Cutaneous Infections

Cutaneous infections are one of the most common reasons for referral to and evaluation by pediatric dermatologists. Etiologic agents include viruses, bacteria, and less commonly, parasites. The majority of these infections are non-life-threatening and will resolve with treatment.

The following cutaneous infections are covered in this section:

• Molluscum Contagiosum

• Scabies

• Dermatophytosis

• Tinea Versicolor

• Warts

Molluscum Contagiosum

Molluscum contagiosum is a common skin infection that affects up to 11.5% of healthy children, with onset between ages 1 and 10 years. Molluscum are caused by a poxvirus and are transmitted through direct contact with infected individuals, autoinoculation, or contact with fomites. The exact incubation period is unknown but estimated to be between 2 weeks and 6 months.

Presentation: Clinically, molluscum present as 2- to 5-mm skin-colored papules with a central umbilication, most commonly on the trunk and extremities. In one study, 38% of patients with molluscum had an associated eczematous eruption (molluscum dermatitis), likely due to skin sensitization or scratching. When patients with atopic dermatitis develop molluscum contagiosum, they tend to have more lesions due to a compromised skin barrier.

The lesions, known as molluscum, are small, skin-colored or pink papules with a central umbilication. (Source: Molluscum Contagiosum. Centers for Disease Control 2015.)

Treatment: Molluscum is a benign skin condition with lesions that typically self-resolve over a period of a few months to several years in immunocompetent patients. However, treatment is frequently desired to alleviate symptoms (e.g., pruritus), decrease the chance of transmission, and normalize the appearance of the skin. A variety of treatments are often employed, although evidence of efficacy is limited.

• Cantharidin

  • Cantharidin is a topical vesicant that acts by producing small intradermal blisters.

  • Results of a placebo-controlled study support the safety and efficacy of topical cantharidin in pediatric patients.

  • The primary adverse effects are discomfort, an exuberant blistering reaction, dyspigmentation, and scarring.

  • Cantharidin is approved for use in Canada but is not currently approved by the FDA in the United States.

  • Two phase III trials of VP-102, a drug-device combination containing cantharidin 0.7%, showed superior efficacy in achieving complete clearance of molluscum contagiosum lesions, as compared to a vehicle without cantharidin.VP-102 is the first FDA-approved treatment for molluscum contagiosum.

• Cryotherapy

  • Cryotherapy is a destructive method that relies on very cold temperatures to induce separation between keratinocytes.

  • The primary adverse effect is discomfort, limiting its use in children.

• Physical destruction with curettage

  • Destruction with a curette targets removal of the poxvirus viral core.

  • The primary adverse effect is discomfort.

  • Curettage is a favorable option for patients with darker skin types, who may be prone to dyspigmentation with other destructive methods.

  • Curettage may be more effective than other modalities for larger molluscum with more-predictable resolution.

  • Numbing with topical or injection lidocaine prior to curettage can reduce the discomfort of the procedure.

• Topical retinoids

  • Topical retinoids act by creating irritation and inflammation.

  • Retinoids may be a good treatment for facial lesions, where other treatments cause too much irritation.

• Oral cimetidine

  • An oral histamine-2 receptor antagonist, cimetidine has shown efficacy in the treatment of warts and molluscum and is thought to enhance T-cell immunity.

  • This treatment may be a good option for patients who want to avoid procedural interventions and pain and for patients with multiple or refractory lesions.

  • Use for this indication is not FDA approved.

  • The primary adverse effect is gastrointestinal upset.

  • This treatment is more effective in younger children and patients with a history of atopic dermatitis; treatment may be dose-limiting in older children based on patient’s weight.

Reducing transmission and autoinoculation of molluscum

• avoid scratching

• handwashing

• occlusion of active lesions

• avoid contact sports unless lesions can be fully covered

• do not share baths or personal items (e.g., towels and clothing)

Exuberant or giant molluscum: Exuberant or giant molluscum can occur in immunosuppressed patients and may be more resistant to standard therapies.

Giant molluscum in a patient with a combined immunodeficiency syndrome due to an autosomal recessive DOCK8 mutation. (Source: Combined Immunodeficiency Associated with DOCK8 Mutations. N Engl J Med 2009.)

Facial molluscum in a patient with human immunodeficiency virus. (Source: Molluscum Contagiosum in a Patient with the Acquired Immunodeficiency Syndrome. N Engl J Med 1998.)

Scabies

Scabies is an infectious skin condition that is caused by the scabies mite Sarcoptes scabiei. Although scabies is a common infection worldwide and can occur in all settings, it disproportionately affects immunocompromised patients and people living in crowded environments.

The scabies mite is a parasite that completes its life cycle on humans. The female mites burrow in the skin and undergo a maturation process that lasts approximately 15 days. About 5 to 15 mites live on a human infected with classic scabies; the skin eruption is a consequence of the infestation and associated hypersensitivity reaction. Transmission generally occurs through direct close skin-to-skin contact for a period of at least 15 minutes. Occasionally transmission may occur through fomites.

