scabies
SCABIES
Scabies is a contagious disease caused by the mite Sarcoptes scabiei var hominis.
The affected individual usually complains of having a highly pruritic rash that occurs at night.
It occurs more often in children <15 years of age, sexually active young adults, the immunocompromised and in persons living in crowded living conditions (eg nursing homes, military barracks).
Transmission is typically by direct skin contact with an infected person and in adults, sexual transmission is common.

Classification

Primary Lesions

  • Burrows
    • Patient may have linear, curved or S-shaped silvery lined burrows w/ a mean length of 0.5 cm
    • Burrows & other primary lesions may not be seen because they may have been destroyed by scratching
    • Usually found on the finger webs, sides of the hands & feet, wrists, buttocks, penis or scrotum
    • In the infant: Usually found on the palms & soles
    • May enhance the sighting of burrows w/ blue or black fountain ink because the burrow absorbs the ink & is highlighted as a dark line
  • Vesicles & Papules
    • Isolated pinpoint vesicles which are filled w/ serous fluid may be present
    • Papules may be from a hypersensitivity reaction & rarely contain mites
    • Most commonly found on the finger webs
    • In the infant: Vesicles or pustules may be found on the palms & soles

Secondary Lesions

  • Often predominate the clinical picture as they are a result of infection or scratching
  • Pinpoint erosions are the most common secondary lesions
  • Pustules are a sign of secondary infection
  • Scaling, erythema & eczematous inflammation can occur due to excoriation or irritation

Distribution of Lesions

  • Adults & older children
    • Typically occur from the neck down: The interdigital web spaces of the hands, the flexor surface of the forearms (wrist & elbow), axillary folds, umbilicus & belt line, buttocks, ankles, groin, penis, scrotum, areola & nipples
    • Scalp & face are usually not infected in the adult
  • Infants
    • Lesions are usually distributed on the palms & soles, & occasionally on the face & scalp

Laboratory Tests

Diagnostic tests

Microscopic Identification

  • Diagnosis is confirmed by microscopic identification of the mites, eggs or mite feces
  • Specimen should be taken by scrapping the burrows or the newest lesions w/o excoriations & eczematization
    • A drop of mineral oil should be placed on the lesion & then scraped w/ a sterile #15 surgical blade & may be viewed directly under a light microscope
    • 10% KOH soln may be used to decrease the amt of keratinic debris which is helpful when diagnosing crusted scabies
    • Dermoscopy may be used as a guide for procurement of skin samples
  • When skin specimens are negative but a strong clinical suspicion remains, a successful trial of scabicide therapy may confirm the diagnosis 

Diagnosis

Nodular Scabies

Clinical Presentation

  • Red-brown nodules that are few in number but are extremely pruritic
  • Most often lesions are found on covered areas (eg axillary, groin & male genitalia)
  • Mites are typically absent from these lesions
  • Probably represent an exaggerated inflammatory response to the mite or its products
  • May persist long after successful treatment & may require intralesional corticosteroid inj

Crusted (Norwegian) Scabies

  • Highly contagious form of scabies w/ the affected person being infested w/ hundreds to millions of mites

Clinical Presentation

  • Typically occurs in immunocompromised patients & in patients w/ severe systemic illness, neurologic/mental disorders or in residents of long-term care facilities
  • Itching may be absent or severe
  • Patients may present w/ hyperkeratotic crusted plaques which may be generalized or localized to the hands or feet
  • Occasionally patients may have psoriasiform or eczematous lesions w/ fine, powder-like, red, scaling eruptions on the face, neck, scalp & trunk
  • In some cases, generalized lymphadenopathy & eosinophilia are present

Microscopic Identification

  • Diagnosis is made by direct microscopy of skin samples w/ mineral oil or KOH that shows large numbers of mites & eggs in the scales
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