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CASE REPORT
Year : 2022 | Volume
: 42
| Issue : 2 | Page : 145-147
Palmar wart with ‘Myrmecia’ inclusions on histopathology – recap of an unusual entity: a case report
Anshu Gupta Devra MBBS, MD (Pathology) , Salony Mittal, Awantika Tiwari
Professor Department of Pathology, School of Medical Science & Research, Sharda University, Greater Noida, Uttar Pradesh, India
Correspondence Address:
Anshu Gupta Devra
Flat No. 20104, ATS Advantage, Ahinsa Khand-1, Indirapuram, Ghaziabad, Uttar Pradesh 201014
India
Source of Support: None, Conflict of Interest: None
CheckDOI: 10.4103/ejdv.ejdv_26_21
Cutaneous warts are a common skin condition affecting children and young adults and signify infection with human papillomavirus. They are of various types and show association with specific viral genotypes. The aim of this case report is to highlight one such case of deep palmoplantar wart also known as ‘Myrmecia wart’ because of its very peculiar clinical and histopathologic findings. A young male in his mid-20s presented with a warty growth in the index finger of his right hand. Biopsy and subsequent histopathological examination confirmed its categorization as Myrmecia wart. A thorough account of its typical cytopathic effects observed in histopathology as well its differentiating features from other common warts like verruca vulgaris and molluscum contagiosum infection on microscopy is warranted. Further, not so frequent incidence merits detailed review of this entity.
Keywords: human papillomavirus, Myrmecia, palmoplantar wart
Cutaneous warts present clinically as skin-colored small, rough, and hard growths most of the time on hands and feet where they cause nothing more than cosmetic worries. They represent common viral infections of skin and mucosal epithelial cells caused by human papillomavirus (HPV).
Papillomavirus is a circular double-stranded nonenveloped DNA virus belonging to the Papillomaviridae family, it enters the mucosal and cutaneous epithelium through microcuts and abrasions where it inserts its viral genome in basal cells and uses the host’s machinery to replicate viral DNA and proteins. The dysregulation of host’s gene expression causes abnormal cell proliferation, in this case squamous cells [1]. Currently, 218 types of HPV have been isolated and identified as causing infections in humans. Of these, 45 infect the genital tract and the rest cause skin disease [2].
The cutaneous and mucosal manifestations of HPV infection include common wart verruca vulgaris, the genital wart condyloma acuminatum, and uncommon presentations like epidermodysplasia verruciformis. It is a known oncogenic virus with proven etiology in cervical and anogenital cancers [3].
Palmoplantar warts involve mostly palm and soles [3]. It consists of two distinct clinicopathological entities. First, the superficial mosaic type commonly presenting clinically as single or multiple sometimes confluent warty lesions in the dorsal aspect of fingers as painless, circumscribed, and firm elevated papules with papillomatous hyperkeratotic surface [3]. In contrast, deep palmoplantar warts are usually single, may rarely be multiple, but never coalesce. They have typical discoid structure, appearing as hyperkeratotic papules of the surface of which is granular keratotic sometimes dotted with blackish specks due to thrombosed capillaries [4] or sometimes covered with thick callus. Application of pressure causes sharp pain distinguishing it clinically from callous [4]. They affect children and adolescents more frequently [2].
Superficial mosaic warts have histological picture similar to verruca vulgaris and represent HPV 2 or 4 infection [3], whereas deep palmoplantar, also known as Myrmecia wart, is a deeper lesion like an iceberg, where only a small part is clinically visible, while most of the lesion is found in the deeper layers. They are associated with HPV-1 infection but can also be seen with HPV-60, 63, 65 [3].
Painful deep palmoplantar warts were known long back, first described by Celsus in 25 B.C. [4]. He called them ‘Myrmecia’ meaning ant’s nest. A detailed description of its clinical and histological features was given by Lyell, Bunting, and Pullar [4].
Case reportThe aim of this case study is to highlight one such case where a young 25-year-old male presented in skin OPD with a warty growth in the index finger of his right hand. The growth was excised and sent in 10% formalin for histopathology.
