A 30-year-old female with Graves’ disease was started on propylthiouracil (PTU) one month ago. She now presents with complaints of a sore throat, low-grade fever, and feeling generally unwell. Given her recent initiation of antithyroid medication, which of the following tests should be performed as the initial step in evaluating her condition?
A. Complete Blood Count (CBC)
B. Blood culture
C. Serum TSH
D. Serum T3 by RIA
E. Antithyroid antibodies
Correct Answer: A. Complete Blood Count (CBC)
Explanation:
The most likely cause of this patient’s symptoms—sore throat, low-grade fever, and general malaise—is agranulocytosis, a potentially serious side effect of propylthiouracil (PTU). Agranulocytosis is characterized by a severe decrease in white blood cells, particularly neutrophils, leading to an increased susceptibility to infections and other symptoms such as fever and sore throat. It is a well-known complication of PTU therapy, especially within the first 3 months of treatment.
In this context, the initial diagnostic test should be a Complete Blood Count (CBC), which will help assess the patient’s white blood cell count. Specifically, you are looking for neutropenia or agranulocytosis, which can explain her acute symptoms. Early recognition of agranulocytosis allows for prompt discontinuation of PTU and initiation of appropriate management.
Why Other Options Are Incorrect:
B. Blood culture:
- While blood cultures may be important if the patient is suspected of having a bacterial infection, the symptoms of fever and sore throat in the context of recent PTU use point more toward drug-induced agranulocytosis rather than an infection. The CBC is the first test that should be performed to evaluate for agranulocytosis.
C. Serum TSH:
- Serum TSH (Thyroid Stimulating Hormone) levels are used for evaluating thyroid function, especially in patients with Graves’ disease, but they are not the primary concern when a patient presents with symptoms that suggest hematologic complications (such as agranulocytosis). Thyroid function should be assessed after the patient’s acute issue is addressed.
D. Serum T3 by RIA:
- Serum T3 (triiodothyronine) levels would be useful for evaluating thyroid hormone levels, but in this case, the patient’s symptoms are more likely due to agranulocytosis caused by PTU therapy. A Complete Blood Count should be prioritized to check for leukopenia or neutropenia, rather than focusing on thyroid hormone levels at this time.
E. Antithyroid antibodies:
- Antithyroid antibodies (such as TRAB or TSH receptor antibodies) are used for diagnosing Graves’ disease. However, this patient already has a known diagnosis of Graves’ disease, so testing for antibodies is not necessary for evaluating her current symptoms. The concern here is agranulocytosis due to PTU, and a CBC is the appropriate test.
Clinical Features of Agranulocytosis Due to PTU:
- Symptoms:
- Common presenting symptoms include sore throat, fever, malaise, and generalized weakness. These occur due to the neutropenia or agranulocytosis that impairs the immune system’s ability to fight infections.
- Risk Period:
- Agranulocytosis typically develops within the first 3 months of starting PTU therapy. Although it can occur later, early detection is critical.
- Physical Exam Findings:
- Patients may exhibit oral ulcers, pharyngitis (sore throat), and other signs of infection due to a low white blood cell count. The CBC will provide the necessary information on the severity of neutropenia.
Management of Agranulocytosis Due to PTU:
- Discontinuation of PTU:
- The first step in management is to discontinue PTU immediately. Agranulocytosis is dose-independent, meaning that even small doses of PTU can cause this severe side effect. Methimazole can be used as an alternative antithyroid drug, as it has a lower risk of causing agranulocytosis.
- Granulocyte Colony-Stimulating Factor (G-CSF):
- In severe cases, G-CSF may be administered to stimulate the production of white blood cells and help the body recover from neutropenia.
- Antibiotics:
- If infection is suspected, broad-spectrum antibiotics should be started immediately while awaiting culture results. This is important if the patient has an ongoing fever or signs of infection due to the low white blood cell count.
Conclusion:
This patient’s symptoms of sore throat, fever, and malaise, occurring after the initiation of propylthiouracil therapy for Graves’ disease, raise suspicion for agranulocytosis. The initial test of choice is a Complete Blood Count (CBC), which will confirm whether the patient has neutropenia or agranulocytosis. Prompt recognition of this side effect is essential to prevent further complications, and management involves discontinuing PTU, monitoring the CBC, and potentially using treatments like G-CSF and antibiotics. Early intervention is crucial for patient safety and optimal care.