Endocrine physiology

Presentation: History and physical examination

J.B is a 38 year old woman who presents to her primary care physician with a chief complaint of fatigue and weight gain. She was in her normal state of health until about 6 months ago. Since that time, she has been getting tired more easily and has lost over 12 pounds despite no significant change in her workout regime. In fact, she notes that her appetite has actually increased. Additionally, she reports diarrhea occurring 1 to 2 times per week. She has also found more hair than usual in her hairbrush. She diligently takes her medications as prescribed, exercises 3 times per week, and attempts to eat healthy. She does admit to occasional alcohol intake during the weekends.

On physical examination, J.B. appears anxious and has difficulty remaining still on the examination table. Her vital signs are notable for a blood pressure of 165/76 mm Hg, heart rate of 111 beats per minute, temperature 37.6° C, and a respiratory rate of 14 breaths per minute. When asked to extend her arms, she has a noticeable fine tremor of the extremities. On HEENT (head, eyes, ears nose, throat) examination, she has a slight bulging of her eyes, and her thyroid gland is enlarged and smooth. Her skin feels warm and moist. Her neurologic examination is notable for brisk reflexes. She is alert and oriented.

Discussion

The review of systems and physical examination has revealed that J.B likely is suffering from hyperthyroidism.

The leading cause of hyperthyroidism is Graves disease, a condition that more commonly affects young woman. Graves disease is caused by a type of immunoglobulin (Ig)G known as thyroid-stimulating antibodies (TSAb). These antibodies bind to the thyroid stimulating hormone (TSH) receptor on the follicular cells of the thyroid. This stimulates the thyroid to generate significant amounts of thyroid hormone (T ₃ and T ₄ ) while the negative feedback loop of the hypothalamus-pituitary-thyroid axis is inhibited.

Hyperthyroidism can also be caused by a toxic adenoma or by multiple hyperfunctioning nodules. Thyrotoxicosis factitia is seen with ingestion of excessive thyroid hormone, and struma ovarii is seen when an ovarian teratoma has hyperactive thyroid tissue. However, these causes of hyperthyroidism are more rare.

A normally functioning thyroid gland has two hormone-producing cell types. As discussed in Chapter 30 , the follicular cells are responsible for producing, storing and releasing triiodothyronine (T ₃ ) and thyroxine (T ₄ ), whereas the parafollicular cells secrete calcitonin. T ₄ is the major circulating form within the body, however T ₃ is the active form of thyroid hormone inside cells. When increased levels of T ₃ and T _4. are secreted, multiple effects are seen throughout the body. Many of these can be identified with a thorough review of systems and physical exam, even in the absence of a laboratory evaluation ( Box 36.1.1 ).