What is Thymic Hyperplasia?
The thymus was recognized for its role in T-cell differentiation, or the process of creating specialized versions of white blood cells known as T-cells, only a few decades ago. Before the 1960s, it was thought to be a ‘vestigial’ organ, meaning it was assumed to be no longer useful. While the thymus is largely known as an organ that produces lymphocytes (a type of white blood cell) and for its role in T-cell differentiation, it also has a role in the endocrine system. This includes making thymosin, a hormone that helps regulate T-cell differentiation, and other factors that guide cell growth, maturation, and mineralization.
The thymus is the main place where T-cell lymphopoiesis, or the creation of T-cells, happens. This complex process is directed by thymic epithelial cells, which are cells in the thymus that help T-cells grow, mature, and survive. There are two main types of thymic epithelial cells – medullary and cortical, and each type has specialized sub-types with specific roles.
Thymic hyperplasia refers to the thymus growing larger due to an increase in cell numbers. The thymus usually reaches its largest size during puberty, then slowly gets smaller. Thymic hyperplasia is not always problematic, but if the thymus grows larger than expected for a person’s age, it can be a warning sign and should be investigated further.
What Causes Thymic Hyperplasia?
Thymic hyperplasia, the abnormal enlargement of the thymus gland, can occur due to two major reasons. They can either be congenital (present at birth) or acquired (developed later in life).
Congenital thymic hyperplasia happens because of issues with the neuroendocrine system, especially the hypothalamic-hypophyseal system, which is integral in maintaining the body’s internal balance. Depending on the gland’s functioning, it can make the immune system weak or overactive. If the thymus gland underperforms (hypofunctioning), it results in a deficiency of the immune system. On the other hand, if it overperforms (hyperfunctioning), it may lead to autoimmune diseases. These are conditions where the body’s immune system mistakenly attacks its own cells. The most common of these is myasthenia gravis, but conditions like graves’ disease and collagen vascular disorders have also been linked to it.
Thymic hyperplasia can also be acquired and result in either an underactive or overactive thymus gland. This typically occurs as a reaction to certain conditions like receiving chemotherapy, exposure to thermal burns, after cardiac surgery or after stopping oral steroids. This is because the thymus gland can be sensitive to changes in corticosteroids, which are a type of medications used to reduce inflammation in the body.
Risk Factors and Frequency for Thymic Hyperplasia
Thymic masses, or abnormal growths, commonly occur in the front part of the area between the lungs. Particularly among children, these are usually benign, or non-cancerous, and this condition is known as thymic hyperplasia.
Among adults, this condition is most frequently seen in people in their 40s and 50s. Both men and women are equally affected. Interestingly, this condition is more commonly found in people of Asian descent compared to other races.
For individuals suffering from a condition called myasthenia gravis, the discovery of thymic hyperplasia is often incidental and occurs in 50% to 70% of these patients. When looking specifically at the group of patients with myasthenia gravis, it’s found that 75% have some form of thymic disease.
- Among these, 85% have thymic hyperplasia,
- while 10% to 15% have a condition known as thymoma.
Signs and Symptoms of Thymic Hyperplasia
Thymic hyperplasia is a condition where the thymus gland in the chest grows larger than normal. Many times, people discover they have it while undergoing imaging for an unrelated chest issue. Since the thymus is near your lungs and major blood vessels, this overgrowth could cause symptoms like:
- Shortness of breath
- Dysphagia (difficulty swallowing)
- Cough
- Loss of appetite
- Weight loss
- Chest pain
If thymic hyperplasia grows large enough to press against the superior vena cava (a major vein near the top of your chest), it can lead to superior vena cava syndrome, which has symptoms such as:
- Swelling of face, neck, and upper chest
- Bluish color of the skin (cyanosis)
- Headaches
- Dizziness and feeling lightheaded
- Shortness of breath
- Bulging veins over the trunk
- Flushed face
- Noisy, harsh sounding breaths (stridor)
- Neurological signs
Another type of thymic hyperplasia, known as lymphofollicular thymic hyperplasia, is linked with autoimmune diseases such as myasthenia gravis and Graves’ disease, which can come with additional symptoms depending on the specific disorder.
