Chapter 18: Chronic Pruritus of Unknown Origin

CHRONIC PRURITUS OF UNKNOWN ORIGIN

Therapeutic Approach

Chronic pruritus of unknown origin (CPUO) is a diagnosis of exclusion in patients presenting with chronic itch lasting greater than 6 weeks with no evidence of an underlying etiology. CPUO can be characterized by the presence or absence of Th2 polarization (also referred to as immunosenescence), which is suggested by increased blood eosinophils (eosinophil percentage ≥4% or absolute eosinophil count > 0.30 K/mm³) and/or elevated IgE (often ≥ 150 IU/mL).^1,2 The presence of either of these findings suggests inflammatory itch, and may predispose CPUO patients to success with immunomodulatory treatment such as methotrexate, whereas the absence of these findings suggests a greater role for neural sensitization and may indicate greater chance of therapeutic success with neuromodulatory treatments such as gabapentin.¹ There are few therapeutic trials for CPUO, with most evidence based on trials for other pruritic dermatoses. As a result, there are no FDA-approved therapies. Chosen therapy should be based on inflammatory phenotype, localization of itch, and clinical severity; periodic evaluation of CPUO patients should be conducted to identify pruritus as a presenting symptom of a systemic condition. See Table 18-1.