Thyroid

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Hyperthyroidism

 

Definition:

 

Hyperthyroidism refers to overactivity of the thyroid gland leading to excessive synthesis of thyroid hormones and accelerated metabolism in the peripheral tissues. Thyrotoxicosis, on the other hand, refers to the clinical effects of an unbound thyroid hormone, whether or not the thyroid gland is the primary source.

 

The elevated level of thyroid hormones can result in clinical manifestations ranging from mild to severely toxic with resultant morbidity and mortality for affected patients.

 

Causes:

 

The major causes of hyperthyroidism in humans are:

High blood levels of thyroid hormones (most accurately termed hyperthyroxinemia) can occur for a number of other reasons:

Inflammation of the thyroid is called thyroiditis. There are a number of different kinds of thyroiditis including Hashimoto's (immune mediated), subacute (inflammatory), and DeQuervain's (granulomatous). These may be initially associated with secretion of excess thyroid hormone, but often progress to gland dysfunction and thus, an eventual hormone deficiency.

Struma ovarii (a teratoma of the ovary) can produce excess thyroid hormone.

Consumption of excess thyroid hormone tablets is possible, as is the now rare event of consumption of ground beef contaminated with thyroid tissue, and thus thyroid hormone (termed "hamburger hyperthyroidism").

Amiodarone, a heart medication, can sometimes cause hyperthyroidism by a variety of different mechanisms.

Postpartum thyroiditis occurs in about 7% of women during the year after they give birth. PPT typically has several phases, the first of which is hyperthyroidism. Many times, the hyperthyroidism corrects itself within weeks or months without any treatment necessary.

Signs and symptoms:

  • Weight loss: Patients typically report an average loss of approximately 15% of their prior weight.
  • Palpitations
  • Chest pain - Often occurs in the absence of cardiovascular disease
  • Psychosis
  • Menstrual irregularity
  • Disorientation
  • Tremor
  • Nervousness, anxiety, or emotional lability
  • Heat intolerance
  • Increased perspiration
  • Fatigue
  • Weakness - Typically affects proximal muscle groups
  • Edema
  • Dyspnea
  • Frequent bowel movements
  • Fever
  • Tachycardia (often out of proportion to the fever)
  • Diaphoresis (often profuse)
  • Dehydration secondary to GI losses and diaphoresis
  • Warm, moist skin
  • Widened pulse pressure
  • Congestive heart failure (may be a high output failure)
  • Thyromegaly
  • Exophthalmos
  • Shock
  • Atrial fibrillation
  • Typically in elderly patients
  • May be refractory to attempted rate control with digitalis
  • Converts after antithyroid therapy in 20-50% of patients
  • Myopathy
  • Thyroid bruit - Relatively specific for thyrotoxicosis
  • Fine, resting tremor
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