Which diagnosis is indicated by multinucleated giant cells found in a Tzanck preparation of labial lesions?

The presence of multinucleated giant cells in a Tzanck preparation is highly indicative of Herpes Simplex Virus (HSV) infection. Tzanck smears allow for rapid microscopic examination of skin lesions and are particularly useful for diagnosing herpesvirus infections. In cases of HSV, the virus causes the infected epithelial cells to fuse, leading to the formation of these giant cells, which possess multiple nuclei.

This finding supports the diagnosis of herpes simplex virus more than any of the other listed options. Molluscum contagiosum, while it is a viral infection that can cause skin lesions, typically presents with a different histological appearance that includes molluscum bodies rather than multinucleated giant cells. Human papilloma virus (HPV) is associated with warts and lesions that exhibit koilocytic changes on cytology rather than giant cells. Syphilis, caused by Treponema pallidum, does not show multinucleated giant cells on Tzanck preparations; instead, it has distinct histopathological features.

Thus, the presence of multinucleated giant cells in this context is a classic sign consistent with HSV infection.