Lambert-Eaton Myasthenic Syndrome

Lambert-Eaton myasthenic syndrome (LEMS) is an autoimmune disease, often paraneoplastic, in which antibodies develop to the presynaptic acetylcholine-releasing terminal of the neuromuscular junction and parasympathetic effector junction resulting in decreased acetylcholine release. Age of onset is 40 to 80 years old.

Causes

Lambert-Eaton myasthenic syndrome is an uncommon neuromuscular disorder such as includes:

• Weakness in muscles of the upper arms and upper legs and less commonly.
• Muscles of the neck.
• Speech.
• Swallowing.
• Breathing and eye movement.

Lambert-Eaton myasthenic syndrome is an autoimmune disease, referring to the fact that antibodies are produced by the body against its own tissues. The disorder is not hereditary. Lambert-Eaton myasthenic syndrome is associated in fourty percent of cases with cancer, most often with small cell cancer of the lung and less often with other tumors. The neuromuscular defect in Lambert-Eaton myasthenic syndrome is due to insufficient release of the neurotransmitter acetylcholine by nerve cells.

Symptoms

• Presents insidiously as proximal muscle weakness, especially the thighs and hips, and autonomic dysfunction
• Ptosis has been reported in up to 25% of patients.
• Autonomic dysfunction includes dry mouth, impotence, and
  postural hypotension.
• Respiratory weakness may be seen but is generally neither common nor severe. Prolonged paralysis may develop in some patients postoperatively with the use of neuromuscular blocking agents.

Signs

• Proximal muscle weakness
• Hyporeflexia, which follows the weakness
• Waddling gait due to hip weakness
• Sensation and sensorium are normal.
• Dry mouth, postural hypotension, and ptosis may be found.

Treatment

The goal of treatment is to identify and treat any tumors. Plasmapheresis, where blood plasma is removed and replaced with fluid, may improve symptoms.

Prednisone or other medications that suppress the immune response may improve symptoms in some cases. Medications can also include anticholinesterase medications such as Neostigmine or Pyridostigmine.