What laboratory study is most likely to identify the cause of a 32-year-old man's symptoms of fatigue and near-syncope, with a history of anxiety treated with propranolol (propranolol), a blood pressure of normotension, and bradycardia, and an electrocardiogram (ECG) showing abnormal findings?

From the Guidelines

The most likely laboratory study to identify the cause of this patient's symptoms is a thyroid-stimulating hormone (TSH) level. This 32-year-old man presents with fatigue, near-syncope, bradycardia (heart rate of 40/min), and an ECG that likely shows changes consistent with hypothyroidism. The combination of profound bradycardia, fatigue, and pale appearance strongly suggests hypothyroidism, which can develop following a viral illness like his recent head cold. Hypothyroidism can cause sinus bradycardia and other ECG changes including low voltage, T-wave flattening, and prolonged QT interval. The patient's symptoms of fatigue and near-syncope are likely related to his bradycardia, which is a common cardiovascular manifestation of hypothyroidism. Additionally, propranolol use in a patient with undiagnosed hypothyroidism could worsen bradycardia, as beta-blockers can mask symptoms of hyperthyroidism or exacerbate bradycardia in hypothyroidism. Measuring TSH would be the most appropriate first step to confirm or rule out thyroid dysfunction as the underlying cause of his presentation, as recommended by recent guidelines 1.

Some key points to consider in this case include:

• The patient's symptoms and physical examination findings are consistent with hypothyroidism, which can cause bradycardia and other ECG changes.
• The patient's recent viral illness could be a trigger for the development of hypothyroidism.
• Propranolol use could exacerbate bradycardia in hypothyroidism, making it important to rule out thyroid dysfunction.
• Measuring TSH is a simple and non-invasive test that can help confirm or rule out thyroid dysfunction as the underlying cause of the patient's symptoms.

Overall, measuring TSH is the most appropriate first step in evaluating this patient's symptoms, given the combination of clinical findings and potential risks associated with propranolol use in hypothyroidism, as supported by recent guidelines 1.

From the Research

Patient Presentation and History

The patient is a 32-year-old man presenting with a 2-week history of fatigue and near-syncope. He has a past medical history of anxiety, for which he uses propranolol, and works as a painter. His vital signs show a blood pressure of 110/68 mmHg and a heart rate of 40/min.

Possible Causes and Relevant Laboratory Studies

Given the patient's occupation as a painter, lead exposure is a potential cause of his symptoms. The studies 2, 3, 4, 5, 6 discuss lead toxicity and its treatment.

• Lead toxicity can cause a range of symptoms, including fatigue, neuropsychiatric symptoms, and renal insufficiency.
• The patient's symptoms and occupation suggest that lead exposure could be a possible cause.
• Laboratory studies that could identify the cause of the patient's symptoms include:
  • Complete blood count (CBC) to rule out anemia, which can cause fatigue
  • Basic metabolic profile to assess renal function and electrolyte levels
  • Lead level to assess for lead toxicity
  • Other studies such as antinuclear antibody test, dark-field microscopy, Lyme titer, and thyroid-stimulating hormone level may not be directly relevant to the patient's symptoms and occupation.

Most Likely Laboratory Study

Based on the patient's occupation and symptoms, the most likely laboratory study to identify the cause of his symptoms is:

• E. lead level This is because lead exposure is a known risk for painters, and lead toxicity can cause a range of symptoms, including fatigue and near-syncope, as seen in this patient 2, 3, 4, 5, 6.