The Mysterious Nodule on the Thigh.

Case Report

A 24-year-old unmarried healthy female presented with a single painful nodule on the medial aspect of left thigh since 2 months. She reported previous history of boil at the same site 1 year ago which subsided on treatment. Patient was not a known diabetic and denied any previous history of trauma or bleeding from the site. She also denied using any topical medicaments at the site. On dermatological examination, an erythematous sessile nodule of size 1.5 cm × 1 cm was seen 5 cm away from the groin fold [Figure 1]. On palpation, the nodule was tender and firm in consistency. Systemic examination was within normal limits. Her laboratory evaluation and screening for biopsy were within normal limits. Excisional biopsy of the complete lesion was done and subjected to histopathological examination. Histopathology showed hyperplasia of contiguous follicular infundibula with numerous eosinophilic bodies within the spinous cells [Figures 2 and 3].

Figure 1

Erythematous sessile nodule

Figure 2

Hyperplasia of contiguous follicular infundibula (H and E, ×4)

Figure 3

Numerous eosinophilic bodies within the spinous cells (H and E, ×40)

Answer

Molluscum contagiosum.

Discussion

Molluscum contagiosum is a common cutaneous infection caused by virus belonging to poxvirus family. In children, it occurs due to direct skin-to-skin contact and via fomites, whereas in adults, it is often a sexually transmitted disease or occurs in association with immunosuppression. The characteristic lesion of molluscum contagiosum is a pearly white, pink to translucent papule with central umbilication. It can be solitary or multiple with the common sites of involvement being areas of skin friction or moist regions like axillae, groin, popliteal fossa, genital, or perianal areas. Our patient presented with an exophytic lesion at the site of a previous painful lesion, which was possibly a furuncle. Since the lesion was not on the genitalia and she was not immunosuppressed, a diagnosis of molluscum was not considered clinically. Instead it appeared like an infected and macerated achrocordon. However, histopathological examination showed hyperplasia of contiguous follicular infundibula, each of which showed lobulated hyperplasia and the periphery showed keratinocytes with prominent nuclei. The center had numerous eosinophilic intracytoplasmic bodies within the spinous cells, known as molluscum bodies or Henderson Paterson bodies. The surrounding dermis showed diffuse dense mixed infiltrate of lymphocytes and neutrophils, some of which were spilling into the involved follicular infundibula with the overlying epidermis showing moderate spongiotic psoriasiform change suggestive of an inflamed lesion of molluscum contagiosum. Thus, an unusual presentation of giant molluscum contagiosum mimicking an infected achrocordon was confirmed. This response in which an unrelated or different disease occurs in an already healed lesion is known as Wolf's isotopic response.[1] In our case, a solitary lesion of molluscum contagiosum occurred in a previously healed lesion of furuncle. Atypical lesions of molluscum contagiosum measuring >1 cm2 are known as giant molluscum contagiosum.[2] A review of literature showed that isolated giant molluscum contagiosums mimicking epidermoid cyst, pyogenic granuloma, and keratoacanthoma have been described on the upper eyelid, cheek, and the angle of the mouth in immunocompetent individuals.[23456] Majority of these lesions were found in children.[245] Some of these lesions showed brain like sulci and gyri on gross examination after excision and some of them extruded paste like material on palpation.[245] However, the lesion in our case neither extruded paste like material on palpation nor showed sulci and gyri on gross examination after excision, thereby increasing the diagnostic dilemma. Therefore, molluscum contagiosum should also be included in the list of differential diagnoses of a solitary nonhealing exophytic nodule at the site of previous dermatoses or trauma. Treatment of molluscum contagiosum is desirable, if the rate of spontaneous resolution is slow or lesion is symptomatic and the choice of treatment depends on the age of the patient and number of lesions. It includes agents that either stimulate an immune response against the viral antigen or directly damage the virus or infected cells. Among the various topical agents, commonly used are cantharidin, trichloroacetic acid, retinoids, salicylic acid, 5%–10% KOH, tea tree oil, benzyl peroxide cream, and imiquimod. Other treatment options that can be tried are cryotherapy, intralesional immunotherapy, oral cidofovir, and surgical removal of the lesion.

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Nil.

Conflicts of interest

There are no conflicts of interest.