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Case Note

Case Note: Pruritic Eruption on the Scalp and Neck

History

A 15-year-old healthy female high-school student, with no significant past medical history, presents for management of pruritic eruption on the scalp and neck.

Initial evaluation

  • Healthy-appearing female
  • No significant past medical history
  • Presents for management of 6 weeks' history of intensely pruritic eruption on the scalp and neck
    • Scattered erythematous macules and excoriated papules on the neck
    • No evidence of superinfection
  • Denies recent travel or new cosmetics for hair or skin
  • Image 1
    Image 1

Enter your diagnosis

Diagnosis

  • In addition to the patient symptom presentation, the knowledge of a recent louse infestation in the patient's school's athletic team and an observation of several lice and egg casings in the scalp hair of the patient led to a diagnosis of head lice being rendered

Initial Treatment

  • Recommendations:
    • Permethrin 1% lotion applied for 10 minutes to clean, non-conditioned, towel-dried hair on Days 0, 7 and 15
    • Topical triamcinolone 0.1% lotion applied twice daily to the scalp and posterior neck to alleviate pruritus
  • Follow-up in 9 days

Follow-up evaluation strategy

9-day follow-up evaluation:

  • Several lice, eggs and nits noted, raising concern for permethrin resistance
  • Malathion 0.5% is prescribed (Day 0 with repeat application on Day 9)
  • Follow-up in 2 weeks
    • No evidence of lice infestation found

Further recommendations:

  • An alternative treatment schedule for topical benzyl alcohol, permethrin and pyrethrin application is on Days 0, 7 and 13 to 15 (total 3 applications), given that they are not ovicidal
  • Malathion 0.5% (Ovide) is a highly efficacious prescribed medication, killing 100% of mites and 98% of ova in 20 minutes. Application in a well-ventilated space is suggested, as it is a highly flammable product (78% isopropyl alcohol). It should be applied onto dry hair and allowed to dry without use of a hair dryer or other heat supply. If live lice persist, it should be reapplied in 9 days; however, malathion is highly effective after a single application
  • Benzyl alcohol 5% (Ulesfia) may be used in children over the age of 6 months. This prescribed medication is applied for 10 minutes then repeated 7 days later
  • Sulfamethoxazole/trimethoprim, in appropriate dose for body weight, for 2 weeks will kill head lice as it eradicates a symbiotic gastrointestinal bacteria that is essential for survival of the louse (for adults, this is one double-strength tablet twice daily). This treatment may be effective in situations in which topical applications have failed or where they are not possible or feasible. In patients allergic to sulfamethoxazole, trimethoprim alone can be used
  • Ivermectin (Stromectol), an oral anthelminthic agent, may be given in two doses of 200 µg each, separated by 10 days. It should only be used in children who weigh more than 15 kg
  • For patients 6 months of age and older, ivermectin (Sklice), a topical lotion (0.5%), may be administered as a one-time application to dry hair and scalp for 10 minutes, followed by a rinse out with water
  • Shaving the head will cure head lice. This is rarely necessary, but can be considered if acceptable to the child and parent

General discussion

Humans may be parasitized by three louse types: body lice, pubic lice and head lice - the latter being found on the hair of the scalp. Though not considered a serious threat to human health, louse infestation is contagious and can become a public health concern, especially when infestations affect school-age children, their caregivers and household members. It is important to note that the patterns of treatment resistance, especially to over-the-counter products, have emerged, thus the therapeutic strategies have shifted in recent years.

There is limited morbidity associated with lice. The primary concern is a hypersensitivity reaction to components of the louse saliva, which results in pruritus 4-6 weeks following the onset of the infestation. Notably, severe pruritus may result in excoriations with secondary skin infections such as impetigo.

The eggs of head lice are highly monomorphous ovoid structures that are firmly attached to the hair shaft via a white concretion such that they are challenging to remove. These are typically located close to the scalp (within millimeters) and may camouflage into the hair. The incubation time of head louse eggs ranges from 7-12 days, depending on heat exposure and weather. When empty, these egg casings are referred to as nits and are typically lighter in color and easier to visualize. Important diagnostic considerations are hair shaft casts (circumferential keratinous bands that easily slide up and down the hair shaft), seborrheic dermatitis (loose, greasy scale that is very loosely adherent to hair, if at all) and a superficial fungal infection of the hair shaft. It is important to note that the primary mode of transmission of hair lice is through direct contact with the head of an affected individual, though, rarely, may also occur through fomites such as hats and hairbrushes.

The lice, eggs or nits (empty egg casings) are not always obviously visualized. Important clues include excoriated erythematous papules (as shown in the image above) or macula cerulea (slate-blue macules) on areas of skin that come in contact with the hair.

Further reading

Frankowski BL, Bocchini JA Jr; Council on School Health and Committee on Infectious Diseases. Head lice. Pediatrics 2010;126:392-403.

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