A new association of cutaneous leishmaniasis with guselkumab in a patient with chronic psoriasis.

A 68-year-old White man presented with a 3-month history of two nontender, pruritic, erythematous plaques on his left arm. He had a medical history of chronic plaque psoriasis that has been stable on guselkumab treatment, an anti-interleukin-23 monoclonal antibody, for 5 years. The lesions persisted, despite topical treatments. His medical history also included previous cutaneous squamous cell carcinoma, recurrent penile Bowen disease and psoriasis that responded inadequately to -multiple biologics before the initiation of guselkumab. A biopsy of a persistent lesion was carried out, which confirmed the diagnosis of cutaneous leishmaniasis. Histopathology demonstrated extensive alignment of amastigotes along the peripheries of histocytes, a pathognomonic sign known as the 'marquee sign'. Physical examinations and serology were unremarkable. Polymerase chain reaction of the tissue biopsy identified possible involvement of Leishmania donovani and Leishmania mexicana. Unremarkable computed tomography of the thorax, abdomen and pelvis, and a negative rapid antigen K39 test eliminated the likelihood of visceral involvement. Discussion at a leishmaniasis multidisciplinary team meeting resulted in a final diagnosis of L. donovani cutaneous leishmaniasis. The patient recovered well after completing a 4-week course of oral miltefosine. Cases of leishmaniasis associated with the use of biologics associated have so far arisen mainly from tumour necrosis factor-α inhibitors. To our knowledge, this is the first documented case of cutaneous leishmaniasis in a patient treated with guselkumab. Our case emphasizes the importance of considering potential parasitic infections when faced with persistent lesions in patients who are immunosuppressed, especially those receiving biologic therapy.