Grossly, the specimen consisted of a whitish irregular soft-tissue piece measuring 1×0.5 cm. The hematoxylin and eosin-stained sections revealed marked papillomatosis of epidermis with hyperkeratosis and focal parakeratosis ([Figure 1]). The keratinocytes in the middle showed intracytoplasmic eosinophilic inclusions of various sizes with nuclei at places showing nuclear enlargement, ground glass appearance, and focal viral inclusions ([Figure 2]), scant dermal tissue identified shows dilated blood vessels. The characteristic histologic findings and typical viral intranuclear inclusions clinched the diagnosis. Although myrmecia warts have peculiar histopathologic appearance, it has to be differentiated from superficial common mosaic-type palmar warts – Verruca vulgaris and molluscum contagiosum, both on clinical as well as histological grounds.
Figure 1 Palmar Myrmecia wart showing papillomatosis (star) and parakeratosis (arrow) – H&E ×200. H&E, hematoxylin and eosin.
Figure 2 Typical intracytoplasmic eosinophilic inclusions of varying sizes (star) and intranuclear viral-inclusion bodies (arrow), H&E ×400. H&E, hematoxylin and eosin. Discussion Deep palmoplantar Myrmecia warts are relatively rare as compared with their superficial mosaic-type counterpart that is verruca vulgaris. Myrmecia warts occur not only on palms and soles but also on the lateral aspects and tips of fingers and toes [5]. The diagnosis rests on identification of characteristic histological findings in a background of appropriate clinical setting.
Histologically, this lesion is characterized by predominantly endophytic growth with marked acanthosis and papillomatosis. The papillae are usually long and filiform. Hyperkeratosis is accompanied by parakeratosis and orthokeratosis, especially where there is interphase with normal epidermis. The distinct cytological features consist of multiple eosinophilic intracytoplasmic inclusions of varying size appearing first at the level of the second or third suprabasal cell layer progressively increasing in size, until they push the nucleus at the periphery [4]. The inclusion-laden keratinocytes are irregularly distributed among normal keratinocytes, thus disturbing the normal epidermal architecture and are more prominent in horny layer where they join with the parakeratotic layer. There is no stratum granulosum in-between [4]. Cytopathic effects of the virus are seen in nuclei of keratinocytes in the form of conspicuous basophilic nucleolus and round eosinophic inclusion of variable size surrounded by clear halo consisting of intranuclear viral particles [4].
This entity needs to be differentiated from common superficial palmar warts or mosaic warts and molluscum contagiosum. In contrast to Myrmecias, the superficial verrucous warts have exophytic growth with acanthosis, hyperkeratosis, and papillomatosis. There is no parakeratosis. The hyperplastic stratum granulosum has foci of clear vacuolated cells. Their cytoplasm may contain basophilic keratohyaline granules of even size, whereas in Myrmecia, intracytoplasmic inclusions are large, eosinophilic, and of variable sizes. The nuclei of mosaic warts can be large and vesicular but do not show distinct intranuclear viral inclusions.
Differentiating myrmecia from molluscum is easy on clinical grounds as it later presents as small, discrete waxy skin-colored umbilicated papules on trunk, axilla, and face. They rarely involve fingers and soles. Histologically they are characterized by cup-shaped indentation of the epidermis into dermis. The Henderson–Paterson bodies found in this are solitary large intracytoplasmic inclusion bodies that fill the entire cell compressing the nucleus into crescent form. Their color may vary from eosinophic to basophilic. Also, no intranuclear viral inclusions are observed in this in contrast to Myrmecia where they are readily apparent [6],[7].Although HPV-1, the causative agent of Myrmecia wart, is not known to cause latent infection, but Wititsuwannakul and Christine [5] in their study noted these viral inclusions as incidental histopathologic findings in four cases where the final diagnosis was different dermal pathology. Further, they noted them in specimens from unusual sites like eyebrows, scalp, forehead, and leg, suggesting that this cutaneotropic virus can have latent phase as well.
These warts are a visual delight for pathologist eyes because of their characteristic histology with typical viral cytopathic effects, which one remembers for lifetime.
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Conflicts of interest
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