A 17‐Year‐Old Girl With an Unusual Inflamed Papule on the Forearm

A 17-year-old female presented with a 2-week history of an inflamed papule on her right forearm. The lesion was occasionally pruritic. She has no relevant past medical history. The patient's father had a similar lesion on the hand that was previously treated. The patient did not present with fever or lymphadenopathy. On skin examination, a hyperkeratotic red papule with a verrucous appearance and ring of erythema was seen on the right forearm (Figure 1). The lesion measured ~1 cm in diameter. A shave biopsy specimen was obtained for histopathologic analysis (Figures 2 and 3). The biopsy revealed significant reticular degeneration of the epidermis with necrosis and spongiosis, without evidence of neoplasm. The dermis was markedly edematous and demonstrated a mixed inflammatory infiltrate that included eosinophils along with viral eosinophilic inclusions within the nucleus (Figures 2 and 3, H&E). The overall histologic appearance was compatible with orf. The patient's family raises sheep and the patient is frequently exposed to livestock. Orf is a zoonotic viral infection caused by the orf virus from the Parapoxvirus genus, and it can occur in humans handling sheep and goats. Humans who encounter infected animals, meat, and carcasses can contract orf via direct inoculation through abrasions or breaks in the skin. Loss of epithelial barrier integrity is the most common predisposing factor [1]. However, this patient did not have a prior diagnosis of atopic dermatitis. Orf can also be transmitted through knives, wool, buildings, and equipment previously in contact with infected animals [1]. In affected patients, clinical manifestations of orf usually occur on exposed areas such as the dorsal hands, fingers, forearms, and face. Orf can also occur on the axilla, scalp, buttocks, genitals, perianal skin, urethral skin, pericanthal eyelid skin, and conjunctiva. A small, red papule typically appears at the site of virus entry 3–7 days after inoculation and then develops into a hemorrhagic pustule or bulla, which will then produce a central crust and bleed. In later stages, the lesion may then weep (days 14–21) and then become dry with a thick crust. Most lesions naturally resolve between 3 and 8 weeks. Patients may also endorse fever, malaise, or lymphadenopathy [1, 2]. Cultural or religious practices involving animals increase the incidence of orf in addition to lack of public awareness [2]. The development of a nodule or papule with recent exposure to sheep or goats up to 1 week prior is highly suggestive of an Orf infection [3]. Orf in children is rare and presents similarly to adults with a self-limiting disease course. Lesions present in the typically exposed areas. Due to childhood behaviors, children are more likely to sustain animal bites or develop a lesion on the face, for example, due to nuzzling a lamb [4]. The histopathological features of orf vary according to clinical stage [1]. Intraepidermal vesiculation is present in early lesions. Later stages feature epidermal hyperplasia with a crust, epidermal vacuolation, viral eosinophilic inclusions in the nucleus or cytoplasm of keratinocytes, papillary dermal edema with diverse inflammatory infiltrate, and/or epidermal necrosis [2]. Culture is not used for diagnosis as it grows slowly and is not practical; therefore, PCR is the main modality used for diagnosis [3]. Other diagnoses to consider for eosinophils on biopsy from a papule include drug hypersensitivity syndromes [5]. The management of orf includes supportive treatment with wound care to decrease secondary bacterial infections. In immunocompetent individuals, orf is a self-limited disease that clears without scarring, and prognosis is excellent with no mortality reported [2]. Immunocompromised patients may experience persistent painful lesions measuring several centimeters in diameter. To treat immunocompromised patients, various methods have been reported, including intralesional interferon injections, electrocautery, topical imiquimod, topical cidofovir, and cryotherapy [3]. If the infection persists, wide local excision and skin grafting can be considered [1, 3]. However, long-term prognosis is still favorable in immunocompromised patients with early diagnosis and treatment. Reinfection is possible with exposure to the infected animal, though lesions are less severe and heal promptly in comparison to the initial infection [3]. Potential diagnoses to consider in the differential diagnosis include giant molluscum contagiosum, keratoacanthomas (KAs), and Mycobacterium marinum [1]. Giant molluscum contagiosum appears as flesh-colored umbilicated papules and has characteristic large intracytoplasmic eosinophil inclusion bodies known as Henderson-Paterson bodies on histopathology. Concerns for cosmesis and pruritus are common [6]. KAs often present with a central, yellow-brown, structureless keratin plug with elongated hairpin vessels [7]. Findings range from early exo-endophytic lobular proliferations of squamous cells with marked hyperkeratosis to keratin-filled craters with numerous squamous islands in the deep dermis in mature lesions and finally a flattening, atrophic epithelium [7]. KAs are rarely seen in children [8]. Mycobacterium marinum is a pathogenic mycobacterium causing skin and soft tissue infections associated with exposure to fish and water. Without this known exposure, diagnosis is usually delayed. In 60% of cases, M. marinum presents as a solitary papulonodular lesion on the finger or hand [9]. However, diagnosis relies on the isolation of M. marinum. Cultures are reported positive in 70%–80% of cases, but this number could be higher if kept at the optimal temperature for growth of 30°C [9]. The prevention of orf transmission to humans is possible through animal vaccination, wearing nonporous gloves when handling animal products, and practicing appropriate sanitation techniques. The ability to recognize orf papules is important, as an incorrect diagnosis can lead to unnecessary testing and treatments [3]. The authors declare no conflicts of interest.