Clinical, Histopathologic, Immunohistochemical, and Electron Microscopic Findings in Patients With Cutaneous Monkeypox

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• In this retrospective histopathologic and immunohistochemical study, 20 patients with positive monkeypox virus DNA polymerase chain reaction were examined. Histopathology of all cutaneous lesions showed epidermal necrosis with surrounding balloon cell degeneration of epidermal and follicular outer root sheath keratinocytes. In early lesions, syncytial multinucleated cells with vesicular nuclei and prominent nucleoli were seen within areas of epidermal ballooning. Immunohistochemistry was positive for vaccinia antigen.
• Monkeypox lesions demonstrate epidermal necrosis and balloon cell degeneration of keratinocytes on histopathology. If needed, immunohistochemical staining for the vaccinia virus can help differentiate monkeypox from other conditions with similar histopathologic changes.

–  Katherine M. Stiff, MD

Abstract 

BACKGROUND

The worldwide outbreak of monkeypox has evidenced the usefulness of the dermatologic manifestations for its diagnosis.

OBJECTIVE

To describe the histopathologic and immunohistochemical findings of monkeypox cutaneous lesions.

METHODS

This is a retrospective histopathologic and immunohistochemical study of 20 patients with positive Monkeypox virus DNA polymerase chain reaction (PCR) and immunohistochemical positivity for Vaccinia virus in cutaneous lesions. Four cases were also examined by electron microscopy.

RESULTS

The most characteristic histopathologic findings consisted of full-thickness epidermal necrosis with hyperplasia and keratinocytic ballooning at the edges. In some cases, the outer root sheath of the hair follicle and the sebaceous gland epithelium were affected. Intraepithelial cytoplasmic inclusion bodies and scattered multinucleated keratinocytes were occasionally found. Immunohistochemically, strong positivity with anti-Vaccinia virus antibody was seen in the cytoplasm of ballooned keratinocytes. Electron microscopy study demonstrated numerous viral particles of monkeypox in affected keratinocytes.

LIMITATIONS

Small sample size. Electron microscopic study was only performed in four cases.

CONCLUSION

Epidermal necrosis and keratinocytic ballooning are the most constant histopathologic findings. Immunohistochemical positivity for Vaccinia virus was mostly detected in the cytoplasm of the ballooned keratinocytes. These findings support the usefulness of histopathologic and immunohistochemical studies of cutaneous lesions for diagnosis of monkeypox.

Journal of the American Academy of Dermatology

Clinical, histopathologic, immunohistochemical and electron microscopic findings in cutaneous monkeypox: A multicenter retrospective case series in Spain

J Am Acad Dermatol 2022 Dec 26;[EPub Ahead of Print], FJ Rodríguez-Cuadrado, L Nájera, D Suárez, G Silvestre, D García-Fresnadillo, G Roustan, L Sánchez-Vázquez, M Jo, C Santonja, MC Garrido-Ruiz, AM Vicente-Montaña, JL Rodríguez-Peralto, L Requena 

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Benjamin Hidalgo-Matlock
Skin Care Physicians of Costa Rica

Clinica Victoria en San Pedro: 4000-1054
Momentum Escazu: 2101-9574

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