Presentation: The clinical manifestation of scabies includes a rash and pruritus. In the classic adult presentation, lesions are most often found in the interdigital web spaces, flexor surfaces of the wrists, axilla, umbilicus, areola, and genitalia. In infants and young children, the distribution of lesions can also involve the scalp, face, palms, and soles. Scabies in young children may present in a vesicular, pustular, or nodular form and may mimic infantile eczema.

This mite was seen on direct examination of skin scrapings. The female mite dissolves the stratum corneum of the epidermis with proteolytic secretions and burrows downward. It is translucent, with brown legs; is 0.2 to 0.5 mm long; and is usually too small to see with the naked eye. (Source: Scabies. N Engl J Med 2006.)

An adult patient with excoriated papules on the back. Note the honey-colored crusting suggestive of secondary impetigo. (Source: Scabies. N Engl J Med 2016.)

Scabies in an infant localized to the feet. (Source: Scabies. N Engl J Med 2006.)

Interdigital lesions are a typical manifestation of classic scabies in adults (Panel A). A pattern of excoriated pustules in the axilla is characteristic of scabies with secondary bacterial infection (Panel B). (Source: Permethrin and Ivermectin for Scabies. N Engl J Med 2010.)

Diagnosis: The diagnosis of scabies is usually established clinically and confirmed by skin scraping with microscopic examination revealing mites, eggs, or scybala (feces).

Complications:

• Crusted scabies (formerly known as Norwegian scabies) is a form of hyperinfection caused by failure of the host’s immune system to control mite replication. It occurs in immunosuppressed patients (e.g., organ-transplant recipients or patients infected with human immunodeficiency virus). Patients with crusted scabies are infected with thousands to millions of mites. It is highly contagious through skin-to-skin contact or exposure to contaminated fomites.

Crusted scabies on the sole of the foot. (Source: Scabies. N Engl J Med 2006.)

• Bacterial superinfections (e.g., impetigo or ecthyma): Compromised skin barrier function can lead to superinfection with Staphylococcus aureus or Streptococcus pyogenes. Worldwide, secondary infection leads to a high burden of disease.

A patient with scabies superinfection presenting as impetigo. (Source: Scabies. N Engl J Med 2006.)

Treatment: No comparative studies have been conducted to evaluate the safety and efficacy of treatments for scabies in infants and children. Treatment options include:

• Permethrin cream (5%) is the recommended first-line treatment for scabies according to the CDC.

  • Treat the entire body (neck to feet) and include the head in infants.

  • Treatment should be repeated after 1-2 weeks.

• Ivermectin is an oral anthelminthic (two-dose series)

  • In a 2019 Cochrane review, permethrin cream had similar efficacy as ivermectin after week 2.

  • Ivermectin is not FDA approved for the treatment of scabies.

  • It should not be used for children weighing <15 kg.

• Sulfur ointment can be used in patients younger than 2 months and pregnant women.

• Benzyl benzoate lotion 10%-25%, although not available in North America, is considered an essential medicine by the World Health Organization.

• Topical glucocorticoids can be used for up to 4 weeks after treatment to treat symptoms of pruritus that persist called post-scabetic dermatitis.

People with prolonged exposure to an affected individual (including household members) should be treated at the same time as the affected person. Clothes and linens should be machine washed and dried with each treatment. Items that cannot be laundered can be treated with powdered or aerosolized insecticides or placed in a sealed plastic bag for 48-72 hours with each treatment.

The CDC provides information on prevention and control of scabies.

Dermatophytosis

Dermatophytosis (also referred to as ringworm due to its annular configuration) is a fungal infection of the skin. The different types of infection are named for the body location that is infected. The organisms that cause these infections are called dermatophytes and they belong to three common genera: Trichophyton, Microsporum, and Epidermophyton. Infection can be acquired from infected humans, animals, or the environment. For a broad overview of superficial fungal infections in children, see this review.

Presentation: Clinically, dermatophytosis presents as a pink or red annular eruption. The lesions can vary in size and classically have an active peripheral border and central clearing, helping to distinguish it from the primary differential diagnosis of nummular dermatitis. The presence of pustules, scale, or both is variable depending on the location of involvement. A superficial skin scraping with potassium hydroxide will reveal the presence of fungal elements and can aid in the diagnosis. A culture can also be obtained to confirm the diagnosis.

Note: A glass slide can be used to perform skin scraping in place of a scalpel to minimize the risk of injury in infants and young children.

• Tinea corporis is a dermatophyte infection of the skin on the trunk or extremities.

(Source: The image on the left is courtesy of Marcia Hogeling, MD. The image on the right is from Visual Dx.)

• Tinea capitis (ringworm of the scalp) is more common in children than adults. Transmission is more likely in crowded living quarters and occurs through direct contact with contaminated brushes and hair accessories. The classic presentation is a patch of alopecia with “black dots” that represent broken hair shafts. Less often, tinea capitis presents with widespread scaling of the scalp or as a pustular eruption. Associated occipital, posterior cervical, or postauricular lymphadenopathy can occur. Obtaining a fungal culture is helpful, and systemic antifungal therapy is required.

