Lambert-Eaton syndrome is characterized by muscle weakness that improves with continued contraction of the muscle .
Causes, incidence, and risk factors
Lambert-Eaton syndrome (myasthenic syndrome) is a disorder with symptoms very similar to those of myasthenia gravis . There is muscle weakness associated with disturbed communication between nerves and muscles. In myasthenia gravis, the neurotransmitter acetylcholine (the chemical that transmits impulses between nerves and muscles) is blocked by antibodies to its receptor. In Lambert-Eaton syndrome, however, the signal distortion is caused by an insufficient release of neurotransmitter by the nerve cell. As muscle contraction is continued, the amount of neurotransmitter may build up in sufficient quantities and result in increased strength.
The disorder may be associated with small-cell carcinoma of the lung and other malignancies as a paraneoplastic syndrome or with autoimmune disorders .
Signs and tests
An examination shows weakness or paralysis that improves with activity. Reflexes may be decreased. There may be muscle atrophy (loss of muscle tissue).
A Tensilon test can be positive. A baseline muscle strength evaluation is performed. After Tensilon (edrophonium) or other short-acting neurotransmitter is given, there may be a noticeable improvement of function. EMG and nerve conduction velocity tests may confirm the diagnosis, with improved function as contraction is prolonged or with repetitive stimulation.
Treatment
The primary goal of treatment is to identify and treat any tumors or other underlying disorders. 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.
Expectations (prognosis)
An important factor is whether there is an underlying tumor that can be treated. The symptoms of Lambert-Eaton syndrome may improve with treatment of the tumor and/or with suppressing the immune system. However, not all people respond well to treatment.