A 45-year-old woman with HIV comes to the office due to the appearance of multiple tender nodules on her lower extremities over the past several weeks. The patient tried to squeeze open the lesions, but this led to profuse bleeding with no expression of pus. She works at a pet store in Mississippi and has regular contact with a variety of animals. Skin examination findings are shown below.
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Biopsy of the lesions reveals large endothelial cells forming vascular channels with a mixed neutrophilic and lymphocytic infiltrate. Immunohistochemical staining for human herpesvirus 8 is negative. Infection with which of the following pathogens is most likely responsible for this patient's skin condition?
Bacillary angiomatosis (BA) is characterized by the formation of highly vascular lesions in the skin and other organs due to infection with the small, gram-negative bacterium Bartonella henselae. The major reservoir for this organism is domesticated cats, and transmission to humans primarily occurs after a cat scratch or bite. Patients with intact immunity who are exposed to B henselae often develop cat-scratch disease (regional lymphadenopathy), but those with advanced AIDS are at risk for the more severe clinical syndrome of BA.
Patients with BA develop violaceous, cutaneous lesions that are highly vascular. Lesions form over weeks or months and are typically associated with fever, weight loss, and other constitutional symptoms. As these lesions are similar to those seen in Kaposi sarcoma, tissue testing for human herpesvirus 8 (HHV-8) is typically performed (HHV-8 testing will be positive in Kaposi sarcoma and negative in BA). Biopsy with histopathology confirms the diagnosis and usually reveals large endothelial cells forming small vascular channels surrounded by a mixed inflammatory infiltrate. Modified silver stain can also identify the organism.
(Choice A) Actinomyces israelii is a branching, gram-positive bacterium that grows in filaments. It primarily causes a cervicofacial infection that begins as a slowly growing mass which evolves into multiple abscesses and draining sinus tracts with yellow ("sulfur") granules. Histopathology typically shows chronic inflammatory granulation tissue surrounding dense fibrosis.
(Choice C) Blastomyces dermatitidis is a dimorphic fungus that primarily causes acute or chronic pneumonia but can also spread to the skin, leading to verrucous lesions with irregular borders. Culture is usually required for diagnosis and histology will show granulomas.
(Choice D) Mycobacterium marinum is a nontuberculous mycobacterium that is found in fresh and salt water. It can inoculate areas of broken skin (eg, abrasions) and result in an infection marked by cutaneous papules, ulcers, and scarring. Histology reveals granulomatous inflammation.
(Choice E) Staphylococcus aureus skin infections (eg, folliculitis) are more common in patients with HIV. However, these infections typically develop over a few days and are associated with purulent fluid.
Educational objective:
Bacillary angiomatosis is primarily seen in patients with advanced AIDS. It is caused by the gram-negative bacterium Bartonella henselae, which is typically transmitted by a cat scratch. Patients usually develop highly vascular, violaceous, cutaneous lesions over weeks or months. Histology of the lesions reveals large endothelial cells forming small vascular channels with a surrounding inflammatory infiltrate.