Hypothyroidism caused by a nonvisible lingual thyroid

More documents

Recommendations

Info

throat (ENT) examination. Routine laboratorytests revealed a mild normocytic, normochromicanemia (hemoglobin, 12.7 g/dL; mean corpuscularvolume [MCV], 86 fL; mean corpuscular hemoglobin[MCH], 26.2 pg/cell) and mildly elevatedcholesterol (207 mg/dL). Similar hemoglobin valueswere observed in the past, and his ferritinvalues were within normal limits. Thyroid functiontests revealed significantly elevated thyroidstimulatinghormone (TSH) levels with free serumtriiodothyronine (FT 3 ) and free serum thyroxine(FT 4 ) at the lower limit of normal values. Followupthyroid function tests revealed elevated TSHand low FT 4 , with FT 3 being at the lower limit ofnormal values He was restricted from continuedflying duty pending the completion of work-up ofhis thyroid function abnormality.His chest X-ray was found to be normal. Anultrasound examination of the neck revealed atrophyof both thyroid lobes with nonhomogenousconsistency and no lymphadenopathy. A technetium-99mscan revealed uptake at the tonguebase with no uptake at the neck or at other locations.A diagnosis of lingual thyroid was made,and L-thyroxine treatment was begun with a progressivedecrement in TSH values and disappearanceof the cough.DISCUSSIONLingual thyroid is the term applied to a mass ofectopic thyroid tissue located at the tongue baseat the midline, usually between the circumvallatepapillae and the epiglottis, in the area of theforamen cecum. It is believed to result from defectivedescent of the thyroid anlage from itsembryonic position at the base of the tongue to itsnormal pretracheal location, which usually occurson weeks 3 to 7 of embryonic development. Defectsin migration may lead to locations of thethyroid gland in other midline structures such asthe trachea, the esophagus, or near the hyoidbone. Hickman 1 reported the first case of lingualthyroid in 1869, and 400 cases have been describedin the literature to date. This is the mostcommon benign mass found at the junction of theanterior two thirds and the posterior one third ofthe tongue. Postmortem studies indicate that upto 10% of people have thyroid tissue remnantsnear the base of their tongue, 2,3 although clinicallyapparent lingual thyroid is an unusualcondition, with a few hundred cases reported inthe literature. The estimated frequency of clinicallysignificant lingual thyroid varies between1/3000 and 1/10,000. 4 In 70% of these cases, thelingual thyroid is the only functional thyroidtissue. 5 Hypothyroidism is observed in an estimated33% of the cases and is commonly precipitatedby increased physiologic demands. 6 Thisentity is much more prevalent in females, with amale-to-female ratio of 1:3 to 1:8. 7The pathogenesis of this condition remainsunknown. It is postulated that maternal antithyroidantibodies may arrest the gland’s descentand predispose the patient to poor thyroid functionlater in life. 8 The incidence of thyroid diseaseamong family members of patients with lingualthyroid is higher than among the populationat large. 9The symptoms of lingual thyroid are variableand depend on the patient’s age. Infants andyoung children are usually diagnosed on routinescreening and often have failure to thrive andmental retardation. Older children, adolescents,and adults are diagnosed after the onset of obstructivesymptoms, such as dysphagia, dysphonia,dyspnea, a cough worse on lying down, orlocal hemorrhage. Glandular hypertrophy occursin these populations as a response to the rise inTSH levels that is generated by the increase inmetabolic demand for thyroid hormone that occursin situations such as puberty, pregnancy,trauma, infection, or menopause. 10The initial evaluation of a lingual thyroidinvolves a thorough head and neck examination.The mass appears light pink to bright red or blue,and its surface can be smooth or irregular.Flexible or rigid endoscopy of the upper airwayis performed to determine the size of the thyroidand airway patency. Laboratory evaluationshould include thyroid function tests, which frequentlydemonstrate normal to low levels of T3and T4 and low levels of TSH and thyroglobulin.Hyperthyroidism, although rare, has been reported.11 A technetium scan should be used toconfirm the diagnosis. These scans frequentlyshow radionuclide activity at the level of themouth and no apparent activity in the normalposition in the neck. CT provides an accuratemethod of determining the gland size, and it canbe performed without contrast, because the thyroidtends to accumulate iodine. 12 MRI is consideredthe method of choice to study lingualthyroids in a noninvasive way because of its multiplanarcapabilities and its high degree of softtissue resolution, which result in better delineationof the lesion. 13 Ultrasound is less dependableand is used to follow an enlarging component of996 Hypothyroidism from Nonvisible Lingual ThyroidHEAD & NECK November 2004
