06/12/2022
Differential Diagnosis of Exanthematous Drug Eruptions
Cutaneous adverse drug reactions are undesirable changes in the structure or function of the skin, appendages, or mucous membranes resulting from the use of medications at normally recommended doses. Drug eruptions are common, affecting approximately 2% to 3% of hospitalized patients.1, 2, 3 The morphology of these eruptions may be exanthematous, urticarial, papulosquamous, pustular, vesiculobullous, or granulomatous. In addition, the eruptions may sometimes present with annular, polycyclic, or polymorphous configurations.
The clinical presentations of drug eruptions are highly variable. Most drug eruptions are mild, self-limited, and usually resolve after the offending agent has been discontinued; however, approximately 1 in 1,000 hospitalized patients may have severe cutaneous adverse reactions (SCARs), which are potentially lethal adverse drug reactions that involve the skin and mucous membranes and may also damage internal organs.4 Prompt recognition of the alarming signs of SCARs and providing adequate treatment for them may thus be life-saving.
When a patient has a new-onset widespread eruption (exanthem), an accurate history and a high index of suspicion regarding the possibility of an offending drug is vital for making a correct diagnosis. A thorough history taking should be performed, with the following questions and steps being asked and taken:
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When did the onset of the eruption occur? Establishing a chronologic relationship between drug exposure and the onset of the eruption is helpful for the identification of the culprit drug.
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What are the sign and symptoms of the eruption? Or is it asymptomatic? Is it itchy or painful?
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Are there systemic symptoms and signs (eg, fever, fatigue, sore throat)?
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A detailed drug history, including all prescribed and nonprescribed medications (eg, over-the-counter tablets, herbal medications, or topical preparations) taken within the last month, should be obtained.
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What medications is the patient taking, and for what is each medication? Ask to actually see the medications or a list of the patient's prescriptions to be sure of the type or types of medications being taken (eg, some patients may take oral anticonvulsants due to chronic neuralgia and may erroneously describe these medications as “analgesics” or “painkillers”).
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How long has the patient been taking each medication, and how often does the patient take it?
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Does the patient have any known drug allergies? If so, what was the allergic reaction? Many patients mistakenly consider their previous nonallergic adverse drug reactions (eg, nausea, vomiting, diarrhea) to be the result of a “drug allergy.”
It is very important to know that common exanthematous drug reactions can occur as late as 2 weeks after a medication has been discontinued.5 The time between the culprit drug exposure and the onset of a SCAR may be even longer. For example, Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) often begin between 4 and 28 days after the culprit drug administration.6 Drug reaction with eosinophilia and systemic symptoms (DRESS) usually has an even longer latency period, developing between 3 and 8 weeks after the drug exposure.
https://www.sciencedirect.com/science/article/abs/pii/S0738081X21002662
