Examkin

Soru

Zorluk: KolayEndocrinology and Metabolism

Complaining of feeling constantly cold and sluggish, a 45-year-old woman presents to her primary care provider. She reports gaining 6 kg6 \text{ kg} (13.2 lbs13.2 \text{ lbs}) over the last six months without any dietary changes. On physical examination, her pulse is 56/min56/\text{min}, her skin is notably dry, and her deep tendon reflexes exhibit delayed relaxation. A comprehensive metabolic panel is within normal limits. Thyroid function testing demonstrates a free T4 concentration of 0.4 ng/dL0.4 \text{ ng/dL} (normal: 0.9–1.7 ng/dL0.9–1.7 \text{ ng/dL}) and a TSH concentration of 1.1 \muU/mL1.1 \text{ \mu U/mL} (normal: 0.5–5.0 \muU/mL0.5–5.0 \text{ \mu U/mL}). Which of the following is the most likely underlying cause of this patient's symptoms?

  1. Insufficient thyrotropin release from the anterior pituitary glandCevap
  2. B
    Lymphocytic infiltration and destruction of thyroid follicles
  3. C
    Altered peripheral conversion of thyroxine to triiodothyronine
  4. D
    Mutated thyroid hormone receptors causing target tissue resistance
  5. E
    Surreptitious use of unprescribed levothyroxine preparations

Cevap

Insufficient thyrotropin release from the anterior pituitary gland
This patient presents with classic clinical signs and symptoms of hypothyroidism, including fatigue, cold intolerance, weight gain, bradycardia, and delayed relaxation of deep tendon reflexes. Her laboratory results reveal a low free T4 level paired with a normal TSH level. In a normal physiologic state, a low free T4 would remove negative feedback on the anterior pituitary, resulting in a significantly elevated TSH level (primary hypothyroidism). The presence of a low free T4 with an inappropriately normal (or low) TSH indicates central (secondary) hypothyroidism, which is caused by insufficient thyrotropin (TSH) release from the anterior pituitary gland.

Adım Adım Çözüm

1
Interpret the patient's clinical presentation.
The patient exhibits bradycardia, weight gain, cold intolerance, dry skin, and delayed deep tendon reflexes, which strongly suggest a hypothyroid state.
Establishing the clinical state provides the context needed to correctly interpret the endocrine laboratory values.
2
Analyze the thyroid function laboratory tests.
The free T4 level is definitively low (0.4 ng/dL0.4 \text{ ng/dL}), confirming hypothyroidism. However, the TSH level is normal (1.1 \muU/mL1.1 \text{ \mu U/mL}).
The relationship between the primary hormone (T4) and the stimulating hormone (TSH) indicates where the defect lies in the endocrine axis.
3
Determine the pathophysiologic mechanism.
The absence of TSH elevation in the setting of low T4 indicates a failure of the pituitary gland to secrete thyrotropin, known as central or secondary hypothyroidism.
A healthy pituitary gland would sense the low free T4 and appropriately increase TSH secretion due to a lack of negative feedback.

Anahtar Kavram

Central (secondary) hypothyroidism is characterized by a low free T4 level accompanied by a TSH level that is inappropriately normal or low, indicating a failure of the anterior pituitary to secrete sufficient thyrotropin.
Tahmini Süre:50s
Bu soruyu puanla

Konular

Endocrinology and Metabolism

Bu konudan daha fazla soru