Molluscum contagiosum (MC) is an infectious skin disease known to be caused by a poxvirus. It generally appears as multiple flesh-colored papules with central umbilical depression in children. Adult cases are relatively rare, and atypical clinical features in these cases can mimic various diseases, which sometimes makes diagnosis difficult. Herein, we report a case of MC with an atypical clinical and dermoscopic presentation in an adult patient.

A 64-year-old male patient presented with enlarged inguinal lymph nodes. The lymph nodes' pathologic findings showed atypical monoclonal CD4+ T cell infiltration, and radiologic studies disclosed multiple involved ilioinguinal lymph nodes. As a result, the patient was diagnosed with malignant lymphoma with peripheral T cell lineage. A skin lesion developed on the right leg and was observed over serial visits to the hemato-oncology department. A consult to the dermatologic department was recommended for further evaluation. A 6-mm pruritic, erythematous nodule with scales and ulcer in the center was observed (Fig. 1A). The initial clinical impression was prurigo nodularis. Dermoscopy showed a reddish to whitish structure with surface scaling, central ulceration, and dotted vessels (Fig. 1B). A punch biopsy was performed for differential diagnosis. Histopathologic findings showed inverted lobules of the acanthotic epidermis with central crater. In the crater, a characteristic intracytoplasmic eosinophilic inclusion body (molluscum body) was found (Fig. 1C). The final diagnosis was MC.

MC generally appears as multiple papules with sizes ranging from 3 to 5 mm. However, in adults, MC may manifest with atypical patterns unlike in children, resulting in a challenging diagnosis. In 28 cases of MC in Korean adults, atypical clinical findings were found in most patients (18 cases, 64.3%). They were initially mistaken for warts, folliculitis, and chickenpox. Also, when MC presents as nodules or tumors, they can be mistaken for epidermal cysts, pyogenic granulomas, warts, soft fibromas, basal cell carcinomas, keratoacanthomas, and prurigo nodularis. Making an accurate diagnosis is crucial considering the different treatment modalities.

Although the histopathology revealed an evident molluscum body, dermoscopic findings did not demonstrate central whitish structures. This made the diagnosis difficult in this case. It is possible that the central whitish structures were disguised due to the ulcerative changes in the stratum corneum layer. As MC in adults can manifest with various clinical presentations, a differential diagnosis of MC cannot be excluded even in the absence of the aforementioned features. Further studies regarding diverse clinical and dermoscopic features of MC are warranted.

In conclusion, we report a case of MC with atypical clinical and dermoscopic features in an adult patient. A more prudent examination is necessary for cases involving adult patients.

Figure 1. (A) An erythematous round nodule with central crust and scale on the leg, (B) Dermoscopy shows a reddish to whitish structure with scale, central ulceration, and dotted vessels. (C) Pathology of the nodule demonstrates lobulated hypertrophied epidermis forming a central crater which is filled with molluscum bodies (H&E, ×40).

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