Not Associated with Hyperthyroidism

Subacute granulomatous thyroiditis (painful)

Subacute lymphocytic thyroiditis (painless)

Struma ovarii (ovarian teratoma with ectopic thyroid)

Factitious thyrotoxicosis (exogenous thyroxine intake)

*Associated with increased TSH; all other causes of thyrotoxicosis associated with decreased TSH.

one (albeit the most common) cause of thyrotoxicosis. The terms primary and secondary hyperthyroidism are sometimes used to designate hyperthyroidism arising from an intrinsic

thyroid abnormality and that arising from processes outside of the thyroid, such as a TSH-secreting pituitary tumor. With this disclaimer, we will follow the common practice of using

the terms thyrotoxicosis and hyperthyroidism interchangeably. The three most common causes of thyrotoxicosis are also associated with hyperfunction of the gland and include the

following:

• Diffuse hyperplasia of the thyroid associated with Graves disease (accounts for 85% of cases)

• Hyperfunctional multinodular goiter

• Hyperfunctional adenoma of the thyroid

Clinical Course.

The clinical manifestations of hyperthyroidism are protean and include changes referable to the hypermetabolic state induced by excess thyroid hormone as well as those related to

overactivity of the sympathetic nervous system (i.e., an increase in the b-adrenergic "tone").

Excessive levels of thyroid hormone result in an increase in the basal metabolic rate. The skin of thyrotoxic patients tends to be soft, warm, and flushed because of increased blood flow

and peripheral vasodilation to increase heat loss. Heat intolerance is common. Sweating is increased because of higher levels of calorigenesis. Increased basal metabolic rate also results

in characteristic weight loss despite increased appetite.

Cardiac manifestations are among the earliest and most consistent features of hyperthyroidism. Patients with hyperthyroidism can have an increase in cardiac output, owing to both

increased cardiac contractility and increased peripheral oxygen requirements. Tachycardia, palpitations, and cardiomegaly are common. Arrhythmias, particularly atrial fibrillation, occur

frequently and are more common in older patients. Congestive heart failure may develop, particularly in elderly patients with pre-existing cardiac disease. Myocardial changes, such as

foci of lymphocytic and eosinophilic infiltration, mild fibrosis in the interstitium, fatty changes in myofibers, and an increase in size and number of mitochondria, have been described.

Some patients with thyrotoxicosis develop a reversible diastolic dysfunction and a "low-output" failure, so-called thyrotoxic dilated cardiomyopathy.

In the neuromuscular system, overactivity of the sympathetic nervous system produces tremor, hyperactivity, emotional lability, anxiety, inability to concentrate, and insomnia. Proximal

muscle weakness is common with decreased muscle mass (thyroid myopathy).

Ocular changes often call attention to hyperthyroidism. A wide, staring gaze and lid lag are present because of sympathetic overstimulation of the levator palpebrae superioris ( Fig. 24-

8 ). However, true thyroid ophthalmopathy associated with proptosis is a feature seen only in Graves disease (see below).

In the gastrointestinal system, sympathetic hyperstimulation of the gut results in hypermotility, malabsorption, and diarrhea.

The skeletal system is also affected in hyperthyroidism. Thyroid hormone stimulates bone resorption, resulting in increased porosity of cortical bone and reduced volume of trabecular

bone. The net effect is osteoporosis and an increased risk of fractures in patients with chronic hyperthyroidism.

Date: 2016-04-22; view: 619