32. Thyroiditis, malignant tumours of the thyroid gland
Hashimoto thyroiditis
Hashimoto thyroiditis, also called chronic autoimmune hypothyroidism is an autoimmune condition characterised by CD8-mediated destruction of the thyroid parenchyme. It’s the most common cause of chronic hypothyroidism in western countries, affecting 3 – 5 per 10 000. It mostly affects middle-aged females.
It’s associated with other autoimmune diseases and with HLA-DR5.
Clinical features
In the early phase thyrotoxicosis develops as the destroyed cells release preformed hormones, sometimes called “hashitoxicosis”. In this phase, there’s a non-tender and painless goitre.
Later, hypothyroidism occurs in the chronic phase, as the number of cells decreases. In this phase, the thyroid may be normal or small. Hashimoto causes painless goitre.
The patient may present in any of these stages. The goitre may be diffuse or nodular.
Diagnosis and evaluation
The following features are typical for Hashimoto:
- Typical clinical features
- Ultrasound findings (inhomogenous, hypoechogenic thyroid)
- Normal leukocyte count
- Moderately elevated ESR
- Initial thyrotoxicosis followed by hypothyroidism
- Elevated anti-thyroid antibodies (anti-TPO, anti-Tg)
The anti-thyroid antibodies are the main factors in the diagnosis of Hashimoto thyroiditis. Ultrasound is rarely indicated in the evaluation of Hashimoto thyroiditis.
Treatment
The treatment of Hashimoto thyroiditis is lifelong L-thyroxine replacement therapy, as for other causes of hypothyroidism. Immunosuppressants are not helpful in the treatment of Hashimoto thyroiditis.
Subacute granulomatous thyroiditis
De Quervain thyroiditis, also called subacute granulomatous thyroiditis or giant cell thyroiditis, is a transient, self-limiting viral infection of the thyroid that occurs some weeks after a viral upper respiratory tract infection. Granulomas are present in the thyroid, hence the name.
It’s a moderately frequent disorder with seasonal fluctiations. It mostly affects middle-aged females.
Clinical features
The symptoms are usually preceded by an upper respiratory tract infection a few weeks prior. The typical symptoms of de Quervain thyroiditis include:
- Neck pain irradiating to the ear
- Painful goitre
- Fever
- Malaise
As in other cases of thyroiditis, there is an initial phase of thyrotoxicosis followed by a later phase of hypothyroidism.
Diagnosis and evaluation
Diagnosis is based on:
- Typical clinical features
- Ultrasound findings (inhomogenous, hypoechogenic thyroid)
- Normal leukocyte count
- Extremely high ESR
- Initial thyrotoxicosis followed by hypothyroidism
- No anti-thyroid antibodies
Radioactive iodine uptake test shows low iodine uptake, but this test is rarely indicated.
Treatment
For management of pain, NSAIDs are used. If insufficient, a short course of corticosteroids lasting 2 – 3 months is effective.
In the thyrotoxic phase, beta blockers may be useful for symptomatic therapy, while in the hypothyroid phase thyroxine substitution is indicated.
Prognosis
The thyrotoxicosis rapidly decreases and progresses to hypothyroidism, which is transient and normalises over 6 months in most cases. 10% retain permanent hypothyroidism.
Postpartum thyroiditis
Postpartum thyroidits is a form of autoimmune subacute thyroiditis which affects postpartum women. It’s likely that postpastum thyroiditis is an accelerated form of Hashimoto thyroiditis which is triggered by the pregnancy, as 50% of cases were anti-TPO positive ahead of pregnancy.
It occurs in 5 – 10% of deliveries.
Clinical features
It develops within 6 months after delivery. The goitre is painless. As in other cases of thyroiditis, there is an initial phase of thyrotoxicosis followed by a later phase of hypothyroidism.
Diagnosis and evaluation
Diagnosis is based on:
- Typical clinical features
- Ultrasound findings (inhomogenous, hypoechogenic thyroid)
- Normal leukocyte count
- Extremely high ESR
- Initial thyrotoxicosis followed by hypothyroidism
- Presence of anti-thyroid antibodies (anti-TPO, anti-Tg)
Radioactive iodine uptake test shows low iodine uptake, but this test is rarely indicated as it cannot be performed in a nursing patient.
Treatment
Treatment is supportive. In the thyrotoxic phase, beta blockers may be useful for symptomatic therapy, while in the hypothyroid phase thyroxine substitution is indicated.
Prognosis
Many (30-50%) develop permanent hypothyroidism. If not, there’s a 70% risk of relapse after the next pregnancy.
Thyroid nodule
Discovery of a thyroid nodule, a nodule in the thyroid gland, either by the patient or incidentally during physical examination, is a common presentation of thyroid neoplasms or cysts. 95% of thyroid nodules are benign.
