Review of Answer Choices (Correct Answer in Green):
A. Drug eruption due to metoprolol
B. Flare of his pre-existing psoriasis
C. Atopic dermatitis
D. Drug eruption due to allopurinol
Explanation:
A. Drug eruption due to metoprolol. Drug reactions are a common cause of erythroderma. However, the skin rash typically occurs within weeks of starting the medication. Mr. Magoro has been taking metoprolol for approximately 5 years, so a new reaction to the medication at this time is unlikely.
B. Flare of his pre-existing psoriasis. Psoriasis is one of the most common causes of an erythrodermic skin rash. His past medical history for psoriasis makes a new flare more likely, especially if he had recently stopped potent steroids/methotrexate, was recently ill, or has recently been experiencing significant emotional stress. However, Mr. Magoro does not endorse any of these states, and the morphology of the skin rash shows no psoriatic features.
C. Atopic dermatitis. Atopic dermatitis is another common cause of erythroderma. Mr. Magoro has a family history of atopic dermatitis and asthma (2 factors of the “atopy triad”) in his father, though he denies any history of atopic dermatitis himself. Additionally, atopic dermatitis rarely develops in adults over 20 years old, and there are no morphological features of atopic dermatitis on skin exam.
D. Drug eruption due to allopurinol. This is the correct answer. Drug reactions are a common cause of erythroderma. Erythrodermic drug reactions typically occur within hours to weeks of starting a new medication. There are often morbilliform exanthem seen on the body, commonly on the anterior abdomen (as seen with our patient). Mr. Magoro started allopurinol 2 weeks ago, which fits with the drug eruption timeline. In addition, allopurinol is one of the most common causes of drug-induced erythroderma. Overall, this makes the new allopurinol prescription the most likely cause for his current skin condition.
