The Thymus Gland
What is the thymus gland and what diseases commonly affect it?
The thymus is a small fatty gland situated behind the sternum, directly in front of the heart and aorta. It is involved in recognizing what in the world belongs to you, and what is a potentially nasty alien (virus, protein, etc.). If you are born without one, you die pretty soon after birth. However, after development in the womb, and a couple of years of sampling of yourself and the environment (maybe up to 5 years old), the thymus shrivels up into small piece of fat and is completely useless thereafter.
The gland goes “haywire”! This leads to a condition called myasthenia gravis (also known as auto-immune myasthenia). Put simply, the thymus directs the immune system to attack the neuromuscular junction where messages are carried from your brain (via the nerves) to the muscles. This condition leads to severe weakness of affected muscles, especially with repeated use over a short time. This is known as fatigability, and mostly affects the eyes (droopy eyelids, double vision), muscles of chewing and swallowing, or can affect the whole body, including muscles of breathing.
The gland develops a tumour! The most common tumour is called a thymoma. A thymoma can behave itself for many years (maybe never bothering the person) or can be quite aggressive. In this case it can grow rapidly, invade body organs nearby and spread to the chest or elsewhere. About 20% of patients with a thymoma will also develop myasthenia gravis (also known as thymomatous myasthenia). If the tumour is taken out completely, about 30-40% of patients will be cured of this type of myasthenia.