Lambert-Eaton Myasthenic Syndrome (LEMS) Quiz

Lambert-Eaton Myasthenic Syndrome (LEMS)

• LEMS is a rare autoimmune disorder that affects the connection between nerve and muscle cells
• Characterized by muscle weakness, fatigue, and autonomic dysfunction
• 80% of cases are associated with small cell lung cancer (SCLC)
• Remaining 20% are non-paraneoplastic, associated with HLA-B8 and HLA-DR3

Pathophysiology

• Autoantibodies against voltage-gated calcium channels (VGCC) in peripheral nerve terminals
• Impaired release of acetylcholine (ACh) from nerve terminals, leading to muscle weakness
• Antibodies against P/Q-type VGCC, reducing ACh release

Clinical Features

• Proximal muscle weakness, especially in the legs
• Autonomic dysfunction: constipation, dry mouth, impotence, and sweating abnormalities
• Ophthalmological symptoms: diplopia, blurred vision
• Respiratory distress, dysarthria, and dysphagia

Diagnosis

• Electrophysiological studies: repeated nerve stimulation, incremental response
• Antibodies against VGCC, P/Q-type VGCC
• Malignancy workup (e.g., chest CT, PET scan)

Treatment

• Treatment of underlying malignancy, if present
• Immunotherapy: IVIG, steroids, and immunosuppressants
• Medications to facilitate ACh release: 3,4-diaminopyridine

Botulism

• Caused by Clostridium botulinum toxin, which cleaves synaptic vesicle proteins
• Toxin types A, B, E, F, and G, each targeting different synaptic proteins
• Blocks neurotransmitter release, leading to muscle weakness and paralysis
• Diagnosis: electromyography, repetitive nerve stimulation, and toxin assay
• Treatment: supportive care, antitoxin administration, and respiratory support### Botulinum Toxin
• Lethal dose for a mouse is 10-12 μg/kg body weight
• Most poisonous toxin

Symptoms of Botulism

• Dry mouth and throat
• Blurry vision
• Difficulty swallowing
• Facial weakness
• Drooping eyelids
• Respiratory paralysis
• Symmetrical descending paralysis of facial, oropharyngeal, limb, and respiratory muscles
• Pupillary paralysis

Treatment

• Antitoxin (equine serum, anaphylaxis, or serum sickness may occur)
• Guanidine hydrochloride
• Neomycin sulfate
• Aminoglycoside antibiotics (e.g., Kanamycin, Gentamicin, Amikacin)
• Polypeptide antibiotics (e.g., Polymyxin B)
• Supportive care in ICU

Diagnosis

• History of exposure
• Identification of botulinum toxin in stool, vomitus, or wound
• Electrodiagnostic tests (e.g., EMG with repetitive stimulation)
• Blood tests for antibody to botulinum toxin
• Plasmapheresis or plasma exchange as a treatment

Other

• LEMS (Lambert-Eaton Myasthenic Syndrome)
• Congenital myasthenic syndrome
• Autoimmune disorder