Tinea capitis presents with a scaly, pink plaque in the hair, often with associated lymphadenopathy. (Photograph courtesy of Carol Cheng, MD.)

• Tinea faciei is a dermatophyte infection of the face that is often a missed diagnosis and suspected after treatment failure of a presumed inflammatory dermatitis.

Tinea faciei presented as dry, scaly, erythematous, and annular lesions on the face in a young girl that requires treatment with oral antifungal. (Source: Tinea Faciei. N Engl J Med 2014.)

Treatment of dermatophytosis:

• Topical therapy with antifungal agents (e.g., azoles, allylamines, and ciclopirox) is generally considered first-line treatment.

• Treatment should be used twice daily for 2 to 4 weeks.

• Nystatin is not effective for dermatophytes.

• Oral therapy should be considered in cases of recurrence or treatment failure, widespread disease, for tinea capitis, and in the setting of immune system suppression.

• Consider obtaining a culture of skin scrapings to guide treatment selection.

Tinea Versicolor

Tinea versicolor is a superficial infection of the skin caused by fungi in the Malassezia genus.

Risk factors for tinea versicolor:

• warm temperature

• high humidity

• immunosuppression

• excessive sweating

• glucocorticoid use

Presentation: Tinea versicolor commonly presents as multiple monomorphic sharply demarcated oval macules and/or patches with fine scale. The color may be hypopigmented, hyperpigmented, or pink depending on the patient’s skin type. The lesions are characteristically located on the upper trunk, shoulders, or both.

(Source: The image on the left is from VisualDx. The image on the right is from Massachusetts Medical Society.)

Diagnosis: The diagnosis of tinea versicolor is established clinically. A superficial scraping of the skin, processed on a slide with potassium hydroxide, will reveal the presence of fungal hyphae and spores that resemble spaghetti and meatballs.

The differential diagnosis of tinea versicolor includes the following:

• pityriasis alba

• vitiligo

• pityriasis rosea

• postinflammatory hypo- or hyperpigmentation

• confluent and reticulated papillomatosis

• mycosis fungoides

Treatment: Tinea versicolor can be treated with a shampoo containing selenium sulfide or ketoconazole used as a body wash, ketoconazole cream, or in more extreme cases, oral fluconazole or itraconazole.

Warts

Human papillomavirus (HPV) is a double-stranded DNA virus that infects the skin and mucous membranes. More than 200 HPV serotypes have been identified; high-risk serotypes are associated with the development of carcinoma of the cervix, vagina, penis, anus, and oral mucosa. Most HPV infections are cleared by the host immune system.

Common warts (verruca vulgaris) are a common manifestation of HPV infection in children. Transmission occurs through direct skin-to-skin contact with an infected individual, through autoinoculation, or via fomites. An estimated 3% to 33% of pediatric patients are affected by warts, with a peak incidence in mid-childhood.

Presentation: On exam, common warts present as skin-colored hyperkeratotic papules. They classically interrupt dermatoglyphics (skin lines) and have central small black dots that represent thrombosed capillaries.

(Source: The image on the left is from VisualDx. The image on the right is from Massachusetts Medical Society.)

A hyperkeratotic, verrucous plaque and similar adjacent papules on the heel or weight-bearing areas of the foot. (Source: VisualDx 2016.)

Flat warts (verruca plana) are slightly elevated, smooth papules often located on the face and most commonly caused by HPV-3 and HPV-10.

Flat warts (verruca plana) are smooth, dome-shaped, and frequently smaller than common warts. (Photograph courtesy of Marcia Hogeling, MD.)

Treatment: The following are common treatment modalities for warts:

• active nonintervention

• topical salicylic acid (the only FDA-approved modality)

• destruction with cryotherapy

• topical imiquimod

• topical fluorouracil

• intralesional candida antigen

• contact sensitization with squaric acid dibutylester

• occlusion with duct tape

Condylomata Acuminata

HPV infection can cause condylomata acuminata (anogenital warts). These can be acquired sexually, via nonsexual heteroinoculation, or via vertical transmission. Lesions present as skin-colored pedunculated papules in the anogenital area. Genital warts in children can present a challenging situation given the concern for child abuse. Some experts argue that in children younger than 4 years, in the absence of other indicators of sexual abuse, the possibility of nonsexual transmission should be considered.

Treatment: Treatments include topical imiquimod, topical podophyllotoxin, and destruction with cryotherapy or surgery.

Prevention:

• HPV vaccine: In 2015, a 9-valent HPV vaccine (Gardasil 9) was FDA approved for ages 9 years and above.

  • This vaccine targets the HPV genotypes most commonly associated with HPV-related cancers. It does not target “low-risk” genotypes more commonly associated with nonanogenital warts.