DERM 04 and 05: Scabies Flashcards
(21 cards)
Describe the pathophysiology of scabies.
in stratum corneum
Describe the method of transmission of scabies.
- highly contagious
- transmission results from direct skin-to-skin contact – may take 4-6 weeks to develop symptoms/signs after initial exposure (clinically latent period)
- lives up to 3 days off human host at room temperature – may survive up to 19 days in cool, humid environment, ability to infect host decreases with time off host
- infestation may be endemic in impoverished communities or nursing homes, hospitals
What are the 3 forms of scabies?
- classic
- nodular
- crusted (Norwegian)
What is the classic form of scabies?
- most common
- average parasite burden: 10-12 mites in first 3 months
- adults: erythematous papular rash, burrows
What is the nodular form of scabies?
- from an exaggerated hypersensitivity reaction
- pruritic reddish-brown nodules on genitalia, buttocks, groin, axillae
What is the crusted (Norwegian) form of scabies?
- hyperinfection – often occurring in immunocompromised patients (AIDS, lymphoma, elderly in nursing homes)
- thickened, malodorous skin patches (particularly scalp, hands, feet)
- only 50% of patients report itching
- 100,000s of mites
- highly infectious – higher death rates from 2° bacterial infection leading to sepsis
What do the lesions of scabies look like?
- white-silvery linear or S-shaped burrows with inflammation/papules/vesicles/scales
- 3-4 mm crusted lesions on skin folds
- excoriations and crusted lesions clustered around crease of wrist
- pruritic, pustular rash in webbing between fingers
- interdigital scaling in first web space of hand
- interdigital scale, crusting, and burrow on hand
What are the pruritic signs and symptoms of scabies?
3-10 weeks later (in primary infection), intense itching occurs (may infect others during this asymptomatic period)
- particularly intense at night
- subsequent exposures result in immediate itching (within 48 hrs)
- skin lesions due to both burrows of mites and widespread inflammatory response in skin caused by hypersensitivity to mites and their saliva and excretions
- adult mites burrow into skin of host, mate, females lay eggs, larvae hatch and life cycle repeats
- itching can persist for weeks after mites are eradicated
What can occur after primary infection of scabies?
secondary bacterial infections may occur and may require use of prescription topical antibiotics
What are the commonly affected areas of scabies?
- classic: web spaces of fingers, front of wrists, sides of hands and feet, back of elbows, skin folds, underarms, breasts, groin, abdomen, back (rarely above neck)
- atypical: scalp (usually young children, elderly), may be head-to-toe in children < 3 years old (vesicles, pustules), particularly scalp, hands, feet, body folds
What information should be gathered for diagnosing scabies?
- on what areas of body are lesions mostly seen
- any itching – specific time that it occurs most
- any family or friends with similar symptoms
Describe diagnosis and referral for scabies.
- have low threshold for referral for patient presenting with itchy (particularly at night) rash of unknown origin – especially if other close contacts have similar symptoms
- diagnosis should be made/confirmed by physician (dermatologist) – extensive differential diagnosis, difficulty in differentiating between active infestation/residual skin reaction/reinfestation
What are the goals of therapy for scabies?
- eradicate scabies mites
- relieve symptoms of pruritis
- prevent complications (secondary bacterial infections)
- prevent spread of infestation
- prevent reinfestation
What are the non-pharmacological treatments for scabies?
- clean: wash all clothes and linens in hot water followed by hot dryer, vacuum furniture and mattresses, particularly bedroom floors, store other objects in sealed bags for at least 2 days (up to 3 weeks if desired)
- cool compress x 20 mins on severely itchy areas
- avoid body contact with others until full treatment cycle completed
Who should be treated for scabies?
all contacts of person with scabies (even if asymptomatic) require treatment – sexual, close personal (friends, co-workers), or household contacts within the preceding month
What is the drug of choice for scabies treatment?
permethrin 5% (Kwellada-P Lotion, Nix Dermal Cream) – schedule 2
- drug of choice in adults and children > 3 months old
Permethrin 5% (Kwellada-P Lotion, Nix Dermal Cream)
- massage into all skin areas (adults, older children apply to entire body from neck down unless evidence of scalp involvement), leave for 8-14 hours (usually applied overnight) then wash off
- one treatment may be adequate, but recommend second application 7-10 days as mechanism of action is not ovicidal, especially if live mites can be found and new lesions appear
- treatment for atypical scabies, younger children, elderly: apply to entire skin surface except around eyes
- adverse effects: pruritis, edema, erythema
- resistance of scabies to permethrin is rare
- contraindicated in patients allergic to chrysanthemums
- recommended during pregnancy and breastfeeding
What are the second-line agents for scabies treatment?
there is no most effective second-line agent
- crotamiton 10% – schedule 2
- sulfur 5-10% – in paraffin or petroleum jelly
- ivermectin – NOT in Canada
Crotamiton 10%
- schedule 2
- reduces itch via counterirritant, cooling effect
- less effective than permethrin
- less effective at reducing persistent itch
- resistance reported
Sulfur 5-10%
- in paraffin or petroleum jelly
- low risk of toxicity for infants, usually reserved for < 2 months old
- limited evidence of efficacy (general antiparasitic effect)
- odourous and messy application
Ivermectin
- topical: similar efficacy – NOT indicated for scabies in Canada
- oral: used when treatment failure with topical scabicides, in epidemic settings for bedridden patients, immunocompromised with Norwegian scabies – NOT indicated for scabies in Canada
