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Zorluk: OrtaHematology and Oncology

A 58-year-old woman presents to the clinic complaining of progressive fatigue, generalized weakness, and a tingling sensation in her lower extremities that has steadily worsened over the past four months. Her past medical history is significant for vitiligo and Hashimoto thyroiditis, for which she takes daily levothyroxine. Vital signs are temperature 36.8°C (98.2°F), blood pressure 118/76 mmHg, heart rate 82/min, and respiratory rate 14/min. Physical examination reveals pale conjunctivae, a smooth and beefy-red tongue, and decreased vibratory sensation in both feet.

Laboratory results are as follows:

TestResultReference Range
Hemoglobin8.4 g/dL12.0 - 15.5 g/dL
Mean corpuscular volume (MCV)116 fL80 - 100 fL
Leukocytes3,500/mcL4,500 - 11,000/mcL
Platelets120,000/mcL150,000 - 400,000/mcL
Serum vitamin B12245 pg/mL200 - 900 pg/mL
Serum folate14 ng/mL2 - 20 ng/mL
Thyroid-stimulating hormone (TSH)2.2 µU/mL0.4 - 4.0 µU/mL
Free T41.3 ng/dL0.9 - 2.4 ng/dL

A peripheral blood smear demonstrates macro-ovalocytes and several neutrophils with six or more lobes.

Which of the following is the most appropriate next step in management?

  1. A
    Increase the daily dose of levothyroxine
  2. B
    Initiation of oral folic acid supplementation
  3. Measurement of serum methylmalonic acid levelCevap
  4. D
    Bone marrow aspiration and biopsy
  5. E
    Transthoracic echocardiography

Cevap

The most appropriate next step is to measure the serum methylmalonic acid level to confirm a functional vitamin B12 deficiency.
The correct answer is measurement of serum methylmalonic acid. This patient has megaloblastic anemia (macrocytosis, hypersegmented neutrophils, pancytopenia) and neurologic symptoms (loss of vibratory sensation, paresthesias). These findings strongly suggest vitamin B12 deficiency, which is commonly associated with other autoimmune diseases like her vitiligo and Hashimoto thyroiditis (suggesting an underlying pernicious anemia). Her serum vitamin B12 level is borderline (200-300 pg/mL). In such cases, measuring serum methylmalonic acid (MMA) is required to confirm the diagnosis, as MMA will be uniquely elevated due to the lack of B12 cofactor activity.

Adım Adım Çözüm

1
Analyze the patient's clinical presentation.
The patient exhibits progressive fatigue, lower extremity paresthesias, decreased vibratory sensation, and a beefy-red tongue (glossitis).
Identifying the constellation of symptoms points toward subacute combined degeneration and glossitis, which are classic manifestations of vitamin B12 deficiency.
2
Evaluate the laboratory results and peripheral blood smear.
Pancytopenia (low hemoglobin, leukocytes, platelets) with an elevated MCV (116 fL) and hypersegmented neutrophils indicate a megaloblastic anemia.
This narrows the differential diagnosis to vitamin B12 deficiency, folate deficiency, or medications that interfere with DNA synthesis.
3
Interpret the specific vitamin levels from the panel.
The serum folate level is normal (14 ng/mL), but the serum vitamin B12 level is borderline (245 pg/mL).
A B12 level between 200 and 300 pg/mL is equivocal and requires further confirmatory testing before initiating lifelong therapy.
4
Determine the appropriate confirmatory test.
Measurement of serum methylmalonic acid (MMA) is indicated.
MMA is elevated in true B12 deficiency because vitamin B12 is a required cofactor for the conversion of methylmalonyl-CoA to succinyl-CoA. Elevated MMA confirms the diagnosis when serum B12 levels are borderline.

Anahtar Kavram

In patients with clinical signs of megaloblastic anemia and borderline serum vitamin B12 levels (200-300 pg/mL), measurement of serum methylmalonic acid (MMA) is the most appropriate next step to confirm the diagnosis.
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