Some thyroid tumours produce thyroid hormones, causing hyperthyroidism, in which case they’re called “toxic”.
Etiology
These are the most common causes of thyroid nodule:
- Benign thyroid nodule
- Follicular adenoma
- Toxic adenoma
- Thyroid cyst
- Malignant thyroid nodule
The most common thyroid nodule is the follicular adenoma. Follicular adenomas are derived from the follicular epithelium. They’re solitary, well-circumscribed masses that may give rise to painless uninodular goiter.
Toxic adenomas are follicular adenomas which produce thyroid hormones. These toxic adenomas have acquired a gain-of-function mutation in the TSH receptor complex, allowing the follicular cells to be stimulated even in the absence of TSH. They’re common in iodine deficient regions, but very rare in iodine sufficient regions.
Multinodular goitre (MNG) is a complication of long-standing nodular goitre which occurs when multiple nodules develop. These nodules may be toxic (toxic multinodular goitre) or non-toxic (non-toxic multinodular goitre).
Diagnosis and evaluation
The following modalities are used in the evaluation of thyroid nodules:
- Ultrasound
- Thyroid scintigraphy – shows the distribution of thyroid function
- FNAB
- CT
When a new thyroid nodule is found, TSH should be measured, and the nodule should be examined with ultrasound. If the ultrasound shows features suspicious for malignancy, a fine needle aspiration biopsy (FNAB) is usually performed to determine the dignity, if the nodule is over a certain size. If the nodule is too small for FNAB, it’s monitored regularly.
If TSH is low, thyroid scintigraphy is performed to look for whether the nodule is hot (produces hormones) or cold (doesn’t). A single hot nodule is likely a toxic adenoma, while multiple hot nodules usually refers to a toxic multinodular goitre. Hot nodules are rarely malignant.
Treatment
Toxic adenoma and toxic multinodular goitre are treated with radioiodine therapy or surgical removal. Compensated toxic adenoma is managed with observation only.
Malignant cold nodules are treated with surgery. Benign cold nodules are treated with observation if < 3 cm, and surgery if > 3 cm.
Thyroid cancer
Thyroid cancer is rare and generally has a good prognosis. The incidence has increased markedly in the recent decades, but the mortality remains low. Thyroid cancer is rarely hyperfunctional, meaning that it rarely causes hyperthyroidism.
The differentiated types are the most common, and these types rarely metastasize and have a good prognosis. If they do metastasise, it’s frequently to the cervical lymph nodes. The treatment for any type of thyroid carcinoma is total thyroidectomy.
Etiology
The major risk factor predisposing to thyroid cancer is previous exposure to ionizing radiation at the area of the neck, especially during the first 2 decades of life. Therefore it’s not strange that the incidence of papillary carcinomas among children exposed to the chernobyl disaster was high. Dietary deficiency of iodine is also linked with follicular thyroid carcinoma.
Medullary carcinoma is associated with MEN2A and MEN2B.
Classification
We classify the malignant thyroid tumors according to their differentiation. Here they are in order from most to least common:
| Tumor type | Cell of origin |
|---|---|
| Differentiated | |
| Papillary carcinoma | Thyroid follicular cell (= epithelial cells) |
| Follicular carcinoma | Thyroid follicular cell |
| Poorly differentiated | |
| Medullary carcinoma | Parafollicular cell (= C cells) |
| Anaplastic carcinoma | Thyroid follicular cells |
Papillary carcinoma is the most frequent type by far as it accounts for 80% of all thyroid carcinomas. It has a very good prognosis.
Medullary carcinomas are associated with multiple endocrine neoplasia type 2a and 2b (MEN-2). It has a poor prognosis.
Anaplastic carcinoma is most frequent in elderly. It’s one of the most aggressive cancers. It has an average 6 months survival.
The tumour marker for thyroid cancer is thyroglobulin, except for medullary carcinoma, for which calcitonin is the tumour marker.
Clinical features
Thyroid carcinomas are usually discovered as nodular, painless goiters. The nodule is fixed and rapidly growing, and may cause symptoms of compression of the trachea or oesophagus.
Diagnosis and evaluation
See evaluation of thyroid nodules.
Treatment
Thyroid cancer is treated with total or near-total thyroidectomy with or without neck dissection. For well-differentiated cancers, radioactive iodine ablation and TSH suppression therapy are used after the surgery. TSH is a growth factor and so suppression of it prevents tumour recurrence.
Poorly differentiated cancers respond to neither radioactive iodine ablation nor TSH suppression. Instead, poorly differentiated cancers are treated with adjuvant radiation and/or chemotherapy.
After total thyroidectomy, thyroid hormones must be substituted for life.