Scabies, Emergency Medicine

Basics

Description

Mites mate on skin surface and gravid female burrows into stratum corneum to lay eggs:
- Animal scabies can burrow but cannot reproduce on human hosts
Symptoms result from delayed type IV hypersensitivity reaction to mite, eggs, saliva, and feces:
- Inflammatory reaction leads to intense pruritus, which is the hallmark of the disease
- Crusted Norwegian scabies is characterized by large numbers of mites and is seen in the immunocompromised, disabled, and institutionalized:
  - More infectious than ordinary scabies due to high mite count
Despite >2,500-yr existence, an effective way to prevent scabies is still not known
Secondary infection is common and, as such, the morbidity associated with scabies may be underestimated
Scabies is a major global health problem in many crowded, resource-poor communities
Infestations become secondarily infected and epidemic acute poststreptococcal glomerulonephritis and rheumatic heart disease are often associated with endemic scabies

Scabies manifests itself in various forms in children and differs from that in adults:
- More inflammatory (vesicular or bullous)
- Involvement of face, scalp, palms, or soles
Highest prevalence is in children <2 yr old

Etiology

Epidemiology:
- Over the past 2 decades, the number of patients with scabies is increasing
- Up to 300 million cases yearly
- Burden of disease is highest in tropical countries
Produced by the human scabies mite, Sarcoptes scabiei var. hominis, or from animal mites
Transmitted by prolonged (15 " 20 min) direct skin-to-skin contact or, less commonly, by infested bedding or clothing:
- It is a disease of overcrowding and poverty, rather than a reflection of poor hygiene
- Probability of being infected is related to number of mites on infected person and length of contact
- Family members, sexual contacts, and institutional settings are at high risk for transmission
- Schools do not ordinarily provide the level of contact necessary for transmission
Mites subsist on a diet of dissolved human tissue (do not feed on blood) and can live up to 3 days off a hosts body
On average, the number of mites on a host at any time is ¢ ¼5 " 15:
- Main difference between crusted Norwegian scabies and ordinary scabies is the number of mites present on the host
- Patients with crusted Norwegian scabies are infected with thousands or up to a million mites

Diagnosis

Signs and Symptoms

Generalized and intense itching that is worse at night and usually spares the head and face
History

Site, severity, duration, and timing of itch
History should include family members and close contacts
Generalized, intensely pruritic eruption:
- Pruritus is intensified at night
Onset 10 " 30 days after exposure and infestation; reinfestation provokes immediate (within 1 " 3 days) pruritus:
- Patients with crusted Norwegian scabies are usually immunocompromised, have a decreased inflammatory response, and have less pruritus

Physical Exam

Often minimal cutaneous findings
Primary lesion: Linear, elevated, white-gray burrow (up to 1 cm long, width of a human hair) with small vesicle containing black dot at the end (mites barely visible to naked eye):
- Found symmetrically in web spaces of fingers, flexor surfaces of wrists and elbows, waistline, periumbilical skin, axillary folds, buttocks, penis, scrotum, vulva, and areola
- Head and neck rarely affected in adults but more commonly in infants and children
Secondary lesions: Inflammatory papules, nodules, excoriations, or secondary impetigo or folliculitis seen on back, shoulders, axilla, waist, buttocks, and flexor aspects of elbows:
- Secondary lesions are usually more numerous and prominent than burrows but also may be few if topical steroids used
Longstanding infestation results in chronic excoriation, eczematization, and hyperpigmented and lichenified skin
Crusted Norwegian scabies produces gross scaling with hyperkeratotic plaques on hands, feet, scalp, and pressure-bearing areas:
- Scales can become warty
- Fissures may appear
- Nail involvement is common
Genitalia should be examined in all instances of suspected scabies

Eruption may be seen from head to toe
Vesicles are often found in infants due to their predisposition for vesicle formation
Neonatal scabies is associated with poor feeding, poor weight gain, and super infection

Essential Workup

Careful history and skin exam for characteristic lesions
The diagnosis is easily missed and should be considered in any patient with persistent generalized pruritus
Factors related to missed diagnosis in patients admitted through the ED:
- Overcrowding, time constraints, and lower patient illness severity scores

