PD-1 Inhibitors As a Trigger
Chronic pruritus caused by the anticancer PD-1 inhibitors is becoming more common as the utilization of these immune checkpoint inhibitors increases, Dr. Kwatra noted. “You don’t see much in the skin, but [these patients have] very high IgE and eosinophils,” he said. “We’ve been seeing more reports recently of utilizing agents that target type 2 inflammation off label for PD-1 inhibitor–related skin manifestations.”
One such patient with PD-1 inhibitor–induced pruritus was a 65-year-old White man with metastatic melanoma who reported a 6-month history of itching that began 3 weeks after the start of treatment with the PD-1 inhibitor pembrolizumab. His WI-NRS score was 10 despite treatment with topical steroids and antihistamines. He had a history of psoriasis. Labs showed elevated IgE (1350 kU/L) and eosinophil levels (4.5%). At a 4-month follow-up after treatment with off-label dupilumab (a 600-mg subcutaneous loading dose followed by 300 mg every 14 days), his WI-NRS score was 0.
In a paper recently published in JAAD International, Dr. Kwatra, Ms. Manjunath, and coinvestigators reported on a series of 15 patients who developed chronic pruritus following an immune stimulus exposure, including immunotherapy and vaccination (2024 Apr 7:16:97-102. doi: 10.1016/j.jdin.2024.03.022). Most immunotherapy-treated patients experienced pruritus during treatment or after 21-60 days of receiving treatment, and the patients with vaccine-stimulated pruritus (after Tdap and messenger RNA COVID-19 vaccination) developed pruritus within a week of vaccination.
In addition to the elevated levels of IgE and eosinophils, plasma cytokine analysis showed elevated levels of IL-5, thymic stromal lymphopoietin, and other Th2-related cytokines and inflammatory markers in patients with immune-stimulated pruritus compared with healthy controls, Ms. Manjunath said at the meeting.
When a Malignancy Workup Becomes Important
The initial part of any diagnostic workup for CPUO should include CBC with differential, liver function tests, renal function tests, and thyroid function testing, said Kwatra, referring to a diagnostic algorithm he developed, which was published as part of a CME review in the Journal of the American Academy of Dermatology in 2022.
Then, as indicated by risk factors in the history and physical, one could order other tests such as HIV serology, hepatitis B/C serologies, bullous pemphigoid testing, chest x-rays, evaluation for gammopathies, stool examination for ova and parasites, or heavy metal testing. “Do you do everything at once? We like to keep it straightforward,” Dr. Kwatra said. “Depending on the patient’s risk factors, you could order more or less.”
A malignancy workup should be strongly considered in patients whose itch duration is less than 12 months — and especially if the duration is less than 3 months — with an emphasis on cancers more frequently associated with itch: Hematologic and hepatobiliary cancers. This is “when concern should be heightened ... when there should be a lower threshold for workup,” he said.
The 12-month recommendation stems from a Danish cohort study published in 2014 that demonstrated a twofold increased incidence of cancer among patients with pruritus in the first 3 months after the diagnosis of pruritus. The 1-year absolute cancer risk was 1.63%.
Other risk factors for underlying malignancy or malignancy development in patients with CPUO include age older than 60 years, male sex, liver disease, and current or prior smoking, according to another study, noted Dr. Kwatra.
Dr. Kwatra disclosed that he is an advisory board member/consultant for Pfizer, Regeneron, Sanofi, and other companies and an investigator for Galderma, Incyte, Pfizer, and Sanofi. Manjunath served as the codirector of the ElderDerm conference.
A version of this article first appeared on Medscape.com.