Myasthenia Gravis vs. Lambert Eaton Syndrome ?

Question:
What is the difference between Myasthenia Gravis and Lambert-Eaton syndrome? How do doctors differentiate between the two in diagnosis? Is the treatment similar?


Answer:
Myasthenia gravis causes muscle weakness that patients usually appreciate becoming significantly worse with activity. Double vision, swallowing and speaking abnormalities, and difficulty walking and using the arms are common symptoms. Lambert-Eaton may produce similar symptoms, but double vision is less common. Muscle aches are more common and patients often have dry mouth. Patients may also have impotence, constipation, impaired sweating, and blurred vision.
Myasthenia gravis is caused by antibodies against acetylcholine receptor and compromise the muscle side of the nerve-muscle communication point. Lambert-Eaton syndrome appears to be caused most often by antibodies to calcium channels of the nerve. Lambert-Eaton is often triggered by the development of a lung cancer.


An EMG test can differentiate between myasthenia gravis and Lambert-Eaton. Also, blood tests for antibodies may also help with their differentiation.


Many of the treatments for the disorders are similar, although patients with Lambert-Eaton often do not respond as well. Thymectomy is not used .



Myasthenia Gravis and Lambert Eaton Syndrome are two types of neuromuscular junction (NMJ) disorders that every physician should know to distinguish. They are both autoimmune diseases, type II hypersensitivy reactions. Myasthenia gravis is the most common NMJ disorder; it is the result of auto antibodies against the acetylcholine (ACh) receptors in the skeletal muscle. The common clinical presentation is: ptosis, diplopia, and general weakness. These symptoms get worse with muscle use and are reversed using acetylcholinesterase (AChE) inhibitors. Lambert Eaton Syndrome is caused by auto antibodies against the presynaptic calcium channels, resulting in decreased ACh release. The symptoms improve with muscle use, and there is no effect with the use of AChE inhibitors alone (there is no ACh in the synaptic cleft). Myasthenia gravis is associated with thymomas and Lambert Eaton Syndrome is associated with paraneoplastic syndromes, especially with small cell lung carcinoma.


In a myasthenia gravis patient, the weakness does not improve with exertion And why in Lambert-Eaton myasthenic syndrome patient, it does improve with exertion?
In patients with MG repetitive stimulation of a motor nerve will at first cause the production of a normal summated muscle action potential whose amplitude will, however, decrease through progressively increasing "fatigue" of neuromuscular transmission. In EL syndrome (perhaps small cell carcinoma of the lung) due to the summated muscle action potential is at first small, but is progressively normalized, because with repetitive stimulation increasing amounts of Ca+ are accumulated in the nerve endings. In MG Ab are against the Ach receptors (postsynaptic), whereas in EL the Ab are directed against Ca+ channels of the end plate (presynaptic).

Response by:

Henry J Kaminski, MD Formerly, Professor of Neurology Department of Neurology  School of Medicine  Case Western Reserve University