Examkin

Soru

Zorluk: KolayGeneral Internal Medicine

A 38-year-old woman comes to the clinic due to a 3-month history of worsening fatigue, generalized weakness, and a 4.5-kg (10-lb) weight gain despite a decreased appetite. She also reports feeling constantly cold and having increasingly irregular menstrual cycles. Her temperature is 36.1°C (97.0°F), blood pressure is 100/65 mm Hg, and pulse is 54/min. Physical examination shows dry skin and delayed relaxation of the deep tendon reflexes. Laboratory studies show a thyroid-stimulating hormone (TSH) level of 0.1 μ\mu U/mL (normal: 0.5-5.0 μ\mu U/mL) and a free thyroxine (T4) level of 0.4 ng/dL (normal: 0.9-1.7 ng/dL). Which of the following is the most likely cause of this patient's findings?

  1. A
    Autoimmune destruction of the thyroid gland
  2. B
    Thyroid-stimulating immunoglobulin production
  3. Compression of pituitary thyrotrophsCevap
  4. D
    Exogenous levothyroxine consumption
  5. E
    Decreased peripheral conversion of T4 to T3

Cevap

Compression of pituitary thyrotrophs, leading to central (secondary) hypothyroidism.
The correct answer identifies the etiology of central hypothyroidism. This patient has classic hypothyroid symptoms (fatigue, cold intolerance, weight gain, bradycardia), which correlates with her low free T4 level. However, her TSH is inappropriately suppressed rather than elevated. This lack of appropriate pituitary response indicates a central cause of hypothyroidism, most commonly resulting from a pituitary macroadenoma that causes mass effect and compression of normal thyrotrophs.

Adım Adım Çözüm

1
Analyze the patient's symptoms and vital signs.
The patient presents with fatigue, weight gain, cold intolerance, bradycardia, and delayed deep tendon reflexes.
Identifying the clinical syndrome is the first step; these findings strongly suggest a hypothyroid state.
2
Interpret the thyroid function tests.
The free T4 is abnormally low, confirming hypothyroidism. The TSH is also abnormally low.
Normally, a low T4 should trigger an elevated TSH via negative feedback. An inappropriately low TSH in the setting of low T4 localizes the defect to the anterior pituitary or hypothalamus.
3
Determine the most likely etiology for the laboratory pattern.
The pattern indicates central hypothyroidism, which is most often caused by a pituitary mass.
A nonfunctioning pituitary adenoma can compress normal pituitary thyrotrophs, leading to decreased TSH production and subsequent hypothyroidism. This also commonly causes menstrual irregularities via compression of gonadotrophs or hyperprolactinemia due to stalk compression.

Anahtar Kavram

Central (secondary) hypothyroidism is characterized by clinical signs of hypothyroidism combined with a low free T4 and an inappropriately normal or low TSH.
Bu soruyu puanla

Konular

General Internal Medicine

Bu konudan daha fazla soru