Diagnosis Tests & Interpretation

Lab

May be indicated in immunocompromised patients or in patients with systemic infection:
- Elevated IgE and IgG and peripheral eosinophilia can be seen in crusted scabies
New diagnostic lab studies are being developed (circulating IgE levels, PCR, ELISA, and DNA finger printing)
When endemic, empiric treatment may be more cost effective than lab testing
Consider screening for other STDs

Imaging
Epiluminescence microscopy and noncomputed dermoscopy are noninvasive, simple, accurate, and rapid imaging techniques
Diagnostic Procedures/Surgery

Scrape skin at burrows or under fingernails with no. 15 blade and mineral oil (adheres scraped material to blade) and observe under low-power microscope for mites, eggs, or fecal material; may be operator dependent
A negative scraping does not exclude infestation due to low number of mites in classic scabies:
- Sensitivity <50% and is affected by number of sites sampled and samplers experience
Skin biopsy may confirm diagnosis but findings may also be absent and reveal only a delayed hypersensitivity reaction

Differential Diagnosis

Atopic dermatitis
Eczema
Dermatitis herpetiformis
Papular urticaria
Folliculitis
Lichen planus
Pruritic urticarial papules and plaques of pregnancy
Adult linear IgA bullous dermatosis
Syphilis
Pediculosis
Pityriasis rosea
Impetigo
Seborrheic dermatitis
Flea bites and bedbugs

Treatment

Pre-Hospital

Maintain universal precautions.

Initial Stabilization/Therapy

No specific stabilization necessary
ED is an important route for admission to the hospital and detecting infested patients early can be achieved by screening for high risk patients

Ed Treatment/Procedures

Treatment should not be empiric for patients with generalized itching but reserved for patients with a history of exposure, a typical eruption in a characteristic distribution, or both
Treat patient and all persons in immediate contact with topical scabicide:
- Treat all contacts at the same time, regardless of the presence of symptoms
Permethrin 5% is 89 " 92% effective, and is well tolerated (category B pregnancy):
- <2% of permethrin is absorbed into the skin, making its potential toxicity low:
  - For children ≥2 mo older
  - Massage from head to toe (avoid eyes and mouth) and remove in shower 8 " 14 hr later
  - Repeat 2nd application in 1 " 2 wk time
Crotamiton 10% is 50 " 60% effective and used when other scabicides are not tolerated
Ivermectin administered orally for 2 doses 7 " 14 days apart has shown similar efficacy as permethrin (but not used in pregnant or lactating women or children <15 kg):
- Effective in patients unable to tolerate topical scabietics or in patients with resistant or crusted Norwegian scabies
- May not be effective against all stages of life cycle (may not sterilize scabies eggs)
Lindane 1% may be slightly less effective and is potentially toxic to the CNS:
- Lindane absorption (through skin, lung or intestinal mucosa, or mucous membranes) is about 10%
- Side effects include nausea, headache, vertigo, amblyopia, irritability, and seizure
- Do not use in pediatric patients or patients with extensive excoriations or dermatitis
Sulfur is the oldest known treatment of scabies, and is the drug of choice for infants <2 mo and for pregnant or lactating women
Crusted Norwegian scabies 1st requires removal of hyperkeratotic scale with keratolytic to facilitate entry of the scabicide
Treatment failures:
- Treatment failures are frequent in crusted Norwegian scabies, and use of multiple agents including oral medications is often necessary
- Machine wash and dry in hot cycles (60 °C) or dry clean all clothes and bedding worn within 2 days of treatment or place items in plastic bags for 3 days
- Vacuum household floors, carpets, mattresses, and furniture
- Autoclaving, bleaching, or fumigation are not indicated
- Emphasize that itching may continue for 1 " 4 wk after mites are killed due to skin inflammatory reaction
- Topical steroids and oral antihistamines can reduce pruritic symptoms
- Relapses can occur from untreated areas such as the scalp and subungual regions
- Treatment failures tend to arise from poor patient understanding and inadequate patient education

