Each week, Osmosis shares a USMLE® Step 1-style practice question to test your knowledge of medical topics. Today’s case features a 38-year-old man with a fever and skin blistering after recent medication use. Can you determine the cause of his symptoms?
A 38-year-old man is brought to the emergency department to evaluate diffuse skin blistering. Around four days ago, the patient developed fevers, muscle aches, and malaise. He attributed the symptoms to a viral infection. This morning, he noticed multiple bullae on his skin all over his body. He has also experienced ulceration and desquamation of the lips and oropharynx, which has made it difficult for him to eat or drink. The patient has recently been prescribed trimethoprim-sulfamethoxazole for cellulitis and acetaminophen to treat an ankle sprain. He has been taking lamotrigine for seizure prevention for the past ten years. He received a tetanus booster shot one week ago. Temperature is 39.2°C (103°F), blood pressure is 153/82 mmHg, and pulse is 93/min. Physical examination reveals the following:
Painful lesions are present on over 5% of the patient’s skin. Which of the following factors most likely precipitated this patient’s current condition?
A. Tetanus booster vaccination
B. Trimethoprim-sulfamethoxazole use
C. Acetaminophen use
D. Recent upper respiratory tract infection
E. Lamotrigine use
Scroll down for the correct answer!
The correct answer to today’s USMLE® Step 1 Question is…
B. Trimethoprim-sulfamethoxazole use
Before we get to the Main Explanation, let’s look at the incorrect answer explanations. Skip to the bottom if you want to learn more about the correct answer right away!
Incorrect Answer Explanations
A. Tetanus booster vaccination
Vaccinations are a rare and highly debatable cause of Stevens-Johnsons syndrome (SJS)/toxic epidermal necrolysis (TEN). Instead, medications cause almost 90% of SJS/TEN cases in the United States.
C. Acetaminophen use
Acetaminophen is an unlikely cause of SJS/TEN and is not commonly implicated. Another component of this patient’s history places him at greater risk for developing SJS/TEN.
D. Recent upper respiratory tract infection
Patients with SJS/TEN may have a prodromal phase characterized by non-specific, flu-like symptoms such as fever, malaise, cough, and myalgias. However, viral infections are a rare and poorly documented cause of SJS/TEN.
E. Lamotrigine use
Lamotrigine is an anticonvulsant associated with around 9% of SJS/TEN cases. Most cases of SJS/TEN occur during the first eight weeks of therapy, making it unlikely for this patient, who has been taking it for many years. Additionally, antibiotics (e.g., trimethoprim-sulfamethoxazole, ꞵ-lactams) are more commonly implicated as the underlying cause of SJS/TEN.
Main Explanation
This patient presents with painful skin bullae and ulcerations, along with desquamation of mucosal surfaces. Given 5% of the patient’s skin is involved, his presentation is most consistent with Stevens-Johnsons syndrome (SJS). Of note, if skin involvement had exceeded 10%, the patient would have been diagnosed with toxic epidermal necrolysis (TEN).
SJS and TEN are characterized by painful vesicles/bullae on the skin, along with ulceration of mucosal membranes. SJS/TEN most often results from an adverse reaction to medications. Trimethoprim-sulfamethoxazole is most commonly implicated in SJS/TEN and is the underlying cause of around 26% of cases in the United States. Other medications that may trigger SJS/TEN include ꞵ-lactam antibiotics, anticonvulsants (e.g., lamotrigine, phenytoin), allopurinol, and NSAIDs.
Less commonly, SJS/TEN can arise after infection by pathogens such as Mycoplasma pneumoniae and herpes simplex virus.
Major Takeaway
Trimethoprim-sulfamethoxazole is the most common cause of Stevens-Johnson syndrome (SJS)/toxic epidermal necrolysis (TEN) in the United States. ꞵ-lactam antibiotics, anticonvulsants, allopurinol, and NSAIDs have also been identified as triggers. Less commonly, SJS/TEN can arise due to an infection.
References
- Micheletti, R.G., Chiesa-Fuxench, Z., Noe, M.H., et al. (2018) Steven-Johnson syndrome/toxic epidermal necrolysis: A multicenter retrospective study of 377 adult patients from the United States. The Journal of Investigative Dermatology. 138(11), 2315-2321. Doi: 10.1016/j.jid.2018.04.027.
- Oakley, A.M., Krishnamurthy, K. (2020) “Stevens-Johnson syndrome”. StatPearls [Internet]. Web Address: https://www.ncbi.nlm.nih.gov/books/NBK459323/.
Want to learn more about this topic?
Watch the Stevens-Johnson Syndrome video on Osmosis.
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