Updated: 12/31/2016

Lambert-Eaton Syndrome

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Snapshot
  • A 40-year-old man presents with increasing muscle weakness. He reports difficulty rising from seated position and difficulty climbing stairs. He denies any blurry vision or any rashes on his body. He has a 100-pack-year history of smoking. Physical exam reveals proximal muscle weakness, decreased deep tendon reflexes, and dry mucous membranes. A bedside edrophonium test is conducted, which is negative. His chest radiography shows a suspicious finding - the round opacity shown in the square.
Introduction
 

 
  • Progressive weakness caused by autoantibody to presynaptic calcium channel on motor neurons
    • type II hypersensitivity reaction
  • Lambert-Eaton Syndrome (LES) also known as Lambert-Eaton myasthenic syndrome
  • Epidemiology
    • less common than myasthenia gravis
  • Pathogenesis
    • antibodies against presynaptic, voltage-gated Ca2+ channels at neuromuscular junction (see illustration)
    • ↓ acetylcholine (ACh) release
  • Associated conditions
    • small cell (oat cell) carcinoma of lung
      • recall other paraneoplastic secretions may be ACTH or ADH
      • in 40% of patients with LES, cancer is found
    • other autoimmune diseases
  • May be diagnosed with prolonged paralysis following use of neuromuscular blocking agents after surgery
Presentation
  • Symptoms/physical exam
    • proximal muscle weakness
      • difficulty rising from a chair
      • difficulty climbing stairs
    • ↓ tendon reflexes
    • autonomic symptoms
      • dry mouth
      • impotence
    • improves temporarily with muscle use (vs myasthenia gravis, where symptoms worsen with muscle use)
    • spares extraocular muscles
Evaluation
  • Negative edrophonium test
    • cholinesterase inhibitor allows more ACh to present at the neuromuscular junction
    • test is positive if patients regain strength
    • test is negative in LES and positive in myasthenia gravis
  • Voltage-gated Ca2+ channel antibody assay
    • 75-100% of patients
  • ACh receptor antibody assay
    • more commonly positive in myasthenia gravis
    • found occasionally in low titers in LES
Differential Diagnosis
  • Botulism
  • Myasthenia gravis
  • Amyotrophic lateral sclerosis
  • Polymyositis
Treatment
  • Treat underlying malignancy
  • Medical therapy for symptomatic treatment
    • pyridostigmine inhibits acetylcholinesterase
    • 3,4-diaminopyridine (DAP) increases the release of ACh
  • Immunotherapy
    • plasma exchange
    • IVIG
    • oral immunosuppressants azathioprine
Prognosis, Prevention, and Complications
  • Prognosis
    • if with simultaneous malignancy, prognosis is poorer
    • LES does not affect respiratory system as significantly as myasthenia gravis does
  • Complications
    • impaired quality of life
 
 

