Discussion

Crusted scabies, previously known as “Norwegian” scabies, is a rare and severe form of scabies less frequent in children compared with adults. 3 It is characterized by large, crusted lesions, generalized scales, and thick hyperkeratosis. 4 While hands and feet are most affected, the most severe cases have near total body surface involvement. 5 There is a delay of diagnosis per the literature from 2 to 18 months.6,7 Diagnosis can be based on clinical presentation, history, and physical exam, and can be confirmed with skin scrapings or skin biopsy. 8 Without adequate treatment, secondary infections can lead to bacteremia or sepsis. 1 Our patient had MSSA and S. marcescens bacteremia. Staphylococcal and streptococcal infections 9 are the most common organisms with bacteremia/sepsis being reported in 8.8% of the cases. 10 Treatment of MSSA bacteremia consists of a beta-lactam agent such as nafcillin, oxacillin, flucloxacillin, or cefazolin, 11 with our patient receiving nafcillin. Empiric treatment for methicillin-resistant Staphylococcus aureus (MRSA), which is another common bacteria causing bacteremia consists of vancomycin. 12 Serratia marcescens is a rare secondary infection from scabies with only one report of a wound culture being positive with S. marcescens, 13 but there are no reports on S. marcescens bacteremia. Serratia marcescens bacteremia is usually treated with fluoroquinolones, aminoglycosides, trimethoprim-sulfamethoxazole, piperacillin-tazobactam, third- and fourth-generation cephalosporins, aztreonam, and carbapenems 14 with our patient receiving a third-generation cephalosporins.

Our patient had Down syndrome that has been associated with CS8,10,15 and felt to be due to an immune dysfunction 16 or lack of response to a pruritic rash.10,16 Most individuals with healthy immune systems can mount effective responses against the scabies mite. 17 Mechanical debridement of mites and eggs via scratching is an effective mechanism to limit proliferation but patients with cognitive impairment who are unable to interpret the itch or unable to scratch are at increased risk of developing CS. 8 In addition, Down syndrome patients are thought to have an immunodeficiency with a significant decrease in switched memory B and T cells.15,18 Also, there is an elevated baseline cytokine level prior to any induced inflammation. 19

Systemic and topical corticosteroids have been associated with CS. Locally applied corticosteroids (especially fluorinated) alter the skin’s immune system, with the inflammatory and cellular response reduced. 19 In addition, systemic steroids can decrease the pruritic symptoms and immune response allowing the mites to proliferate and develop into CS. From the literature, children with CS, have a prevalence of prior corticosteroid use of 75%. 20 Our patient received both systemic and topical steroids.

This is the first report of a pediatric patient with autism having CS. Autism by itself has been associated with dysfunction in B, T and NK cells and increased production of cytokines and auto-antibodies.21,22 In Down syndrome and autism, there is an elevated baseline level of cytokines, but how exactly it is related to immune dysfunction is speculative.21,23 One theory is that there is a cytokine storm when the body is induced with more inflammation such as with a virus that leads to a decrease in antibacterial defenses. 22 Instead of a virus perhaps scabies induced more inflammation, which led to this cytokine storm with decreased antibacterial defenses leading to bacteremia in our patient.

The treatment for CS is more intense than classic scabies. An approach to the patient with CS is to initiate combination treatment with topical permethrin and oral ivermectin and treatment of the pruritus. This combination of topical scabicide (permethrin) and oral ivermectin has been shown to be effective.24-27 The use of lindane is contraindicated for CS due to the risk for toxicity. 28 For the pruritus associated with the rash can be treated with oral antihistamines such as hydroxyzine and diphenhydramine. Opinions vary on the use of topical corticosteroid therapy. A complication of CS is secondary bacterial infection where treatment is geared toward staphylococcal and streptococcal infections. Hospitalization is recommended for secondary bacterial infections and may be indicated for moderate to severe pain 29 or severe rash. 30