Drug-Induced Rashes in Skin of Color: Diagnostic Challenges

NEW YORK — Because of their heterogeneity in appearance, drug-induced skin rashes are a common diagnostic challenge, but eruptions in skin of color, particularly those with a delayed onset, require a high index of suspicion to speed the diagnosis.

This risk for a delayed or missed diagnosis in patients with darker skin is shared across skin rashes, but drug-induced hypersensitivity syndrome (DIHS) is a telling example, according to Joanna Harp, MD, director of the Inpatient Dermatology Consult Service, NewYork-Presbyterian Hospital, New York City.

DIHS, also known as a drug reaction with eosinophilia and systemic symptoms, is a type IV hypersensitivity reaction, Harp explained. While the fact that this disorder does not always include eosinophilia prompted the DHIS acronym, the maculopapular rash often serves as a critical clue of the underlying etiology.

In patients with darker skin, DIHS skin manifestations “can look different, can be more severe, and can have worse outcomes,” Harp said. As with other skin rashes that are primarily erythematous, the DIHS rash is often more subtle in Black-skinned patients, typically appearing gray or violaceous rather than red.

“The high amount of scale can be a clue,” said Harp, speaking at the 2024 Skin of Color Update. Scale is particularly prominent among Black patients, she said, because of the greater relative transepidermal water loss than lighter skin, increasing dryness and susceptibility to scale.

The maculopapular rash is “similar to a simple drug eruption, although it is usually more impressive,” she said. Emphasizing that DIHS is a systemic disease, she noted that the characteristic rash is typically accompanied by inflammation in multiple organs that not only includes the mucous membranes but can include major organs such as the lungs, kidneys, and heart.

In patients with DIHS and many of the even more serious types of rashes traced to drug exposures, such as Stevens-Johnson syndrome (SJS) or erythema multiforme, the delay to appearance of the rash from the time of exposure can be the most confusing element.

“It can be months for some drugs such as allopurinol,” said Harp, pointing out that Black and Asian patients are more likely to carry the HLA-B*5801 genotype, a known risk factor for allopurinol hypersensitivity.

Signs of AGEP Can Be Subtle in Black Patients

Some of the same principles for diagnosing drug-induced rash in darker skin can also be applied to acute generalized exanthematous pustulosis (AGEP), another type IV hypersensitivity reaction. Like all drug-induced rashes, the earlier AGEP is recognized and treated, the better the outcome, but in Black patients, the signs can be subtle.

“The onset is usually fast and occurs in 1-2 days after [the causative drug] exposure,” said Harp, adding that antibiotics, such as cephalosporins or penicillin, and calcium channel blockers are among the prominent causes of AGEP.

One of the hallmark signs of early-onset AGEP are tiny erythematous pustules in flexural areas, such as the neck or the armpits. The issue of detecting erythema in darker skin is also relevant to this area, but there is an additional problem, according to Harp. The pustules often dry up quickly, leaving a neutrophilic scale that further complicates the effort to see the characteristic erythema.

“If you see a lot of scale, look for erythema underneath. Think of inflammation,” Harp said, explaining that the clinical appearance evolves quickly. “If you do not see the pustules, it does not mean they were not there; you just missed them.”

In addition to the flexural areas, “AGEP loves the ears, the face, and the geographic tongue,” she said, offering several pearls to help with the diagnosis. These include side lighting to make papules easier to see, pressing on the skin to highlight the difference between erythematous skin and blanched skin, and checking less pigmented skin, such as on the hands and feet, which makes erythema easier to see.

Steroids are often the first-line treatment for drug-induced skin rashes, but Harp moves to etanercept or cyclosporine for the most serious drug reactions, such as SJS and toxic epidermal necrolysis.

Etanercept is typically her first choice because patients with systemic hypersensitivity reactions with major organ involvement are often quite ill, making cyclosporine harder to use. In her experience, etanercept has been well tolerated.

Conversely, she cautioned against the use of intravenous immunoglobulin (IVIG). Although this has been used traditionally for severe drug hypersensitivity reactions, “the data are not there,” she said. The data are stronger for a combination of high-dose steroids and IVIG, but she thinks even these data are inconsistent and not as strong as the data supporting etanercept or cyclosporine. She encouraged centers still using IVIG to consider alternatives.

After drug sensitivity reactions are controlled, follow-up care is particularly important for Black patients who face greater risks for sequelae, such as hypopigmentation, hyperpigmentation, or keloids. She recommended aggressive use of emollients and sunscreens for an extended period after lesions resolve to lessen these risks.

Differences in the manifestations of drug-induced skin rashes by race and ethnicity are important and perhaps underappreciated, agreed Shawn Kwatra, MD, professor and chairman of the Department of Dermatology, University of Maryland School of Medicine, Baltimore.

Asked to comment at the meeting, Kwatra said that he appreciated Harp’s effort to translate published data and her experience into an overview that increases awareness of the risk for missed or delayed diagnoses of drug-induced rashes in skin of color. He noted that the strategies to identify erythema and pustules, such as increased suspicion in skin of color and the extra steps to rule them out, such as the use of side lighting in the case of pustules for AGEP, are simple and practical.

Harp and Kwatra had no relevant disclosures.

Ted Bosworth is a medical journalist based in New York City.