Histopathologic examination of the biopsy specimen revealed an upper dermis that had several irregularly distributed capillaries with plump epithelioid endothelial cells. Punctate neutrophilic microabscesses were noted in an edematous stroma. There were clumps of amphophilic material in the interstitium that were were positive for bacilli on Warthin-Starry staining. The serologic titer for Bartonella henselae was positive at 1:256.
The plaques resolved, leaving postinflammatory hyperpigmentation, after a 4-week course of doxycycline (100 mg every 12 hours), and the therapy was continued for 2 more months.
Crusted Plaques in an Immunocompromised Host—Diagnosis. Arch Dermatol. 2005;141(2):263-268. doi:10.1001/archderm.141.2.264-b