J Cutan Pathol 2010: 37: 282–286
doi: 10.1111/j.1600-0560.2009.01298.x

Background: Molluscum contagiosum (MC) causes characteristic cutaneous lesions that occur mainly in children, sexually active adults, and immunocompromised individuals, especially those with human immunodeficiency virus (HIV) infection. Patients infected with HIV, particularly those with advanced disease, have an increased incidence, up to 33.3%, of MC in non-anogenital areas. MC has been rarely found to be associated with epidermoid cysts.
Case report: A 44-year-old male with HIV infection presented with the complaint of a-3-month history of a tender nodule on the left neck. H&E stained sections showed a ruptured cyst, lined with squamous epithelium showing cytopathic changes of MC, and a xanthogranuloma-like inflammatory reaction with characteristic Touton-type giant cells.
Conclusion: MC infections are common, however MC associated with epidermoid cysts is infrequent. A few cases of MC occurring in epidermoid cysts have previously been reported. We are presenting a case of MC involving an epidermoid cyst in an AIDS patient, with a unique xanthogranuloma-like reaction. Xanthogranulomatous (XG) reactions have been infrequently reported in association with other viral infections, however, poxvirus-associated XG reaction has only been observed in animals. This is the first reported case of MC-associated XG reaction in humans.

Aldabagh B, Ly MN, Hessel AB, Usmani AS. Molluscum contagiosum involving an epidermoid cyst with xanthogranuloma-like reaction in an HIV-infected patient.
J Cutan Pathol 2010; 37: 282–286.

Introduction

Molluscum contagiosum (MC) is a cutaneous papular infectious disease caused by four closely related types of DNA poxviruses, MCV 1–4, and their variants.1 MC, originally described by Bateman,2 causes papular cutaneous lesions that mainly affect children, sexually active adults and immunocompromised individuals, especially those with HIV (human immunodeficiency virus) infection. Histologic features compatible with MC have been rarely reported in some epidermoid cysts.3–8 Patients infected with HIV-1 have an increased incidence of MC, and most have advanced disease with CD4 counts below 100 × 106/ L.9–12 There are rare reported cases of MC associated with folliculitis and epidermoid cyst in HIV patients.13,14 We are presenting, to our knowledge, the first case of MC in an epidermoid cyst with a peculiar xanthogranulomalike reaction in a patient with AIDS, which has not yet been reported in humans.

Case report: A 44-year-old male with HIV infection and CD4 count of 16 × 106/ L presented with a 3-month history of a tender nodule on the left neck. The lesion was an elevated firm inflamed subcutaneous nodule measuring 1.5 × 0.7 cm. The surface was erythematous, warm, and tender to palpation. However, there was no surface scale, punctum, or erosion. The clinical impression was an inflamed and ruptured epidermoid cyst, which was subsequently excised. The patient also had multiple white-topped umbilicated papules with size ranging from 3 to 1.8 cm on the neck, beard area, and left axilla. The patient had a history of squamous cell carcinoma and disseminated Mycobacterium avium infection, as well.

Histopathologic examination:
The excised specimen consisted of an elipse of skin and fragments of subcutaneous tissue. Hematoxylin & eosin (H&E) stained sections showed a cystic space in the deep dermis, the lining of which was mostly detached (Fig. 1). The intact portion of the cyst was lined by hyperplastic squamous epithelium which showed cytopathic changes, characteristic of MC (Fig. 2). The cells contained large red to blue cytoplasmic inclusions pushing the hyperchromatic and shrunken nuclei against the cell membrane (Fig. 3). There was associated dense granulomatous, suppurative, and chronic inflammation consistent with cyst rupture. Interestingly, there were collections of pale and foamy histiocytes with interspersed lymphocytes (Fig. 4) and occasional Touton-type giant cells giving the infiltrate a xanthogranulomalike appearance (Fig. 5). Occasional macrophages, containing amorphous material, were also noted which may represent engulfed viral particles (Fig. 6).