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Questions (2)
Lab Values
Blood, Plasma, Serum Reference Range
ALT 8-20 U/L
Amylase, serum 25-125 U/L
AST 8-20 U/L
Bilirubin, serum (adult) Total // Direct 0.1-1.0 mg/dL // 0.0-0.3 mg/dL
Calcium, serum (Ca2+) 8.4-10.2 mg/dL
Cholesterol, serum Rec: < 200 mg/dL
Cortisol, serum 0800 h: 5-23 μg/dL //1600 h:
3-15 μg/dL
2000 h: ≤ 50% of 0800 h
Creatine kinase, serum Male: 25-90 U/L
Female: 10-70 U/L
Creatinine, serum 0.6-1.2 mg/dL
Electrolytes, serum  
Sodium (Na+) 136-145 mEq/L
Chloride (Cl-) 95-105 mEq/L
Potassium (K+) 3.5-5.0 mEq/L
Bicarbonate (HCO3-) 22-28 mEq/L
Magnesium (Mg2+) 1.5-2.0 mEq/L
Estriol, total, serum (in pregnancy)  
24-28 wks // 32-36 wks 30-170 ng/mL // 60-280 ng/mL
28-32 wk // 36-40 wks 40-220 ng/mL // 80-350 ng/mL
Ferritin, serum Male: 15-200 ng/mL
Female: 12-150 ng/mL
Follicle-stimulating hormone, serum/plasma Male: 4-25 mIU/mL
Female: premenopause: 4-30 mIU/mL
midcycle peak: 10-90 mIU/mL
postmenopause: 40-250
pH 7.35-7.45
PCO2 33-45 mmHg
PO2 75-105 mmHg
Glucose, serum Fasting: 70-110 mg/dL
2-h postprandial:<120 mg/dL
Growth hormone - arginine stimulation Fasting: <5 ng/mL
Provocative stimuli: > 7ng/mL
Immunoglobulins, serum  
IgA 76-390 mg/dL
IgE 0-380 IU/mL
IgG 650-1500 mg/dL
IgM 40-345 mg/dL
Iron 50-170 μg/dL
Lactate dehydrogenase, serum 45-90 U/L
Luteinizing hormone, serum/plasma Male: 6-23 mIU/mL
Female: follicular phase: 5-30 mIU/mL
midcycle: 75-150 mIU/mL
postmenopause 30-200 mIU/mL
Osmolality, serum 275-295 mOsmol/kd H2O
Parathyroid hormone, serume, N-terminal 230-630 pg/mL
Phosphatase (alkaline), serum (p-NPP at 30° C) 20-70 U/L
Phosphorus (inorganic), serum 3.0-4.5 mg/dL
Prolactin, serum (hPRL) < 20 ng/mL
Proteins, serum  
Total (recumbent) 6.0-7.8 g/dL
Albumin 3.5-5.5 g/dL
Globulin 2.3-3.5 g/dL
Thyroid-stimulating hormone, serum or plasma .5-5.0 μU/mL
Thyroidal iodine (123I) uptake 8%-30% of administered dose/24h
Thyroxine (T4), serum 5-12 μg/dL
Triglycerides, serum 35-160 mg/dL
Triiodothyronine (T3), serum (RIA) 115-190 ng/dL
Triiodothyronine (T3) resin uptake 25%-35%
Urea nitrogen, serum 7-18 mg/dL
Uric acid, serum 3.0-8.2 mg/dL
Hematologic Reference Range
Bleeding time 2-7 minutes
Erythrocyte count Male: 4.3-5.9 million/mm3
Female: 3.5-5.5 million mm3
Erythrocyte sedimentation rate (Westergren) Male: 0-15 mm/h
Female: 0-20 mm/h
Hematocrit Male: 41%-53%
Female: 36%-46%
Hemoglobin A1c ≤ 6 %
Hemoglobin, blood Male: 13.5-17.5 g/dL
Female: 12.0-16.0 g/dL
Hemoglobin, plasma 1-4 mg/dL
Leukocyte count and differential  
Leukocyte count 4,500-11,000/mm3
Segmented neutrophils 54%-62%
Bands 3%-5%
Eosinophils 1%-3%
Basophils 0%-0.75%
Lymphocytes 25%-33%
Monocytes 3%-7%
Mean corpuscular hemoglobin 25.4-34.6 pg/cell
Mean corpuscular hemoglobin concentration 31%-36% Hb/cell
Mean corpuscular volume 80-100 μm3
Partial thromboplastin time (activated) 25-40 seconds
Platelet count 150,000-400,000/mm3
Prothrombin time 11-15 seconds
Reticulocyte count 0.5%-1.5% of red cells
Thrombin time < 2 seconds deviation from control
Volume  
Plasma Male: 25-43 mL/kg
Female: 28-45 mL/kg
Red cell Male: 20-36 mL/kg
Female: 19-31 mL/kg
Cerebrospinal Fluid Reference Range
Cell count 0-5/mm3
Chloride 118-132 mEq/L
Gamma globulin 3%-12% total proteins
Glucose 40-70 mg/dL
Pressure 70-180 mm H2O
Proteins, total < 40 mg/dL
Sweat Reference Range
Chloride 0-35 mmol/L
Urine  
Calcium 100-300 mg/24 h
Chloride Varies with intake
Creatinine clearance Male: 97-137 mL/min
Female: 88-128 mL/min
Estriol, total (in pregnancy)  
30 wks 6-18 mg/24 h
35 wks 9-28 mg/24 h
40 wks 13-42 mg/24 h
17-Hydroxycorticosteroids Male: 3.0-10.0 mg/24 h
Female: 2.0-8.0 mg/24 h
17-Ketosteroids, total Male: 8-20 mg/24 h
Female: 6-15 mg/24 h
Osmolality 50-1400 mOsmol/kg H2O
Oxalate 8-40 μg/mL
Potassium Varies with diet
Proteins, total < 150 mg/24 h
Sodium Varies with diet
Uric acid Varies with diet
Body Mass Index (BMI) Adult: 19-25 kg/m2
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(M1.MK.2) A 65-year-old woman who has smoked 2 packs per day for forty years comes to your practice complaining of a chronic cough, dyspnea, hemoptysis, and difficulty rising from a chair. Based on CXR and biopsy slides shown, you feel that all of the following would be consistent with her diagnosis EXCEPT? Review Topic

QID: 101939
FIGURES:
1

Decreasing muscle strength with repetitive stimulation

32%

(29/91)

2

Blurry vision

10%

(9/91)

3

Antibodies to presynaptic calcium channels

24%

(22/91)

4

Dry mouth

11%

(10/91)

5

Orthostatic hypotension

22%

(20/91)

M1

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