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Regarding myasthenia gravis:

True / False

It is associated with hyperthyroidism Incorrect answer selected

It is usually due to defective release of acetylcholine from presynapticnerve terminals Correct

Hyperplasia of the thymus is present in 65% of cases Correct

It may be caused by penicillamine Correct

The severity of the disease is related to the level of antireceptor antibodies Incorrect answer selected

Explanation

Myasthenia gravis (MG) is an autoimmume disease characterised by skeletal muscle weakness and increased fatigability.

There is an immune response directed against acetylcholine receptors (AChR) and occasionally to muscle-specific kinase (MuSK) at the neuromuscular junction. Antireceptor antibodies are found in up to 90% of patients, but the severity of the disease is unrelated to the level of antireceptor antibodies.

It may occur in neonates born to affected mothers and may be caused by penicillamine and other drugs.

As an autoimmune condition it is associated with other autoimmune disorders including thyroid dysfunction (rarely).

Eaton-Lambert syndrome produces a myasthenic-like syndrome and is usually associated with bronchial carcinoma but can rarely be due autoimmune disease. It is due to defective release of acetylcholine from presynaptic nerve terminals, and has normal post-synaptic receptors.

Hyperplasia of the thymus is present in 65% of cases of myasthenia gravis. There are many possible 'tumours' of the thymus, including:

thymoma

thymic carcinoma

neuroendocrine tumours

thymic germ cell tumours, and

thymic lymphomas

D-penicillamine is a therapeutic agent for several diseases, but can also induce a number of immune-mediated disorders, including MG, as a side-effect.

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