a thyroid gland without the need for additionalionizing radiation.Malignant degeneration in lingual thyroidseems to be the same as for orthotopic thyroidtissue. 3 Lingual thyroid carcinoma has been describedin patients from the age of 12 to the ageof 86, with the mean age of presentation in thethird decade. 14 No risk factors have been describedin the literature, but it is assumed thatthey are the same as those for malignancy of acervical thyroid (x-ray exposure of the head, neck,or mediastinum in infancy or childhood). Thereare no clinical findings that can differentiatelingual thyroid carcinoma from a symptomaticlingual thyroid. Therefore, it is recommendedthat biopsy or aspiration be taken in every case oflingual thyroid to rule out thyroid carcinoma. 15The natural history of lingual thyroid carcinomais unknown because of the rarity of this condition,yet most cases described in the literature did notextend beyond the tongue.Treatment of lingual thyroid is controversial.All patients should receive lifelong thyroxinesuppression, even those with small and asymptomaticlingual thyroids, because this will preventthe gland’s enlargement, diminish the risk ofmalignancy, and prevent hypothyroidism. 16 Theectopic thyroid tissue can be ablated by a therapeuticdose of 131 I. This modality is safe andeffective and should be included in the algorithmwhen formulating a treatment plan for the symptomaticpatient. 17 Surgery is reserved for thosewhose initial symptoms worsen while on suppressivetherapy. Surgery becomes crucial in cases ofrecurrent hemorrhage, severe dysphonia or dysphagia,or significant airway compromise. CT andMRI are helpful in determining the best approachfor total gland excision. Complete excision ofthe gland is difficult, and in most cases, thereare remnants left at the base of the tongue, whichhave the potential to enlarge in the future unlesssuppressed with thyroid replacement therapy.Our case is unique in several aspects. Therelatively late age of presentation of our patientis surprising, because most cases of lingual thyroidare diagnosed at times of increased metabolicdemands. Our patient was a militaryaviator, who was certainly exposed to increasedmetabolic demands, whether while being a studentaviator or while performing certain militarymissions. Previous reports linked stress anddevelopment of symptoms in patients withlingual thyroid, and there are descriptions ofsymptomatic cases linked to enrollment andtraining in the army. 16 Our patient completeda difficult army training program with no apparentsymptoms. No apparent cause of increasedmetabolic demands was identified before hisclinical presentation, and we do not have a goodexplanation for the timing of his symptoms. Thepatient did gain 4 kg in weight in the monthsbefore the diagnosis. This weight gain may haveincreased his metabolic demands and caused hislingual thyroid to become symptomatic, but theymay also have been a result of his hypothyroidism.The presenting symptom of prolonged cough inour patient is also unique. Most cases described inthe literature of adults with symptomatic lingualthyroid manifested as dysphagia, dysphonia, aforeign body sensation in the throat, bleeding, orintermittent respiratory obstruction. A cough,which worsens on lying down, has been describedbut is rare. 11 In our patient, no other cause for thecough was identified, and the cough improved onstart of treatment; therefore, we assume that thecough was related to the lingual thyroid, althoughthe lingual thyroid was not visible on the ENTexamination. The laboratory evidence of hypothyroidismand the technetium scan eventuallyled to the diagnosis, despite a normal ENT examination.We recommend that thyroid functiontests be included in the laboratory evaluation ofpatients with complaints of the upper airway,including prolonged cough. Those with impairedthyroid function tests should undergo a thoroughevaluation for a lingual thyroid by an otolaryngologist.Even in cases of a normal ENT examination,a technetium scan should be performed,because clinically significant lingual thyroid maybe difficult to diagnose solely on clinical grounds.Should a lingual thyroid be found on a radionuclidescan, we believe that treatment withlevothyroxine should be started to suppress thethyroid gland. In most cases, this treatment willcause decrement of the gland and resolution ofsymptoms. If symptoms fail to resolve or thegland fails to decrease in size, a biopsy should betaken to rule out a malignancy.CONCLUSIONSLingual thyroid is a rare entity that has the potentialto present at any age. The clinical presentationin adults is variable, but most patientshave symptoms that result from local irritation.The combination of such complaints and disturbancesin thyroid function tests should promptthe physician to search for a lingual thyroid byHypothyroidism from Nonvisible Lingual Thyroid HEAD & NECK November 2004 997
Page 1: CASE REPORTDennis H. Kraus, MD, Sec

Hypothyroidism caused by a nonvisible lingual thyroid

Create successful ePaper yourself

Delete template?

Save as template?