An Uncommon Disease at an Unusual Site in a Female Child

A 7-year-old female child born of a non-consanguineous marriage presented with pruritic, hyperpigmented, papules involving the perineum for 6 months. Lesions initially appeared on the right side followed by involvement on the left, 3 months later. Family history was not contributory. Dermatological examination revealed grouped, hyperpigmented, hyperkeratotic, umbilicated papules involving the posterior aspect of genitocrural folds on both sides in the perineal region. Some of the papules coalesced to form plaques [Figure 1]. Systemic examination did not reveal any abnormality. Routine hematological and biochemical investigations were within normal limits. Serology for VDRL and retroviral status was negative.

Figure 1.

Hyperpigmented, keratotic, umbilicated papules involving genitocrural folds in the perineum

Histopathological examination revealed hyperkeratosis, acanthosis and cup-shaped depression filled with keratin, collagen and lymphocytes. The dermis showed thick eosinophilic altered collagen fibers with transepidermal elimination [Figure 2]. Masson's trichrome stain highlighted the presence of perforating strands containing collagen fibers [Figures 3 and 4].

Figure 2.

Cup-shaped depression filled with keratin, collagen and lymphocytes [H and E ×20]

Figure 3.

Dermal collagen stained blue showing transepidermal elimination [Masson's trichrome ×20]

Figure 4.

Perforating strands containing collagen fibers [Masson's trichrome ×20]

Question

What is your diagnosis?

Diagnosis

Reactive perforating collagenosis.

Discussion

Transepidermal elimination disorders (TEE) are characterized by elimination of altered dermal substances through perforating skin lesions. Reactive perforating collagenosis (RPC) is a rare type of TEE in which collagen is extruded through the epidermis. Mehregan et al., in 1967, described the first case of RPC in a 6-year-old girl.[1] Two forms exist: The inherited form with autosomal dominant or recessive trait seen in children and the acquired form seen in adults, associated with diabetes mellitus or chronic renal failure. The inherited form usually starts in infancy or early childhood indicating an inherited defect in the collagen and usually follows trivial trauma and tends to exhibit Koebner's phenomenon.[2]

RPC clinically presents as skin-colored, erythematous or hyperpigmented papules which become umbilicated, with a keratinous plug over few weeks, and it most commonly involves extensor aspect of hands, forearms, legs and face. However, less commonly affected sites include trunk, scalp and buttocks.[3] Involvement of perineum is an interesting clinical presentation in the present case, which has so far not been reported in the literature.

Bovenmeyer first experimentally induced lesions in a 4-year-old female child in extensor aspect of forearm, by scratching the skin with a 25-gauge needle.[4] Later, reproduction of RPC lesions by pinprick, scratching, superficial abrasion with 4-mm punch were reported.[5] RPC lesions are mostly evoked by superficial trauma and have been reported following insect bites, acne, cold exposure and at sites of corporal punishment.[5]

Superficial trauma in the form of scratching due to pruritus could have triggered the development of RPC in the present case. In addition, as Koebner's phenomenon, friction from edges of undergarments, the trauma encountered while sitting and contact with cold ground could be other contributory factors for the development of RPC in such unusual location.

It is hypothesized that in response to trauma, dermal connective tissue is injured, leading to alteration of papillary dermal collagen. Reactive epithelial hyperplasia occurs in the adjacent epidermis, whereas directly overlying epidermis becomes thin and show multiple foci of disruption, through which altered collagen and inflammatory cells are eliminated, similar to the histopathology in the present case.[5] In RPC, the extruded collagen is a histochemically altered but ultra-structurally intact type-IV collagen.[6] Trauma leads to the release of matrix metalloproteinases and serine proteases which transgress the epithelium and digest the extracellular matrix components and basement membrane structures contributing to the formation of perforating lesions.[7]

Differential diagnoses of RPC include molluscum contagiosum, papular urticaria, lichen planus, perforating folliculitis, perforating granuloma annulare and elastosis perforans serpiginosa. In the present case owing to the site of the lesion, initial erroneous diagnoses of molluscum contagiosum and genital wart were considered, suspecting sexual abuse because of increasing incidence of sexual offences against children in the present times. However, histopathology nailed the diagnosis of RPC, making it as one of the differential diagnoses to be considered, among the non-venereal genital dermatoses in the pediatric age group.

Treatment options include topical retinoic acid, steroids under occlusion, intralesional steroids, emollients, cryotherapy, oral isotretinoin, methotrexate, PUVA therapy and allopurinol.[2] The present case was treated with topical Tretinoin 0.025% cream and showed significant improvement after 3 months.

Learning Points

• RPC is a rare type of TEE, in which collagen is extruded through the epidermis

• Among the inherited and acquired forms, the former usually starts in infancy or early childhood indicating an inherited defect in the collagen and usually follows trivial trauma

• Histopathology is characterized by cup-shaped invagination of the epidermis, lined by an acanthotic epithelium along its sides, containing keratinocytes, inflammatory cells and degenerated collagen. Masson's trichrome stain confirms the presence of collagen fibers

• RPC most commonly involves extensor aspect of hands, forearms, legs and face

• Involvement of perineum is a rarity.