Myasthenia gravis is an autoimmune disease involving the nerves and muscles. It results from issues with the transmission of signals between the neuromuscular junctions, leading to muscle weakness.
Graves’ disease is an autoimmune condition that affects the thyroid, causing overactive thyroid or hyperthyroidism. It was first noted to be associated with thymic hyperplasia in 1912. People with Graves’ disease might be diagnosed with thymic hyperplasia after a clinical evaluation and radiological tests. The treatment that improves the hyperthyroidism due to Graves’ disease also tends to reduce the size of the enlarged thymus.
Testing for Thymic Hyperplasia
If your doctor suspects thymic hyperplasia, which is when your thymus gland grows larger than normal, they may request specific lab tests and imaging studies to help confirm their diagnosis. One such lab test might look for a type of antibody—the body’s defense against foreign substances—correlated with myasthenia gravis, a disease that can often occur alongside thymic hyperplasia.
Thymic hyperplasia is typically discovered during imaging done for other health concerns or before some surgeries. For example, a chest x-ray might reveal changes in the chest area, or it might show a significant enlargement of the thymus in infants and young children. Nevertheless, it’s essential to know that a typical x-ray often doesn’t capture thymic hyperplasia because it usually appears ‘normal.’
In those cases, your doctor might order a contrast-enhanced computed tomography or CT scan. This type of imaging can provide a more detailed view of the chest area, revealing its exact location, the size of the enlargement, its relationship to nearby structures, and whether fluid, fat, or calcifications are present within the tissue. This information can be crucial if treatment or surgery might be needed.
Another imaging technique your doctor might use is the PET-CT scan, which could show the degree of fluorodeoxyglucose uptake–a special type of sugar used in this scan. Thymic hyperplasia typically only mildly ‘takes up’ this substance, unlike cancerous growths, which tend to take up a lot more.
A Magnetic Resonance Imaging or MRI scan might also help distinguish between thymic hyperplasia and cancer of the thymus gland. It can, however, be hard to tell the difference between a normal and an enlarged thymus using this method. In such instances, doctors follow a set of guidelines to help them.
Lastly, a biopsy or a small sample of the thymus tissue might be taken to study the cells within the gland to provide final clarification. In a normal setting, these cells would look normal under the microscope.
Treatment Options for Thymic Hyperplasia
Massive thymic hyperplasia refers to an unusually large thymus gland, which is an organ typically found in the chest, just behind the breastbone. If you have a diffusely enlarged thymus but aren’t experiencing any symptoms, your doctor will likely monitor your condition without any immediate treatment, as the risk of serious thymus-related diseases is quite low in this case. However, if the thymus becomes excessively large, a surgery to remove it might be necessary.
Lymphofollicular hyperplasia is another form of thymic hyperplasia. The treatment plan for this condition is dependent on the various signs and symptoms that you might be experiencing.
If you have developed a condition known as myasthenia gravis from the enlarged thymus, this affects your nerve-to-muscle connections and can cause weakness and other symptoms. Some medications like physostigmine or pyridostigmine may help manage these symptoms. They work by preventing the breakdown of a chemical called acetylcholine, which helps muscles contract and move. Another treatment option might involve corticosteroids, which are drugs that can reduce inflammation and improve symptoms. But how corticosteroids help with myasthenia gravis isn’t quite clear yet.
In some cases, a procedure called plasma exchange therapy might be used. This involves removing and cleansing your blood before returning it to your body, which can help with symptoms too. Additionally, removing the thymus gland completely, a procedure known as a thymectomy, might lead to symptom relief and reduced dependency on medications.
If thymic hyperplasia is due to Graves’ disease, a condition that causes your thyroid gland to produce too much thyroid hormone, it often gets better as the thyroid condition is managed and brought under control.