Discussion

Eleven cases of MC occurring in epidermoid cysts have been reported and are summarized in Table 1. In most of the cases, the HIV status of the patients was unknown. Smith et al.14 described one case of MC in an epidermoid cyst in an HIV patient. We are presenting another case of MC involving an epidermoid cyst in an AIDS patient, with a unique xanthogranuloma-like reaction. Poxvirus-associated xanthogranulomatous (XG) reactions have been observed in animals,15 however it has not yet been observed in humans.

MC often occurs in young children, sexually active adults and immunosuppressed persons, especially those with HIV infection. MC is caused by four closely related double stranded DNA-type of poxviruses, MCV 1–4 (MC virus), and their variants. MCV-1 infections are most common, and virtually all pediatric infections are caused by MCV-1.15,16 In patients infected with HIV,MCV-2 cause 60% of the infections,15,16 suggesting that HIV infection associated with molluscum does not represent recurrence of childhood molluscum.1 Almost 90% of adults have been shown to have antibodies to MC.17 However, clinical lesions are rarely observed in adults in nonanogenital areas when cellular immunity is intact. Molluscum is easily transmitted by direct skin-to-skin contact, especially if the skin is wet. Lesions are characteristically 3–5 mm smooth, firm, dome-shaped papules with a central umbilication. In children, lesions tend to be on the face, trunk, and extremities. In adults, molluscum is often sexually transmitted; and the distribution favors the lower abdomen, upper thigh, anus and in men, the penile shaft.1

Patients infected with HIV have an increased incidence of MC, especially with advanced disease.9,10,18 Among persons infected with HIV, the prevalence of Fig. 5. Touton-type giant cells, typically seen in xanthogranuloma, are also noted. Fig. 6. A focus of granulomatous infiltrate with inclusion-like material in a macrophage. MC has been reported to range from 5 to 30%.1 A study by Koopman et al.19 on 72 patients with HIV reports the prevalence of MC lesions in patients with low CD4 counts (below 100 × 106/ L) to be as high as 33.3%. In another study of 27 patients with HIV infection, the mean CD4 count was 86 × 106/ L.12 There was also a statistically significant correlation between the CD4 count and extent of MC infection.12 In addition to a reduction in CD4 lymphocytes, a decrease in Langerhans cells in AIDS may also be a factor in the pathogenesis of MC.19 A lack of Langerhans cells is the characteristic of lesional skin of MC in non-HIV-infected persons.20,21

Table 1. Previous reports of MCV located in cysts

Table 2. Virus-associated granulomatous/xanthogranulomatous reactions (XG)

An interesting observation in our case was a tissue reaction similar to xanthogranuloma on microscopic examination in areas of epithelial denudation. This type of tissue reaction has not been described in association with epidermoid cyst rupture. A literature search revealed a few reports of virus-associated XG reactions. (Table 2).22– 24 Pinkus et al., in 1949, while studying inflammatory reaction to inoculated MC in humans noted a lymphohistiocytic reaction.25 Mehregan also described a granulomatous reaction in association with MC lesions in some of their 42 cases of MC.26 And finally, Niven et al. noted a granulomatous reaction in lesions of monkeys that were experimentally produced by poxvirus inoculation.15

XG reaction is not an uncommon inflammatory response and occurs in many organs and tissues. Cyst-associated XG reaction in extracutaneous sites have also been reported in the literature including several cases of colloid cysts of the third ventricle and cerebellar vermis,27– 30 urachus 31,32 and the subglottis.33 However none of these cases appear to be associated with the viral infection.

In the skin, it has been suggested that the preferred site of inoculation of MC virus is infundibular epithelium,34 which would explain cyst formation occasionally associated with MC lesions. Perhaps, the resulting infundibular epithelial hyperplasia following viral inoculation, in some case, occludes the infundibulum resulting in cystic dilation of the proximal portion of the hair follicle.

Herein, we describe a case of virus-associated XG reaction in a setting of MC-infected epidermoid cyst. In conventional MC infection, an inflammatory response is not induced because of localization of the virus to the epidermis. In our case, the dermal tissue was exposed to the viral particles because of the association with an epidermoid cyst and its subsequent rupture. The immunecompromised state of our patient may also have contributed to this peculiar inflammatory response.

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