Zanubrutinib-Induced Acneiform Rash in a Patient With Waldenstrom's Macroglobulinemia

Waldenström's macroglobulinemia is a rare lymphoproliferative disorder that can be treated with Bruton's Tyrosine Kinase inhibitors (BTKi), including zanubrutinib. Although zanubrutinib is associated with fewer off-target effects than first-generation BTKi, dermatologic toxicities may still occur. We report the case of an 81 year-old man with Waldenström's macroglobulinemia who developed a Grade I acneiform rash shortly after initiating zanubrutinib. The eruption, characterised by folliculocentric papules and pustules on the face and trunk, resolved with topical azelaic acid and salicylic acid, as well as oral azithromycin. Histology showed a perivascular and periadnexal CD3⁺ T-cell infiltrate without epidermotropism. A Naranjo score of 8 supported a probable drug reaction. This report highlights the need for awareness of cutaneous side effects associated with newer BTKi to ensure prompt diagnosis and optimal patient management.