Cowdry bodies

Cowdry bodies are intranuclear inclusion bodies formed during viral replication, representing accumulations of viral capsid proteins, DNA, and altered host chromatin. They are classified into two types:

- Type A Cowdry bodies: Large, eosinophilic inclusions surrounded by a clear halo, pushing host chromatin to the periphery of the nucleus ('owl's eye' appearance). Classically associated with Herpes Simplex Virus (HSV-1, HSV-2) and Varicella-Zoster Virus (VZV) infections, as well as Cytomegalovirus (CMV)-though CMV inclusions are sometimes described separately due to their very large, prominent halo. Seen in skin/mucosal lesions (e.g., herpetic vesicles), esophagitis, and encephalitis (HSV encephalitis - temporal lobe).

- Type B Cowdry bodies: Smaller, multiple inclusions without significant peripheral chromatin displacement; classically seen with poliovirus and adenovirus infections.

Clinically, identification of Cowdry type A bodies on Tzanck smear or biopsy supports diagnosis of herpetic infections (e.g., herpes labialis, genital herpes, varicella, zoster, or HSV encephalitis). The Tzanck smear, scraping the base of a vesicular lesion, shows multinucleated giant cells with these intranuclear inclusions in HSV/VZV infections but does not require Cowdry body identification alone-multinucleation is also key.

Histologically, these inclusions must be differentiated from other viral inclusions such as Negri bodies (cytoplasmic, rabies), Guarnieri bodies (cytoplasmic, poxviruses), and Bollinger bodies (cytoplasmic, poxvirus in birds).

High-yield exam associations: HSV encephalitis with hemorrhagic necrosis of temporal lobes showing Cowdry A bodies; varicella-zoster vesicular skin lesions; CMV infections (owl's eye inclusions, sometimes classified as distinct due to size).