From the Guidelines
Laboratory evaluation of thymus hyperplasia should include a combination of imaging studies, such as CT scans and MRI, as well as blood tests, including complete blood counts, comprehensive metabolic panels, and specific antibody tests like anti-acetylcholine receptor antibodies, to confirm the diagnosis and rule out associated conditions. The initial assessment should prioritize distinguishing between thymic hyperplasia and thymoma, with CT scans being the preferred initial imaging modality due to their ability to clearly visualize the thymus and differentiate between hyperplasia and tumors 1. In cases where the CT scan is doubtful or when evaluating cystic lesions, MRI is recommended as it can help differentiate thymic tumors from hyperplasia, especially by detecting microscopic fatty infiltration through chemical-shift MRI 1. Blood tests should include a systematic immunological check-up, comprising complete blood cell counts with reticulocytes and serum protein electrophoresis, as well as tests for anti-acetylcholine receptor and anti-nuclear antibodies to assess for associated autoimmune diseases like myasthenia gravis 1. Thyroid function tests are also important since thyroid disorders can be associated with thymic changes. For suspected myasthenia gravis, additional tests such as electromyography and repetitive nerve stimulation studies may be necessary. Notably, PET scans are generally not recommended for assessing thymic masses unless there is a concern for malignancy or in the staging of aggressive tumors 1. These evaluations are crucial for determining the nature of the thymic hyperplasia and guiding appropriate management decisions, prioritizing the patient's morbidity, mortality, and quality of life. Key considerations include:
- The use of CT scans as the primary imaging modality
- The role of MRI in specific cases, such as differentiating thymic tumors from hyperplasia
- The importance of systematic immunological check-ups
- The selective use of PET scans
- The consideration of thyroid function tests and tests for myasthenia gravis when relevant.
From the Research
Laboratory Evaluations for Thymus Hyperplasia
The laboratory evaluations for thymus hyperplasia include various tests to diagnose and confirm the condition. Some of the key evaluations are:
- Histological and flurocytometric analyses of an incisional biopsy of the thymus, which can reveal findings consistent with true thymic hyperplasia 2
- Fluorodeoxyglucose positron emission tomography/Computed tomography (FDG-PET/CT) scans, which can show stable findings consistent with true thymic hyperplasia 2
- Computed tomography (CT) scans, which can measure thymic volume and assess thymic enlargement 3
- Pneumomediastinography (PMG), which can demonstrate thymus hyperplasia and/or thymoma in patients with autoimmune diseases such as ulcerative colitis and myasthenia gravis 4
- Laboratory tests, such as complete blood counts and blood chemistry tests, to rule out other conditions and assess overall health 5
Diagnostic Considerations
When evaluating thymus hyperplasia, it is essential to consider the clinical context and radiologic studies, such as CT scans, to diagnose the condition and rule out other potential causes of thymic enlargement 3. The diagnosis of thymic hyperplasia can be made by exclusion, and awareness of the association between thymic hyperplasia and conditions such as Graves' disease can help prevent unnecessary thymic evaluation and surgery 3.
Histological Findings
The histological findings of thymic hyperplasia can vary, but may include:
- Germinal centers in the thymus, which can occur in apparently normal thymuses in both children and adults 6
- Lymphoepithelial sialadenitis (LESA)-like thymic hyperplasia, a rare disorder characterized by an unusual type of thymic hyperplasia strongly resembling LESA of the salivary glands 5
- Thymic parenchyma hyperplasia and medullary lymphoid hyperplasia, which have been described in association with Graves' disease 3