Clinical features

Common presenting lesions in scabies are papules, vesicles, pustules, and nodules (1).

Classically, greyish white linear burrows may be seen on the finger webs, sides of the fingers, wrists, elbows, anterior axillary fold, periumbilical area, and areolae.

Burrows are rarely seen on the buttocks and male genitalia - instead, there are firm, red papules.

Scabies is characterised by severe and persistent itching, often worse at night and following bathing, is frequently the initial complaint - this indicates that hypersensitivity has developed and may antedate infection by several weeks - often, there is a widespread rash with many small papules, but there may be excoriation, dermatitis, and secondary infection with vesicles and pustules (1).

In the first attack the incubation period is 2-6 weeks but is much shorter in subsequent attacks - possibly as short as 24-48 hours (1).

Clinical presentation may vary according to the age of the patient:

• in adults and older children - burrows are frequently seen in interdigital web spaces, wrists, anterior axillary folds, peri-areolar region of the breasts in women. In adults burrows are uncommon on the trunk (1)
• in infants and young children - affects non-hair-bearing areas on palms and soles of the feet, behind the ears, on the face, head, neck and scalp. In infants scabies infestation commonly presents as papules and vesicopustuler lesions. In babies, pink-brown nodules are particularly characteristic sign of scabies (1). Scabies is rarely seen in children less than 2 months of age
• in the elderly - burrows are commonly seen on the palms and soles and may be numerous. Papulosquamous lesions on the trunk, frequently surmounted by burrows are common. Often troublesome secondary eczematization can occur. In some cases mild to severe eczematous changes can be the predominant clinical feature (1)

In infants and young children atypical distribution of lesions (vesicles, pustules and nodules) can be observed. Due to the occurrence of eczematization and impetigo, scabies may be confused with atopic dermatitis (2).

Severe and extensive secondary infection can occur in untreated scabies which may lead to cellulitis, folliculitis, boils, impetigo, or lymphangitis (1).

In immunocompromised people, scabies mites can also infect the face, neck, scalp, and ears (1)

Atypical clinical presentations can occur (1):

• a bullous pemphigoid-like reaction may occur
• in people taking steroids the rash may be atypical (scabies incognito)
• rarely, scabies may present as cutaneous vasculitis (e.g. with a purpuric rash and areas of cutaneous infarction)
• in infants, children, the elderly, and in people with immunodeficiency syndromes scabies may occur together with seborrhoeic dermatitis of the scalp or may simulate the disease (1)

Reference:

• 1. Drug and Therapeutics Bulletin (2002), 40 (6), 43-6.
• 2. Oliver Chosidow. Scabies. N Engl J Med 2006;354:1718-1727
• 3. Clinical knowledge summaries 2007. Scabies