Management of scabies

Clinical manifestations

The two major clinical variants of scabies are classic scabies and crusted scabies. Symptoms typically appear 2–6 weeks after infestation. Classic scabies (Fig. 1), the most common presentation, is associated with a relatively low mite burden of approximately 10–15 mites on the body. Crusted scabies (Fig. 2), on the other hand, usually occurs in older or immunocompromised individuals and is associated with a higher mite burden (up to millions of mites on the body).(4) It is also more often seen in disabled and institutionalised patients. This infestation often presents as generalised dermatitis with crusted hyperkeratoses on the palms, soles, under the fingernails, and on the ears, trunks and extremities. Pruritus may be minimal or absent, or the host may be physically incapable of scratching.(5)

Fig. 1

Photograph shows numerous erythematous papules on (a) the fingers and web spaces and (b) axilla of a patient with classic scabies.

Fig. 2

Photograph shows hyperkeratotic crusts on the fingers and palms in a nursing home patient with crusted scabies.

The salient features of classic scabies are intense itch, erythematous papules and excoriations, typical distribution, and a contact history of patients with scabies. The usual distribution is: the interdigital web space of the fingers, the insides of wrists and on the inner elbow; the soles of the feet; around the breasts and axillae; the male genitalia, especially the scrotal and penile areas; and on the buttocks, knees and shoulder blades.(6) In children, common sites of infestation are the scalp, face and neck, and palms and soles.

Making the diagnosis

The combination of visual inspection, noting the characteristic pruritic lesions and their distribution, together with contact history enables the primary care practitioners to make a confident diagnosis of scabies. Differential diagnoses include other pruritic conditions such as drug eruptions, eczema, lichen planus and other infestations such as hemiptera (bedbugs). Apart from the symptomatology, other salient points in history-taking include a detailed drug history. Eczema may present at the flexures, while classical lichen planus tends to affect the volar aspects of wrists and ankles as well as the anterior aspects of the knees. As for scabies, areas affected include the interdigital web space of the fingers and the sides of the hands. The wrists, elbows, axillae, groin, breasts and feet are the other commonly affected sites (Fig. 3). A skin scrape can be taken at non-excoriated areas or non-inflamed areas where there are burrows and a pimple-like rash.

Fig. 3

Photomicrograph of an adult Sarcoptes scabiei.

Early recognition and treatment

When asking a patient about number of household members, physicians are reminded to specifically ask if there were domestic helpers or grandparents living together or staying intermittently up to six weeks prior to the presentation. Patient and family members should be informed that although scabies infestation is relatively benign, it is highly transmissible. Therefore, the principles of treatment (Box 1) should be carried out diligently. Table I shows the treatment regime for each patient group.(7,8)

Box 1

Principles of treatment in household, community and institution facilities:

Table I

Medical treatment for scabies.(7,8)

In nursing homes and institutions, early recognition of crusted scabies is essential to prevent outbreaks.(9) Once an outbreak occurs, prompt control of the index patient and rapid tracing of contacts to identify secondary cases are necessary. When prolonged exposure to a case of crusted scabies results in multiple secondary cases, the most efficient strategy for terminating the outbreak is the institution of simultaneous mass prophylaxis, which can be implemented without ward closure.

It is important to recognise that itching may persist or even worsen for some time after applying the medication. These steps may give patients some relief from itching:(10)

1. Cool and soak the skin by using a cool, wet washcloth on irritated areas of the skin.

2. Apply a soothing lotion such as calamine lotion.

3. If the itching is severe, consider antihistamines to relieve the itching and skin irritation. Non-sedative antihistamines appear to be as effective as sedating histamines.

4. After eradication of mites, medium-potency topical corticosteroids (in age-appropriate patients) can also be used to control itching for 1–2 weeks, especially for scabetic nodules.(5)

Scabies may result in secondary skin infections leading to boils, cellulitis or lymphangitis due to Streptococcus pyogenes (S. pyogenes). Streptococci and staphylococci have been isolated from skin burrows as well as mite faecal pellets, suggesting that the mites themselves may contribute to the spread of pathogenic bacteria.(11) Secondary infection of scabies with S. pyogenes is a major precipitant of acute post-streptococcal glomerulonephritis and possibly rheumatic fever.(12)