Skin Disorders Guide

Diagnostic Hallmarks

1. Distribution: face and extremities (children); groin and genitalia (adults)
2. Tendency for clustered formation
3. Central umbilication

Clinical Presentation

Molluscum contagiosum occurs as skin-colored or white papules 2-10 mm in diameter. These papules are firm, smooth surfaced, and dome shaped. Occasionally, these lesions are translucent enough to erroneously suggest vesicle formation. A central umbilication is present in about 25% of lesions and, if visible, is a pathognomonic sign. Molluscum contagiosum may develop anywhere. In children the lesions are most often found on the face, arms, and trunk, whereas in adults they are usually present on the inner thighs, lower abdomen, or genitalia. When multiple lesions are present, they are frequently in a clustered pattern. Molluscum contagiosum is almost always asymptomatic. Clinical diagnosis can be confirmed by biopsy or by the extrusion of a characteristic white globule of viral protein through a central incision.

Course and Prognosis

As befits the name and viral origin, molluscum contagiosum is capable of spreading both to the patient through autoinoculation and to others through close personal contact. If it is left untreated, the number of molluscum lesions generally increases. In children and in persons who are immunosuppressed, this increase may be explosive, with 20-50 lesions occurring in a matter of several weeks. The growth phase is followed by a period of relative stability, and this in turn is succeeded by a final phase, 12-24 months later, of spontaneous resolution. Subsequent reinfection does not commonly occur. Traumatic extrusion of viral protein into the surrounding dermis sometimes develops in one or more lesions. This leads to an inflammatory response that is occasionally brisk enough to simulate furunculosis.

Causes and Symptoms

The lesions of molluscum contagiosum are caused by two closely related DNA viruses (MCV-l and MCV-2) of the poxvirus group. Viral particles are inoculated into the epidermis as a result of cutaneous trauma during close personal contact. After an incubation period that averages about 1-2 months, viral replication begins within the cytoplasm of the midepidermal keratinocytes. This leads to epithelial cell proliferation and subsequent development of a visible papule.

The parasitized epidermal cells are recognized as a central white globule of viral protein that can sometimes be extruded through the characteristic umbilication. Presumably, spontaneous release of these cells accounts for spread of virus to other areas of skin or to other people.

The molluscum contagiosum virus cannot be cultured, and thus Koch’s postulates have not been fulfilled. Antibody response to molluscum contagiosum virus infection does occur, but resolution of the lesions probably depends on the triggering of a cell-mediated immune response.

Therapy

Molluscum contagiosum, though harmless, are usually treated because of the potential for spread. In very young children the application of cantharidin (Cantharone) results in the formation of a subepidermal blister containing the wart in its roof. Spontaneous sloughing of the roof and contained wart occurs 7-10 days later. The whole process is essentially painless. In older children and adults, cryotherapy with liquid nitrogen, application of trichloroacetic acid, incision followed by curettage, and, possibly, repeated applications of podophyllotoxin, work reasonably well. Electrosurgery, laser ablation, and excision should be avoided, as they may result in scarring.