Specific History

Onset

Human scabies is an infestation caused by an organism named Sarcoptes scabiei var. hominis, an obligate human parasite. The disease is most common in schoolchildren and young adults, but may be seen in all age groups and is also common in nursing home settings. Within family units, it is not unusual for the presenting case to be quite removed from the index case that brought the disease into the family. History of overnight house guests, school contacts, or close friends with symptoms is important, especially when one cannot obtain firm laboratory confirmation. Cases seen from skilled care facilities should trigger an investigation into other patients or staff with pruritus or dermatitis. When seeking this history, remember that the exposure occurred at least 1 month prior to the time the patient became symptomatic. Initial symptoms consist of discrete lesions, often on the wrists and hands, but these are frequently overlooked. Progressive pruritus, which interrupts sleep and normal activity, is what usually prompts the victim to seek help. The presence of the primary lesions is often elicited only by direct questioning. Some patients present late with extensive secondary changes. These consist of widespread dermatitis, secondary bacterial infection, and self-induced dermatitis caused by inappropriate attempts at treatment. It is estimated that the average victim has the infection for at least a month before generalized discomfort begins. Scabies should be considered in the differential of any generalized pruritic disorder. A special form called "crusted" or "Norwegian" scabies can present with minimal or no itching.

Evolution of Disease Process

Scabies begins insidiously with small comma-shaped burrows or tracks that, when viewed with magnification, have a scale at one end and a tiny papule or vesicle at the other end. The vesicle end is where the female mite is located. These lesions are initially asymptomatic and gradually increase in number. In adults, the wrists, finger webs, and lateral fingers are the most common areas. Adult men often show characteristic lesions on the genitalia, probably from autoinoculation. Adult women sometimes show characteristic lesions on the areolae or palms. Preschool children often have tracks on the palms, soles, and the lateral margins of the feet. About 4 to 6 weeks after infestation, the average patient begins to develop an immune response to the organism and the lesions become increasingly pruritic. Scratching destroys many burrows and limits but does not eradicate the infection. With persisting infestation, most victims develop an immune response that produces generalized itching, widespread papular dermatitis, and dermographism. Later, chronic generalized eczematous dermatitis and secondary impetiginization can occur. Even after successful treatment, persons with these intense immune reactions may take several weeks to become asymptomatic and inflammatory lesions may persist for weeks or months even though the organisms are no longer viable.

Persons who are immunosuppressed, physically unable to scratch, or have neurologic deficits that abolish itching, develop crusted (Norwegian) scabies. Itching may be minimal or absent and they present with thick keratotic crusted lesions of the hands, nails, elbows, knees, and ankles which may gradually progress to an erythroderma. These patients teem with organisms, are highly contagious, and may show generalized lym-phadenopathy.

Evolution of Skin Lesions

The typical track lesions remain discrete and may become more erythematous or inflammatory as the immune response intensifies. This is particularly true with lesions in the genital regions. With established scabies, resolving tracks and new active tracks will be found interspersed in the same areas.

Provoking Factors

Overcrowding, poor hygiene, and close physical contact such as handholding or shared sleeping arrangements foster spread. Nursing facilities are also prone to outbreaks because of crowding and the presence of a population of patients more likely to develop the highly contagious crusted variety.

Self-Medication

Self-treatment is a significant problem in scabies cases both before and after the diagnosis is established. Because of the intense itching, victims often will try OTC remedies such as steroid creams or harsh remedies that give short-term relief by coun-terirritant effects. This misguided treatment either spreads the infestation or causes severe drying, which in turn worsens the pruritus. It is essential to take control of general skin care and help the patient understand that inappropriate treatment is making matters worse. After diagnosis, patients with established scabies will continue to expe rience symptoms for a few weeks to a month as the immune reaction winds down. It is important at the time of diagnosis and treatment to advise patients in this regard or they will often overapply irritating medications or persist in self-treatments that aggravate and prolong the discomfort.

Supplemental Review From General History

In cases of crusted (Norwegian) scabies, a general review should be undertaken seeking a reason for diminished immune response if the reason for this more severe form of the disease is not readily apparent.

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