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Researchers propose use of ‘chronic pruritus of unknown origin’ designation

Researchers recommend new nomenclature of “chronic pruritus of unknown origin,” or CPUO, a diagnostic workup and classification to help increase the understanding of chronic pruritus.

“We propose the terminology CPUO to acknowledge our limited understanding of the condition and likelihood that a number of etiologies are likely to be unmasked in the near future,” Brian Kim, MD, associate professor of dermatology at the Washington University School of Medicine, and colleagues wrote.

The term “generalized” should not be used due to the extent to which the condition can vary.

“In our opinion, if there is well-understood etiology underlying a specific condition, then CPUO is excluded as a diagnosis. If it is suspected that an etiologic agent is causing pruritus, then if patients improve upon cessation and/or relapse upon repeat exposure, they would also not have CPUO,” the researchers wrote.

They added that CPUO encompasses conditions previously known as Willan’s itch or pruritus of the elderly. In many cases, pruritus of the elderly is the same condition as CPUO, as the etiology remains unknown.

“This is a proposed modification from the British Academy of Dermatology guidelines. It is important to note, and we acknowledge, that the definition of CPUO is likely to become more restricted as etiologies are identified for subsets of conditions currently within this category,” the researchers wrote.

Next, the diagnosis of CPUO excludes primary dermatologic or other underlying medical disorders.

For patients with CPUO, extensive diagnostics are common, they wrote. Ancillary testing should be confined to the dermatology clinic, along with a thorough history, exam and referral.

The proposed recommended diagnostic workup for CPUO should occur around a time frame of 6 weeks or longer with no primary rash. Medical history should include timing, location and duration of pruritus, medication and comorbidities and environment.

The physical examination should include the complete body, including the genitals, to rule out scabies, and look for primary lesions.

In all patients, clinicians should order a CBC laboratory test with differential, liver function tests, renal function tests and thyroid function tests.

A skin biopsy is recommended, but not required for anyone who has a history of a skin lesion in a pruritic site or if suspicion for latent pruritic dermatoses is high based on history or risk factors like dermatitis herpetiformis or bullous pemphigoid in those aged at least 65 years.

If a malignancy is suspected, refer the patient for malignancy screening, according to researchers. Similarly, refer the patient in the case of a suspected neurologic cause.

If there is no primary cause identified, diagnose as CPUO and continue empiric antipruritic treatments, they wrote. – by Abigail Sutton

Disclosures: Kim reports he was supported by grants from the American Skin Association, the Doris Duke Charitable Foundation, LEO Pharma and the NIH NIAMS. He has served as a consultant for AbbVie, Concert Pharmaceuticals, Incyte Corp., Menlo Therapeutics and Pfizer. He is a stockholder, founder and chief scientific officer of Nuogen Pharma. Kim has participated on advisory boards for Cara Therapeutics, Celgene Corp., Kiniksa Pharmaceuticals, Menlo Therapeutics, Regeneron Pharmaceuticals, Sanofi and Theravance Biopharma. Please see the study for all other authors’ relevant financial disclosures.