What else can Thymic Hyperplasia be?
When it comes to thymic masses, or growths on the thymus gland, they can be of different types which occur at different rates:
- Thymolipoma: This type of growth accounts for about 10% of thymic masses and is especially common in young adults.
- Thymoma: This accounts for 50% of masses in the front part of the area between the lungs (anterior mediastinal masses) and 20% of masses in the area between the lungs (mediastinal tumors).
- Thymic cysts: These are found in 3% of patients with a mass in the front part of the area between the lungs.
- Malignant Thymoma: This is a type of cancer on the thymus gland.
- Thymic carcinoid: This is a rare type of growth found in some people with a condition called MEN 1 syndrome.
- Thymic germ cell tumor: This accounts for 15% of masses in the front part of the area between the lungs. It is usually seen in young adults.
What to expect with Thymic Hyperplasia
Thymectomy, which is a surgical procedure to remove the thymus gland, has been confirmed to be effective in achieving complete and stable recovery in patients suffering from a condition called myasthenia gravis due to an enlarged thymus, which is also known as thymic hyperplasia.
For those having thymic hyperplasia associated with Graves’ disease, a condition that makes your thyroid gland produce too much thyroid hormone, their condition can improve quickly as the overactive thyroid is treated.
Overall, patients with thymic hyperplasia have a good outlook for recovery.
Possible Complications When Diagnosed with Thymic Hyperplasia
Superior vena cava syndrome is a condition caused when blood flow from the superior vena cava to the right atrium (part of the heart) is reduced. This can lead to several symptoms like swelling in the neck, face, and arms. It can also cause difficulty in breathing, coughing, headaches, dizziness, and feeling lightheaded. Its treatment is based on what’s causing the blockage; in cases where it’s due to thymic hyperplasia, a surgical procedure called thymectomy is typically done. Other possible conditions include Myasthenia gravis, and respiratory distress.
Symptoms and conditions:
- Swelling in the neck, face, and upper limbs
- Difficulty in breathing
- Coughing
- Headaches
- Dizziness
- Lightheadedness
- Condition: Thymic hyperplasia
- Condition: Myasthenia gravis
- Condition: Respiratory distress
Preventing Thymic Hyperplasia
People with thymic hyperplasia, a condition where the thymus gland grows larger than usual, can experience a variety of symptoms. These can include difficulties in breathing or swallowing, coughing, eye problems, or issues associated with the ‘superior vena cava’ which is a large vein that carries blood from your upper body to your heart. They may also have other symptoms like weakness and blurry vision that are often linked to an autoimmune disease (diseases where your own immune system mistakenly attacks your body) called ‘myasthenia gravis’. However, thymic hyperplasia is often discovered by chance when people have medical tests for other reasons.
When a person gets diagnosed, it’s important to provide emotional support and detailed, clear information about the condition, how it’s treated, what the future may look like and how it can affect their daily life.
For someone with thymic hyperplasia but who doesn’t show any symptoms (asymptomatic), they should be advised about future check-ups and what might happen if symptoms start to appear.
If a person is showing symptoms linked with pressure in and around the enlarged thymus (compressive symptoms), they should be explained what’s causing these symptoms and the potential requirement of a surgery (thymectomy) to take care of them. For those diagnosed with ‘myasthenia gravis’, it should be clearly explained about the relationship between their condition and thymic hyperplasia. If their symptoms don’t improve with medication and a procedure called ‘plasma exchange therapy’ (a process to clean your blood), they might need thymectomy.
For people with thymic hyperplasia along with an overactive thyroid gland due to ‘Grave’s disease’, it should be clearly explained to them that if the thyroid condition is controlled, the thymus enlargement will likely also get better.
It is important that the patient is given clear educational materials about the disease. These can include charts, diagrams, and videos that clarify every aspect of the disease, its treatment and ways to adjust their lifestyle as needed. The success of this approach is usually measured by how well the patient understands their condition and how satisfied they are with their care.
