Introduction:
Thyroid lymphoma is a rare type of thyroid cancer that is classified as primary and secondary thyroid lymphoma. Primary thyroid lymphoma starts in the thyroid gland, whereas secondary thyroid lymphoma starts in other parts of the body. People with Hashimoto’s thyroiditis are at a 60 % greater risk of developing thyroid lymphoma as compared to people without thyroiditis. Despite being cancerous, thyroid lymphomas are highly treatable and have a good prognosis.
What Is the Thyroid Gland?
The thyroid is a small yet significant endocrine gland responsible for the production and secretion of thyroid hormones. These hormones include triiodothyronine (T3), thyroxine (T4), and calcitonin. The thyroid gland is shaped like a butterfly consisting of two lobes that are connected in their lower one-third parts. The two lobes are bridged by a band of tissues called the thyroid isthmus. The thyroid is crucial for regulating growth, development, metabolism, protein synthesis, maintaining calcium, balance, and many other important functions of the body. Any imbalance in the levels of thyroid hormones can lead to several thyroid disorders like hypothyroidism (underactive thyroid), hyperthyroidism (overactive thyroid), thyroiditis (inflamed thyroid), goiter (lump in the thyroid), thyroid nodules, thyroid cancer, etc.
What Is a Thyroid Lymphoma?
Lymphoma can be defined as cancer that originates in the lymphocytes, the infection-fighting white blood cells (WBC) of the immune system. Lymphoma starts in the lymphatic system (part of the immune system) and spreads throughout the body. Lymphoma is most commonly found in lymph nodes, although it can also emerge from lymphocytes in the thyroid gland in rare situations. Thyroid lymphomas are rare and more prevalent in females as compared to males. The average age of onset is 60 years.
What Are the Types of Thyroid Lymphoma?
Thyroid lymphomas are classified as :
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Primary Thyroid Lymphoma: Primary thyroid lymphomas originate in the thyroid gland and, from there, spread to the lymph and other organs of the body.
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Secondary Thyroid Lymphoma: Secondary thyroid lymphoma starts in the lymph nodes or other organs, followed by a subsequent spread in the thyroid gland.
What Causes Thyroid Lymphomas?
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The exact cause of why cancer develops in any individual is unknown; however, thyroid lymphomas often develop in individuals with a history of pre-existing Hashimoto’s thyroiditis. Hashimoto’s thyroiditis is an autoimmune condition (when the body’s immune system starts attacking healthy cells) characterized by inflammation of the thyroid gland. When compared to people who do not have thyroiditis, the risk is over 60 times higher.
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Theories suggest that chronic stimulation of antigens after Hashimoto’s thyroiditis leads to a sudden and rapid division of lymphoid tissue, which eventually undergoes a mutation and causes the development of lymphoma.
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Graves' disease, goiter, radiation exposure, and chromosomal abnormalities are not linked to the development of thyroid lymphomas.
Is Thyroid Lymphoma a Common Condition?
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Thyroid lymphomas are rare, and it constitutes only one to two percent of all thyroid cancers.
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Thyroid lymphomas constitute less than two percent of all lymphomas in the body.
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This rate of incidence has been steadily increasing annually by 3.2 %.
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Thyroid lymphomas are more common in women as compared to men. The risk of developing thyroid lymphoma is three to four times higher in women.
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The average age of onset of thyroid lymphoma is between 60 to 65 years, and it is more prevalent among older people.
What Are the Symptoms of Thyroid Lymphoma?
The common signs and symptoms of thyroid lymphoma include;
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Rapidly growing thyroid mass.
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The thyroid gland, on physical examination, will appear firm, diffusely enlarged, and immobile.
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Swelling in the lymph nodes of the neck.
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Dyspnea or difficulty in breathing due to compression of the trachea (windpipe) by the enlarged thyroid.
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Stridor (whistling sound while breathing) due to compression of the windpipe.
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Dysphagia or difficulty in swallowing due to compression of the esophagus (food pipe).
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Pain in the neck.
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Swelling in the face.
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Hoarseness of voice.
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B-cell lymphoma symptoms - fever, night sweats, and weight loss can occur in up to ten percent of cases.
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Symptoms of hypothyroidism may be seen in some patients due to Hashimoto’s thyroiditis. These symptoms include; tiredness, cold intolerance, constipation, weakness, dryness of skin, dryness of hair, irregular menstrual cycles in women, etc.
How Is Staging for Thyroid Lymphomas Done?
The Lugano staging system is used to determine the spread of thyroid lymphomas in the body:
How Are Thyroid Lymphomas Diagnosed?
The diagnosis of thyroid lymphoma is made in the following ways:
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Blood Examinations: Blood tests are done to evaluate the levels of thyroid hormones, thyroid-stimulating hormone (TSH), and antithyroglobulin. However, these blood examinations are not very helpful because several other thyroid conditions cause hormone imbalance. In the case of thyroid lymphomas, the levels of thyroxine and triiodothyronine will be decreased, and thyroid-stimulating hormones will be increased. In addition, there will be an elevation of antithyroglobulin or antithyroid antibodies due to Hashimoto’s thyroiditis.
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Imaging Tests: Thyroid ultrasound, MRI (magnetic resonance imaging), and CT (computed tomography) scans are used to determine the extent of the disease, spread outside the thyroid gland, invasion of the windpipe, and lymph involvement. 18-fluorodeoxyglucose (radiotracer) PET scan (positron emission tomography) is done to evaluate the increased uptake by the thyroid gland.
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Fine Needle Aspiration (FNA): A sample of tissues is collected with the help of fine-needle aspiration and sent to the laboratory for evaluation. FNA is more helpful in diagnosing big lymphomas. A core biopsy is recommended for a definitive diagnosis of thyroid lymphoma if it is suspected.
How Are Thyroid Lymphomas Treated?
The treatment of thyroid lymphoma depends upon its type and stage of the extent of cancer. The following treatment modalities are used to treat thyroid lymphomas:
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Combined treatment with chemotherapy and radiotherapy is preferred over only chemotherapy for limited-stage thyroid lymphomas.
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Chemotherapy alone is preferred in the case of advanced-stage thyroid lymphoma.
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The chemotherapy regimen used - Rituximab-Cyclophosphamide, Doxorubicin, Vincristine, and Prednisolone.
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Due to the potential surgical complications and no added benefit compared to chemoradiation therapy, surgery is generally not suggested except for diagnostic biopsy.
What Are the Possible Complications of Thyroid Lymphomas?
Possible complications of untreated thyroid lymphomas are:
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Airway obstruction due to compression of the windpipe by the enlarged gland.
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Superior vena cava syndrome (a set of problems caused when the blood flow through the superior vena cava vein is reduced).
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Obstruction of the food pipe.
Complications occurring due to the treatment of thyroid lymphoma are:
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Radiation-induced hypothyroidism.
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Radiation-associated malignancies (cancer) of the thyroid and other organs.
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Nerves outside the brain and spinal cord get damaged due to the use of Vincristine.
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Congestive heart failure due to Doxorubicin.
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Bladder cancer due to the use of Cyclophosphamide during chemotherapy.
Conclusion:
The prognosis and treatment of thyroid lymphoma depend on the type of lymphoma and the extent of its spread. Thyroid lymphomas during the early stage are easily treatable and have a good prognosis as compared to advanced-stage thyroid lymphomas. When thyroid lymphoma spreads to lymph nodes and other organs of the body, they become more difficult to treat. However, thyroid lymphomas, in general, have an excellent prognosis and a 91 % survival rate. Combined treatment with radio and chemotherapy is extremely effective in limiting cancer.
