Scabies burrows

Diagnosis

Itchy skin disorder caused by
infestation with scabies parasite

Epidemiology

Pathophysiology

Risk factors

Infection
Parasite (scarcoptes scabeii) burrows into epidermis through the stratum corneum, lays eggs and dies
Immune response to the mites and saliva/eggs/faeces causes the itching
Spread by skin-skin contact, often sexually
Incubation period 3-6wk; mites can survive away from host for up to 7 days

Hyperinfection
Crusted scabies, caused by hundreds/millions of mites
in exfoliating scales
Immunocompromised host

F>M

Teens (10-19y)

Low SEC

Crowded living conditions

Institutionalisation

Contact with infested person

Immunocompromised (crusted scabies)

Female

Clinical
presentation

Diagnosis

Management

Complications

Prognosis

Secondary bacterial infection
S aureus, GAS - impetigo, folliculitis, furunculosis, abscess

Secondary eczematisation
Due to scratching and irritant meds

Nodular scabies
Pruritic nodules in axilla and groin
(prolonged immune response to mite antigens)

Sepsis
Risk in crusted scabies

Often resolves quickly with treatment

Itching may continue for 2wk after treatment

Itching
(worse at night)

Linear burrows
Wavy, thready, white/grey lines,
small vesicle with black dot at end;
fingers and wrists
linear burrows

Erythematous papules/vesicles/pustules
Interdigital spaces, sides of fingers,
wrists, elbows, axilla, genital area
scabies papule

Violet nodules
Groin, buttocks, axilla
Pruritic
scabies nodule

Examination

Investigation

History

DH
Current meds (immunosuppressants),
allergies

FH
Others affected

SH
Living conditions, smoking, alcohol
Sexual contact/history

PMH
Other medical conditions, immunocompromised

PC/HPC
Site, onset, character (itchy, red, scaly, nodules, papules),
systemic symptoms, red flags, others affected

Dermatological
Linear burrows, erythematous papules, nodules,
crusted scabies

Bedside
Ink burrow test: blue/black ink to papule, removed with alcohol;
+ve test = dark zigzag line running away from lesion (mite burrow)

Biopsy
Skin scrapings for microscopy (parasites, eggs, faeces)
High specificity but low sensitivity

Medical

Conservative
Information and advice
Partner/family notification and treatment
Hygeine advice (thorough scrubbing and drying after washing, avoid close contact, sharing towels etc.)
Hot wash of bedding, clothing towels
Referral to specialist/admission if crusted scabies,
young children <2m old, or nodular scabies

Topical insecticide
Indication: uncomplicated scables
E.g. permethrin 5% cream, malathion 0.5% cream
MOA: apply to whole body from chin downwards, special attention to affected areas, kills parasite, wash off after 8-12h
Second application 1 week later

Anti-pruritic
Indication: post-scabies itch
E.g. crotamiton 10% cream
MOA: antiparasitic and antipruritic

Antihistamine
Indication: nighttime itching
E.g. chlorphenamine PO nocte
MOA: reduces itch by inhibiting histamine release,
also sedative to aid sleep

Steroids
Indication: nodular scabies
E.g. topical or PO
MOA: reduces inflammation, reducing nodules

Oral insecticide
Indication: severe scabies
E.g. PO ivermectin