DISCUSSION
This case nicely illustrates several issues revolving around the diagnosis of scabies. One might think this would be a simple matter: Diagnose, then treat. Alas, it is seldom so.
For one thing, the diagnosis of scabies needs to be confirmed, whenever possible, with microscopic findings of scabetic elements. Without this, patient and provider confidence are lacking—a situation that often leads to shotgun treatment.
In addition, had the diagnosis been confirmed prior to presentation to dermatology, the previously consulted providers might have considered treating the whole family and trying to identify the source of the infestation. Both of these are absolutely crucial to successful treatment.
Several factors make the diagnosis of scabies difficult in infants. Any part of an infant’s thin, soft, relatively hairless skin is fair game (whereas, in adults, scabies rarely affects skin above the neck). Furthermore, although infants with scabies undoubtedly itch—probably just as much as adults—they are totally inept excoriators and even worse historians. In contrast, adults with scabies will scratch continuously while in the exam room and complain bitterly 24/7.
Once the diagnosis is established, a crucial element of dealing effectively with scabies is education—in this case, of the parents. They must understand the nature of the problem in specific terms. For example, scabies cannot be caught from or given to nonhuman hosts (eg, animals). And while I advise affected families to clean areas such as beds, sofas, and bathrooms, I also emphasize that the organism does not reside in or multiply on inanimate objects. Despite my best efforts, though, some families become almost hysterical: steam-cleaning every surface, calling pest control, washing bedding and towels multiple times, and calling me three times a day.
Families must also understand that treatment of all household members must be coordinated and done twice, seven to 10 days apart, in order to kill freshly hatched organisms. This child was treated with permethrin 5% cream, applied to the entire body and left on overnight, then washed off the next morning (twice per the schedule outlined above). In addition to permethrin, the adults were treated with ivermectin (200 mcg/kg) on the same schedule. Even with these extensive measures, recurrence would not be surprising.
Most often, when treatment “fails,” it is because the diagnosis was not scabies in the first place. In confirmed cases, treatment will be unsuccessful if all family members are not adequately (and concurrently) treated. Another problem occurs when the actual source is outside the home (daycare, sleepovers, sexual partner) and remains unidentified—dooming the family to recurrence. (Institutional scabies—from nursing homes, group living, etc—can be far more difficult to deal with and is beyond the scope of this article.)
The differential for scabies includes—most significantly—atopic dermatitis, which it can closely resemble.
TAKE-HOME LEARNING POINTS
• Scabies can show up almost anywhere on an infant’s body, because the skin is so thin, hairless, and soft.
• If the baby has scabies, chances are the parents and siblings have it too.
• Someone brings scabies into the family, and unless the source is identified and treated, the problem will recur.
• Microscopic examination (KOH) for scabetic elements is a crucial component of diagnosis and treatment.
• Scabies sarcoptes var humani is species-specific and cannot be given to or caught from an animal.
• Permethrin cream 5% is considered safe for infants ages 2 months and older.