ThethyroidinGravesdiseaseischaracterizedbydiffusehypertrophyandhyperplasiaoffolliclesandlymphoidinfiltrates;glycosaminoglycandepositionandlymphoidinfiltratesareresponsiblefortheophthalmopathyanddermopathy.
LaboratoryfeaturesincludeelevationsinserumfreeT3andT4anddecreasedserumTSH.
Enlargement of the thyroid, or goiter, is the most common manifestation of thyroid disease. Diffuse and multinodular goiters are the result of impaired synthesis of thyroid hormone, most often caused by dietary iodine deficiency. Impairment of thyroid hormone synthesis leads to a compensatory rise in the serum TSH, which drives the hypertrophy and hyperplasia of thyroid follicular cells and, ultimately, enlargement of the thyroid gland. The degree of thyroid enlargement is proportional to the level and duration of thyroid hormone deficiency. These compensatory changes overcome the hormone deficiency and maintain a euthyroid metabolic state in the vast majority of affected individuals. However, if the underlying disorder is severe (e.g., a congenital biosynthetic defect), the compensatory responses may be inadequate, resulting in goitrous hypothyroidism.
Goiters can be endemic or sporadic.
• Endemic goiter occurs in geographic areas where the diet contains little iodine. The designation endemic is used when goiters are present in more than 10% of the population in a given region. Such conditions are particularly common in mountainous areas of the world, including the Himalayas and the Andes. With increased availability of dietary iodine supplementation, the frequency and severity of endemic goiter have declined significantly.
• Sporadic goiter occurs less frequently than endemic goiter. The condition is more common in females than in males, with a peak incidence in puberty or young adulthood, when there is an increased physiologic demand for T4. Sporadic goiter may be caused by several conditions, including the excessive ingestion of substances that interfere with thyroid hormone synthesis, such as calcium and vegetables belonging to the Brassicaceae (also called Cruciferae) family (e.g., cabbage, cauliflower, Brussels sprouts, turnips). In other instances goiter may result from inherited enzymatic defects that interfere with thyroid hormone synthesis (dyshormonogenetic goiter). In most cases, however, the cause of sporadic goiter is not apparent.
MORPHOLOGYEarlyinitsdevelopment,TSH-inducedhypertrophyandhyperplasiaofthyroidfollicularcellsusuallyresultindiffuse,symmetricenlargementofthegland(diffusegoiter).Thefolliclesarelinedbycrowdedcolumnarcells,whichmaypileupandformprojectionssimilartothoseseeninGravesdisease.Ifdietaryiodinesubsequentlyincreases,orifthedemandsforthyroidhormonedecrease,thefollicularepitheliuminvolutestoformanenlarged,colloid-richgland(colloidgoiter).Thecutsurfaceofthethyroidinsuchcasesusuallyisbrown,glassy-appearing,andtranslucent.Onmicroscopicexamination,thefollicularepitheliummaybehyperplasticintheearlystagesofdiseaseorflattenedandcuboidalduringperiodsofinvolution.Colloidisabundantduringthelatterperiods.
Withtime,recurrentepisodesofhyperplasiaandinvolutioncombinetoproduceamoreirregularenlargementofthethyroid,termedmultinodulargoiter.Virtuallyalllong-standingdiffusegoitersconvertintomultinodulargoiters.Multinodulargoitersaremultilobulate,asymmetricallyenlargedglandsthatmayattainamassivesize.Oncutsurface,irregularnodulescontainingvariableamountsofbrown,gelatinouscolloidareevident(