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A 31-year-old HIV-positive veterinary assistant presents with an erythematous smooth nodule on the shin with focal ulceration. There is regional lymphadenopathy. You forget to include the pertinent clinical history on the specimen requisition form and a diagnosis of “pyogenic granuloma” is rendered. Which of the following statements regarding this lesion is INCORRECT?

Part (A) reproduced, with permission, from Wolff K, Johnson RA, Saavedra AP. Fitzpatrick’s Color Atlas and Synopsis of Clinical Dermatology. 7th ed. New York, NY: McGraw-Hill Education; 2013.

A) The causative microorganisms are best highlighted with a Warthin-Starry stain, revealing granular clusters of bacilli within endothelial cells, macrophages, and within the dermis.

B) This condition is associated with exposure to cats and cat fleas.

C) Low-power microscopic examination will reveal a well-circumscribed pedunculated proliferation of small vessels with an overlying epidermal collarette.

D) These lesions typically respond to a course of antibiotics.

E) The endothelial cells will stain positive for HHV8 via immunohistochemistry.

The correct answer is E.

This patient has bacillary angiomatosis. This condition is a multiorgan infection caused by gram-negative Bartonella henselae bacilli. Cats and cat fleas classically transmit these organisms to immunocompromised patients. Clinically, the lesions may be solitary or multiple, depending on the immune status of the patient and the extent of the infection. Mucosal lesions may occur. Typically there is associated regional lymphadenopathy. These erythematous papules or nodules are smooth with frequent ulceration. Microscopically, there is a raised pedunculated proliferation of well-circumscribed small vessels surfaced by an epidermal collarette. The proliferation may be superficial, deep, or both, and is accompanied by a robust mixed inflammatory infiltrate composed of neutrophils, lymphocytes, plasma cells, macrophages, and leukocytoclastic debris. Vessels in the deep portions of the lesion may be collapsed without obvious lumina. On H&E, the bacilli appear as purple or amphophilic granular clusters within endothelial cells, macrophages, or within the dermis. Warthin-Starry or GMS stains should be ordered to better highlight the organisms.

Bacillary angiomatosis. Warthin-Starry stain reveals numerous black, clumped bacilli.

Immunohistochemical stains and PCR are also commercially available to confirm infection. B henselae is the causative organism of both bacillary angiomatosis and catscratch disease; however, unlike catscratch disease, these lesions do respond to antibiotic therapy. The differential diagnosis includes pyogenic granuloma, angiolymphoid hyperplasia with eosinophilia (epithelioid hemangioma), Kaposi sarcoma, and erythema elevatum diutinum. Pyogenic granuloma can appear very similar to bacillary angiomatosis. Lesions of pyogenic granuloma often have less of a neutrophilic infiltration and lack the clusters of bacilli. ...

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