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

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 

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