- Hyperplastic acanthotic epidermis show invagination of epidermal cells in dermis.
- The keratinocytes show large round to ovoid, dense eosinophilic intracytoplasmic inclusions (Molluscum bodies/ Henderson-Paterson bodies, marked with blue arrow) with peripheral displacement of dark blue nuclei (marked with green arrow). Marked areas with red arrow highlight the numerous small pink granules, which fuse and form characteristic Molluscum bodies.
- Disintegration of stratum corneum with cup shaped crater is seen with extrusion of molluscum bodies
- Inflammatory reaction is not seen
Practical Points of Pathoclinics:
- Molluscum contagiosum is a self-limited infectious skin disease. It is caused by molluscum contagiosum virus (MCV) (Double stranded DNA poxvirus). Molluscum contagiosum is common in children (MCV1 type) and immunocompromised /HIV positive adults (MCV2 type). Route of transmission are sexual contact, close contact, fomites or infected swimming pool water . Skin lesions develop after around 2 to 7 weeks after inoculation of virus. Auto-inoculation can be seen in molluscum contagiosum.
- Clinically, varying numbers of lesions (single or multiple), characterized by pale pink/flesh coloured, small, discrete, waxy, firm, dome shaped umbilicated papules (2-5 mm) (central depression). Umbilicated lesion may get ruptured, and cheesy material (actually molluscum bodies) may come out. Sometimes giant lesion (giant molluscum) may be seen. Lesions of molluscum are usually asymptomatic. Common sites are face, neck, hands, and genital region. In immunocompetent, the lesions regress spontaneously. In immunosuppressed or HIV positive, widely disseminated lesions can reach up to considerable size. Lesions last for several months, but the disease may persist for several years.
- The characteristic histologic feature is Henderson-Patterson inclusion bodies/Molluscum Bodies, which can be seen on squash preparation of lesion, which gives a rapid microscopic diagnosis. Initial changes of molluscum contagiosum are epidermal oedema in the basal layer and fusion of small granules resulting in oval eosinophilic bodies in the stratum malpighi.
- Histopathologically, acanthotic epidermis with proliferation and invaginations of epidermal cells with large round to ovoid intracytoplasmic inclusion bodies (molluscum bodies, also known as Henderson–Patterson bodies). Molluscum bodies are smaller and eosinophilic in colour in deep portions of epidermis (just above the basal cell layer) while relatively larger and more basophilic in appearance in the upper epidermis (granular layer). The nucleus is compressed and displaced by these bodies. Molluscum bodies release due to disintegration of stratum corneum, form the central crater (cup shape lesion) and surrounded by eosinophilic horny fibers. Reactionary inflammatory reaction comprising of lymphocytes (CD8 cytotoxic T cells), neutrophils and granulomas can be seen in dermis, which may partially obscure the molluscum bodies but not impinge on diagnosis.
- Molluscum bodies contain the poxvirus particles, readily identified on electron microscopy.
- The histopathology of molluscum contagiosum is very characteristic and rarely produce diagnostic difficulties. However, deep plantar wart (myrmecia) may mimic the molluscum contagiosum, especially to newer pathologist. In wart, presence of marked acanthosis and large, irregular, homogeneous eosinophilic intracytoplasmic inclusion bodies in the cytoplasm of HPV infected keratinocytes in the stratum spinosum, may mimic the molluscum bodies. Here feature like striking hyperkeratosis, papillomatosis and hypergranulosis along with koilocytotic changes should be searched for a diagnosis of planter wart.
- Molluscum contagiosum is a self-limited disease. Destruction of the lesions by cryotherapy, curettage, or other chemical methods can be done for cosmetic reasons or concerns of transmission and autoinoculation.
- Leung AKC, Barankin B, Hon KLE. Molluscum Contagiosum: An Update. Recent Pat Inflamm Allergy Drug Discov. 2017;11(1):22-31. doi: 10.2174/1872213X11666170518114456. PMID: 28521677.