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Soru

Zorluk: KolayGeneral Internal Medicine

A 4141-year-old woman comes to the clinic for evaluation of worsening fatigue, generalized weakness, and a 33-kg weight gain over the past 55 months. She also reports increased sensitivity to cold and irregular menstrual cycles. She takes no daily medications. Her blood pressure is 110/70110/70 mm Hg, and her pulse is 5858/min. Physical examination reveals dry skin and delayed relaxation of the deep tendon reflexes. Laboratory testing shows a thyroid-stimulating hormone (TSH) level of 0.15 μU/mL0.15 \ \mu\text{U/mL} (normal: 0.4−4.0 μU/mL0.4-4.0 \ \mu\text{U/mL}) and a free thyroxine (T4) level of 0.6 ng/dL0.6 \text{ ng/dL} (normal: 0.9−1.7 ng/dL0.9-1.7 \text{ ng/dL}). Which of the following is the most likely diagnosis?

  1. Central hypothyroidismCevap
  2. B
    Primary hypothyroidism
  3. C
    Subclinical hypothyroidism
  4. D
    Graves disease
  5. E
    Euthyroid sick syndrome

Cevap

Central hypothyroidism
The patient presents with classic clinical symptoms of hypothyroidism, including fatigue, weight gain, cold intolerance, bradycardia, and delayed relaxation of deep tendon reflexes. The laboratory findings show a low free T4 level, confirming a hypothyroid state. In a normally functioning hypothalamic-pituitary-thyroid axis, a low free T4 should stimulate the pituitary gland to increase TSH production. However, this patient's TSH is inappropriately low rather than elevated. The combination of low free T4 and low TSH indicates central (secondary) hypothyroidism, which is caused by a failure of the pituitary gland or hypothalamus to produce sufficient stimulating hormones.

Adım Adım Çözüm

1
Evaluate the patient's clinical presentation and physical examination findings.
The presence of fatigue, weight gain, cold intolerance, bradycardia, and delayed relaxation of deep tendon reflexes indicates a clinical state of hypothyroidism.
To establish the primary clinical syndrome prior to interpreting the laboratory values.
2
Interpret the free T4 laboratory value.
The free T4 level is low at 0.6 ng/dL0.6 \text{ ng/dL}, which biochemically confirms the hypothyroid state.
To verify the clinical suspicion of hypothyroidism with objective data.
3
Assess the TSH level to determine the etiology of the hypothyroidism.
The TSH is low (0.15 μU/mL0.15 \ \mu\text{U/mL}) instead of being elevated, indicating a failure of the hypothalamic-pituitary axis to respond to the low free T4.
To differentiate between primary (thyroid gland failure) and central (pituitary/hypothalamic failure) causes of hypothyroidism.

Anahtar Kavram

The diagnosis of central hypothyroidism requires the identification of a low free T4 level accompanied by a low or inappropriately normal TSH level, indicating a lack of appropriate pituitary stimulation.
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General Internal Medicine

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