63

63 CASE 63


A 30-year-old woman visits her primary care doctor with concerns about a growth on her neck.


The patient also complains about anxiety and irritability. She has noticed a 6-pound loss of weight over the past 2 months despite an increase in her appetite. She also feels uncomfortable when in a warm room.



PHYSICAL EXAMINATION



VS: T 38°C, P 110/min, R 18/min, BP 140/90 mm Hg, BMI 26

PE: Thyroid gland is enlarged symmetrically. Skin is warm and moist to the touch. Exophthalmos is evident by her protruding eyes. Onycholysis is present in her nails.


LABORATORY STUDIES



Blood analysis (thyroid panel):
• Serum TSH: 0.1 mIU/mL (normal: 0.4-6.0 mIU/mL)

• Thyroxine: 40 μg/dL (normal: 4.5-11.2 μg/dL)

• Triiodothyronine: 280 ng/dL (normal: 95-190 ng/dL)

• TSH receptor antibody: positive (normal: negative)


DIAGNOSIS


Graves’ disease



PATHOPHYSIOLOGY OF KEY SYMPTOMS


The patient’s major complaints—hyperactivity, weight loss, and warm intolerance—are all characteristic of an elevated metabolic rate. The enlargement of the thyroid gland and the exophthalmos are consistent with an elevation of thyroid hormone mediating the disturbances. Plasma analysis showing an elevated T3 and T4 confirm her hyperthyroid status.


Thyroid hormone is an iodinated derivative of the amino acid tyrosine. Thyroid hormone synthesis is controlled by peptides released from the hypothalamus and the anterior pituitary. The hypothalamus releases thyrotropin-releasing hormone (TRH), which acts on the anterior pituitary to release thyroid stimulating hormone (TSH). TSH binds to receptors on the follicle cells of the thyroid gland to stimulate iodide uptake and thyroid hormone synthesis. Mature thyroid hormone has either three iodides (T3) or four iodides (T4) attached to the tyrosine. The majority of thyroid hormone released by the thyroid gland is T4, but T3 has a stronger biologic activity. The combination of T3 and T4 together is referred to as thyroid hormone (Fig. 63-1).


image

FIGURE 63–1 Free T3 and T4 provide feedback control for pituitary thyroid-stimulating hormone (TSH) release. Most circulating thyroid hormone is bound to thyroid-binding globulin. Free thyroid hormone levels produce both the biologic effects and the negative feedback signal regulating TSH release. TRH, thyroid-releasing hormone.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 63

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