virus

meningitis
Meningitis

= meninges of the brain and SC become inflamed

    • All 3 layers can be involved, but usually pia and arachnoid
  • Etiology: bacterial or viral infection
    • Viral (Aseptic) – most common
    • Tuberculous – enter by inhalation
    • Bacterial – EMERGENCY!!
  • Incidence: 2-6/1,000,000 adults
signs symptoms4
Signs & Symptoms
  • Fever & chills
  • Severe headache
  • Stiff & painful neck! (cardinal sign)
  • Mental status changes
  • Sensitivity to light (photophobia)
  • Confusion
  • Vomiting
  • Pain in lumbar area and posterior thigh
    • Positive Kernig sign
signs symptoms progression
Signs & Symptoms - Progression
  • Positive Brudzinski sign as it progresses
    • when neck is flexed, patient flexes leg to decreased stretch on meninges
  • Seizures or coma if untreated
  • Focal neurologic signs, e.g. CN palsies or deafness
  • Edema, which causes increased ICP and can lead to lethargy and confusion
bacterial meningitis in a baby
Bacterial Meningitis in a Baby
  • Fever
  • Poor feeding
  • Vomiting
  • Bulging Fontanels
    • Soft spots
  • Seizures
  • High-pitched cry
diagnosis2
Diagnosis
  • Lumbar puncture: CSF analysis & culture
  • Blood culture
  • CT, MRI: brain abscess or infarction
  • Bacterial type
    • Isolation for 3 days
    • Bed rest
    • Antibiotics ASAP
    • Meds for seizure
    • Corticosteroids for cerebral edema or vasculitis
  • Viral type
    • Meds to control headache and nausea
  • Treatment
encephalitis
Encephalitis
  • Lesion Site: gray matter of the CNS
  • Etiology: viral or bacterial infection
  • Most often from viral infection
    • In US, Herpes simplex encephalitis most common; 1/250,000 – 1/500,000
encephalitis1
Encephalitis
  • Most cases: only mild symptoms or asymptomatic
  • Serious cases cause:
    • Fever & chills
    • Headache
    • Nausea & vomiting
    • Mental status changes; irritability
    • Lethargy, fatigue
    • Seizures
    • Stiff neck (if meninges are involved)
    • Bulging fontanels (soft spot in skull) in infants
    • Focal neurological signs, e.g. ataxia, hemiparesis, aphasia
encephalitis2
Encephalitis
  • Prognosis depends on type
    • Mortality rate varies from <1% to 50-70%
    • Permanent neural damage is more likely in infants
  • Diagnose with spinal tap, EEG, CT scan, or MRI
lyme disease

Lyme Disease

Lyme disease was first reported in the US in the town of Old Lyme, Connecticut, in 1975.

Most cases (90%) in mid-Atlantic, northeast, & north central regions.

Lesion Sites:

CNSand PNS

Incidence on the rise

23,763 cases in 2002

slide33

Etiology

    • Bitten by an infected tick carrying the bacterium Borrelia burgdorferi
  • Risk Factors
    • Having a pet
    • Outdoor activities
    • Walking in high grasses
slide34

Signs & Symptoms – Early Stage

    • The initial sign is rash
      • Bull's-eye appearances (i.e. erythema migrans) at the site of tick bite
      • Present in ~80% of patients
      • Gradually expands to ~ 12” across
    • Flu-like symptoms: chills, fever, headache, lethargy, muscle pain
    • Chronic RA is the most commonly recognized symptom
    • Some neurologic and psychiatric symptoms
progression of lyme disease
Progression of Lyme Disease
  • Stage 1
    • Flu-like symptoms and rash (7-14 days after tick bite)
  • Stage 2
    • Generalized fatigue, loss of appetite, vomiting
    • Neurologic or cardiac abnormalities develop weeks to months later
  • Stage 3 (weeks to year later)
    • RA develops in >50% of people who did not receive earlier treatment
      • Affects knees mostly
      • Often unilateral presentation of joint involved
signs symptoms later stages
Signs & Symptoms – Later Stages

Swollen knee from chronic rheumatoid arthritis is most commonly recognized symptom

treatment of lyme disease
Treatment of Lyme Disease
  • Oral antibiotics
  • Removal of tick
  • Joint surgeries

**15% of those who received early treatments still get complications involving heart, joints, and nervous system

MOST people have complete recovery within weeks or months of antibiotic treatment

prevention is key
Prevention is Key
  • Wear long pants
  • Walk on cleared paths
  • Wear high socks and appropriate shoes
  • Wear light-colored clothing to make ticks easier to see
west nile virus

West Nile Virus

It was first discovered in the United States in the summer of 1999 in New York. Since then, the virus has spread throughout the United States

Lesion: CNS, PNS, Multi-systems

(depends on where bitten)

west nile virus1
West Nile Virus

2009 West Nile Virus Activity in US

(Reported to CDC as of December 2009)

west nile virus2
West Nile Virus
  • Etiology:
    • Single-stranded RNA virus from mosquitos primarily
    • Flavivirus
  • No treatment available – only supportive care
  • Risk factors: age, hypertension, diabetes, CAD, immunosuppression
signs symptoms5
Signs & Symptoms
  • ~80% of individuals are asymptomatic
  • ~20% of individuals affected by the virus develop systemic symptoms
    • < 1% develop neurological manifestations
  • Those that do develop nervous system involvement usually evolve a severe illness
    • Mortality rates 12%-14%
presenting signs and symptoms
Presenting Signs and Symptoms
  • Fever
  • Headache
  • Muscle Ache
  • Joint Pain
  • Fatigue
  • Rash (with swollen lymph nodes)
  • Nausea/vomiting
  • Periocular pain
  • Muscle weakness
  • Altered mental status
  • Backache
  • Photophobia
  • GI/Respiratory Symptoms
neurologic signs symptoms
Neurologic Signs & Symptoms
  • Encephalitis
  • Meningitis
  • Meningoencephalitis
  • Anterior myelitis
  • Acute flaccid paralysis
    • Proximal muscles affected more than distal
    • From damage to anterior horn cells
    • Painless, asymmetric weakness
    • No sensory abnormalities
serious signs symptoms
Serious Signs & Symptoms
  • High fever
  • Severe headache
  • Stiff neck
  • Disorientation
  • Coma
  • Tremors
  • Convulsions
  • Muscle weakness
  • Ataxia and extrapyramidal signs
  • CN abnormalities
  • Optic neuritis/vision loss
  • Polyradiculitis
  • Seizures
  • Myelitis
  • Photophobia
  • Numbness
  • Paralysis