Lingual thyroid: thyroid tissue at the base of the tongue

The thyroid normally sits low in the front of the neck, where it makes hormones that regulate metabolism. A case report in the open-access literature describes ectopic thyroid as an uncommon embryological abnormality in which thyroid tissue is found somewhere other than its usual position. It says that of all ectopic thyroid, around 90% is found at the base of the tongue, and the report notes that the base of the tongue is the embryological place of origin of the thyroid.

In lingual thyroid the thyroid tissue has stayed at that site, so there may be a mass at the back of the tongue, pink and firm according to the report. The thyroid scan in the reported case showed no uptake in the usual position in the neck, which is why scans and blood tests are needed to understand how much thyroid tissue is working. The report states that the condition is rare, with a prevalence of about 1 in 100,000, though other estimates in the same report are higher and describe it as more common in females and on the left.

Many people have no symptoms and it is found incidentally. When symptoms occur they relate to the mass and to thyroid function. The case report lists the following, and the NHS page on dysphagia gives the general swallowing warning signs.

• Difficulty swallowing (dysphagia), choking or a feeling of a foreign body in the throat.

• A change in voice (dysphonia).

• Bleeding from the mass in some cases.

• Breathing difficulty and, occasionally, life-threatening airway obstruction.

• Signs of an underactive thyroid, such as tiredness, feeling cold and weight gain, listed by the NHS as symptoms of hypothyroidism.

The NHS says to ask for an urgent GP appointment or get help from NHS 111 if you have difficulty swallowing, cough or choke while eating or drinking, feel as if something is stuck in the throat after eating, or are short of breath after eating or drinking. For a baby or child with noisy breathing, trouble feeding or blue lips, or anyone with severe breathing difficulty, call 999; that is a general emergency principle rather than a statement from the cited pages.

A lump at the back of the tongue is better assessed by a clinician than monitored at home, because many conditions including cancer can cause lumps in the mouth and throat. See a GP for any lump that persists.

The case report describes diagnosis through clinical examination, thyroid scintigraphy with technetium (Tc 99m), ultrasound and laryngoscopy, which showed a spherical mass at the base of the tongue. It says the thyroid scan is the most important tool, with CT and MRI helping to define the extent and location, and that investigation should include thyroid function tests because the tissue may not make enough hormone. In the case described, the child had a raised TSH with a normal T4, a pattern called subclinical hypothyroidism.

The NHS explains how thyroid function is checked in general: a GP may arrange blood tests for thyroid-stimulating hormone (TSH) and thyroxine (T4) and may refer to a specialist. In an adult found to have a base-of-tongue mass the pathway is normally an ENT assessment with examination of the throat with a camera, supported by scans and blood tests.

The case report says treatment of a lingual thyroid depends on the sex and age of the patient and on the severity of symptoms and any ulceration or bleeding. It reports that patients with mild symptoms can be treated by medical suppression with levothyroxine, which could result in partial involution (shrinkage), while most cases received surgical treatment. It describes levothyroxine as a good option for people who are not suitable for surgery and have only obstructive symptoms, and notes that benign or malignant changes have occasionally been described in ectopic thyroid tissue, so symptomatic patients need an individual plan.

The NHS explains that an underactive thyroid is usually treated with levothyroxine tablets, usually for life, with regular blood tests to check the dose, and that being on the wrong dose can cause side effects such as feeling or being sick, diarrhoea, headaches or problems sleeping.

If there are airway symptoms, treatment is urgent and surgical expertise is needed. Decisions are made by an ENT surgeon and endocrinologist together.

In the case described, levothyroxine allowed the TSH to stabilise and the symptoms to improve over two years of follow-up, and surgical excision was not required. Outcomes for individuals depend on the size of the mass, symptoms and thyroid function. People with a lingual thyroid generally need long-term thyroid monitoring.

In the NHS the route is GP, then ENT and endocrinology, with nuclear medicine for scans. Private specialist consultations can offer the same investigations. The British Thyroid Foundation, a UK patient charity, provides general information for people with thyroid conditions.