A 67-year-old man with lung cancer is seen by the palliative-care team after complaining of severe fatigue and weakness. He is now unable to stand from sitting, has problems chewing and gets occasional double vision. Examination shows normal power in the hands and feet, but weakness of the girdle muscles and an oculomotor nerve palsy on the right with ptosis. The doctor is surprised that the weakness improves after repeated demonstrations to colleagues. Most likely diagnosis is:
C. LambertEaton syndrome
Correct Answer: C. Lambert-Eaton Syndrome
Lambert-Eaton syndrome is a rare syndrome affecting of neuromuscular junction. Although the etiology and the clinical findings of the disease may resemble myasthenia gravis, but there are many substantial differences between clinical presentations and pathogenetic features of two disorders.
Lambert Eaton Syndrome is usually a solitary diagnosis but lung cancer (small-cell histology) may accompany the disease in some cases. It may also be associated with cancers such as lymphoma, non-Hodgkin's lymphoma, T-cell leukemia, non-small cell lung cancer, prostate cancer, and thymoma.
In both conditions, the disease is of autoimmune origin, with antibodies directed against the antigens of the neuromuscular junction. In 1989, the previously anticipated antibodies were demonstrated to be directed against presynaptic calcium channels and are responsible for the efficient release of acetylcholine.
The antibodies prevent normal function of calcium channels and thus prevent the release of acetylcholine.
The picture is therefore very similar to myasthenia gravis, typically with proximal weakness and often ocular or bulbar palsies. However, unlike myasthenia gravis the weakness often improves with repeated muscle contraction. Approximately 50% of cases have an identifiable malignancy.
Other neural autoantibodies associated with small cell carcinoma include those to potassium channels leading to neuromyotonia (Isaacs syndrome) and those leading to cerebellar ataxia and other peripheral neuropathies.
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