Examkin

Soru

Zorluk: OrtaFormulating a Differential Diagnosis

A 62-year-old man comes to the outpatient clinic for a follow-up evaluation. Over the past 4 months, he has experienced progressive fatigue, muscle weakness, and worsening constipation. He also reports an unintentional weight loss of 5 kg (11 lb) during this time. His medical history is significant for hypertension and a 35-pack-year smoking history, although he quit smoking 2 years ago. His only medication is hydrochlorothiazide. Vital signs are within normal limits. Physical examination reveals no palpable cervical, supraclavicular, or axillary lymphadenopathy. Cardiopulmonary and abdominal examinations are unremarkable.

Laboratory studies reveal the following:

TestResultReference Range
Calcium, serum11.8 mg/dL8.4-10.2 mg/dL
Phosphorus, serum3.8 mg/dL2.5-4.5 mg/dL
Blood urea nitrogen22 mg/dL8-20 mg/dL
Creatinine, serum1.1 mg/dL0.7-1.3 mg/dL
Intact parathyroid hormone9 pg/mL15-65 pg/mL
25-hydroxyvitamin D32 ng/mL20-50 ng/mL
1,25-dihydroxyvitamin D94 pg/mL18-72 pg/mL

A chest radiograph demonstrates bilateral hilar lymphadenopathy without focal pulmonary consolidations. Based on the clinical presentation and laboratory findings, which of the following is the most likely diagnosis?

  1. SarcoidosisCevap
  2. B
    Squamous cell carcinoma of the lung
  3. C
    Multiple myeloma
  4. D
    Primary hyperparathyroidism
  5. E
    Thiazide-induced hypercalcemia

Cevap

Sarcoidosis
The correct answer is Sarcoidosis. This patient presents with symptomatic hypercalcemia, a suppressed parathyroid hormone (PTH) level, and an elevated 1,25-dihydroxyvitamin D level. The diagnostic approach to hypercalcemia requires analyzing the PTH level first. A suppressed PTH (<20 pg/mL) confirms PTH-independent hypercalcemia. The subsequent step is to evaluate PTH-related peptide (PTHrP) and vitamin D metabolites. This patient's elevated 1,25-dihydroxyvitamin D indicates increased extrarenal 1-alpha-hydroxylase activity, an enzyme that converts 25-hydroxyvitamin D to its active form. This ectopic enzyme activity is a hallmark of granulomatous diseases (most commonly sarcoidosis) due to expression by activated macrophages. It can also be seen in certain lymphomas. The patient's chest radiograph showing bilateral hilar lymphadenopathy further solidifies the clinical picture of sarcoidosis. The systemic symptoms, including fatigue and weight loss, are also frequently observed in this inflammatory condition.

Adım Adım Çözüm

1
Analyze the patient's laboratory results to identify the physiological mechanism of hypercalcemia.
The hypercalcemia is accompanied by a suppressed parathyroid hormone (PTH) level and an elevated 1,25-dihydroxyvitamin D level.
Determining whether hypercalcemia is PTH-dependent or independent, and evaluating the vitamin D axis, is the critical first step in narrowing the differential diagnosis.
2
Correlate the identified hypercalcemia mechanism with the patient's clinical and radiographic findings.
The combination of 1,25-dihydroxyvitamin D-mediated hypercalcemia and bilateral hilar lymphadenopathy points to a granulomatous disease.
Granulomatous diseases exhibit ectopic 1-alpha-hydroxylase activity in macrophages, which converts 25-hydroxyvitamin D to its active form, leading to hypercalcemia that is independent of PTH.

Anahtar Kavram

Formulating a differential diagnosis for hypercalcemia by utilizing parathyroid hormone and vitamin D metabolite levels, specifically recognizing 1,25-dihydroxyvitamin D-mediated hypercalcemia in granulomatous diseases like sarcoidosis.
Tahmini Süre:1m 30s
Bu soruyu puanla

Konular

Formulating a Differential Diagnosis

Bu konudan daha fazla soru