Medication

Scabicides:
- Crotamiton 10% lotion or cream: Apply topically from neck down in adults and entire skin surface in children QHS for 2 nights, then rinse off 48 hr after last application
- Ivermectin 3 mg tablets: 1st PO dose of 200 ¼g/kg should be followed by 2nd PO dose of 200 ¼g/kg 7 " 14 days later (pregnancy category C). Take with food
- Lindane 1% lotion or cream: Apply topically from neck down and rinse off after 8 " 12 hr; contraindicated in infants, pregnancy, lactation, excessive excoriations, or seizure disorder
- Permethrin 5% cream (Elimite): Apply topically from neck down in adults and entire skin in children QHS; rinse off after 8 " 14 hr (pregnancy class B, unknown safety in breast-feeding)
- Sulfur 5 " 10% precipitated in petrolatum: Apply topically nightly for 3 consecutive nights and then wash off 24 hr later
Antipruritics:
- Low sedating/selective antihistamines:
  - Cetirizine (Zyrtec): Adults and peds >6 yr: 5 " 10 mg/d PO; 6 " 12 mo: 2.5 mg/d PO; 12 " 24 mo: 2.5 mg/d PO to BID; 2 " 6 yr: 2.5 " 5 mg/d PO
  - Fexofenadine (Allegra): Adult and peds >12 yr: 180 mg/d PO or 60 mg PO BID; 6 mo " 5 yr: 15 " 30 mg PO BID; 6 " 11 yr: 30 mg PO BID
  - Loratadine (Claritin): Adults and peds >6 yr: 10 mg/d PO; 2 " 5 yr: 5 mg/d PO
- Sedating/nonselective antihistamines:
  - Diphenhydramine (Benadryl): Adults and peds >12 yr: 25 " 50 mg PO q4 " 6h; 2 " 6 yr: 6.25 mg PO q4 " 6h; 6 " 12 yr: 12.5 " 25 mg PO q4 " 6h
  - Doxepin: 25 " 50 mg PO BID, peds: Dosing currently unavailable
  - Hydroxyzine HCl (Atarax): Adults and peds >12 yr: 25 " 100 mg PO q6 " 8h; <6 yr: 2 mg/kg/d PO div. q6 " 8h; 6 " 12 yr: 12.5 " 25 mg PO q6 " 8h

First Line
Permethrin 5% cream
Second Line
PO Ivermectin or Crotamiton 10% lotion or cream

Follow-Up

Disposition

Admission Criteria

Patients with severe topical or systemic super infection
Refractory or relapsing cases

Discharge Criteria
Nontoxic appearing patients with routine symptoms

Followup Recommendations

Re-evaluate after 1 " 4 wk for recurrence:

Itching may persist for up to 4 wk after correctly applied therapy
Treatment failure is often due to incorrect application of topical agents or due to failure to treat all contacts
Retreat if live mites are found

Pearls and Pitfalls

Scabies is a common parasitic infection that is transmitted by prolonged direct skin-to-skin contact
Scabies in children can differ from that in adults
Crusted Norwegian scabies is characterized by a large number of mites, and is seen in immunocompromised or institutionalized patients
Treatment failure is common:
- Proper patient education can decrease treatment failures.

Additional Reading

Chosidow O. Clinical practices. Scabies. N Engl J Med. 2006;354:1718 " 1727.
Currie BJ, McCarthy JS. Permethrin and ivermectin for scabies. N Engl J Med. 2010;362:717 " 725.
Hong MY, Lee CC, Chuang MC, et al. Factors related to missed diagnosis of incidental scabies infestations in patients admitted through the emergency department to inpatient services. Acad Emerg Med. 2010;17:958 " 964.
Leone PA. Scabies and pediculosis pubis: An update of treatment regimens and general review. Clin Infect Dis. 2007;44(suppl 3):S153 " S159.
Scabies. Atlanta: Centers for Disease Control and Prevention, 2008. Accessed at http://www.cdc.gov/scabies/.
Strong M, Johnstone P. Interventions for treating scabies. Cochrane Database Syst Rev. 2007;(3):CD000320.

Codes

ICD9

133.0 Scabies

ICD10

B86 Scabies

SNOMED

128869009 Infestation by Sarcoptes scabiei var hominis (disorder)
128870005 Crusted scabies (disorder)

Home

Erectile Dysfunction

Doctor123.org