Itching and rash in a boy and his grandmother

Journal of Family Practice, August, 2006 by Gary N. Fox, Richard P. Usatine

A boy came to the office with a rash and progressively severe itching for approximately 2 months (FIGURE 1). Examination showed an excoriated generalized papular eruption, including some urticarial-type papules and chronic eczematoid changes near the waist, axillae, hands, and wrists.

[FIGURE 1 OMITTED]

His grandmother, with whom he spends most weekends and a lot of time after school, also has had a rash and progressive itch for approximately 3 weeks. One feature of the dermopathy observed clinically, first located by hand lens examination and then confirmed by dermoscopy, is depicted in FIGURE 2.

[FIGURE 2 OMITTED]

* What is your diagnosis?

* Diagnosis: Scabies

The boy and his grandmother both have scabies, an infectious disease--in fact, the first human disease proven to be caused by a specific agent. (1) Sarcoptes scabiei var hominis, or scabies, is a mite in the arachnid class. (2) In some states and localities, scabies cases or scabies outbreaks are reportable to the public health department.

The cardinal symptom of scabies is pruritus. The itch, especially with initial scabietic infestation, may be gradual in onset. (3) Physical examination findings can vary from subtle and nonspecific to overwhelming and distinctive. Scabies can also mimic other dermopathies, complicating diagnosis. Undiagnosed and untreated, scabies can last a protracted period.

The dermopathy may be characterized by urticarial-type papules, vesicles, eczematoid change, excoriation, and bacterial superinfection, especially in children. Nodules may be present, particularly on the penis and scrotum. These may last for months after the infestation has cleared. (3) The most commonly involved areas include fingers and finger webs, wrist folds, elbows, knees, the lower abdomen, armpits, thighs, male genitals, nipples, breasts, buttocks, and shoulder blades. (3,4) In young children, scabies may be found anywhere, including palms, soles, face and scalp.

Affliction of multiple family members and finding dermatitis in these distinctive locations is helpful in diagnosis. Finding the mites' burrows is considered pathognomonic because other burrowing diseases (eg, cutaneous larva migrans) are easily distinguished clinically. (4) Extensive excoriation is a clinical clue to look for burrows. (3)

Transmission usually skin-to-skin

Scabies is generally transmitted by prolonged skin-to-skin contact, such as occurs in families or during sexual contact. It is possible to acquire scabies infestation via contaminated items of clothing or bed linens, but this is not regarded as a significant route of transmission. (3) Transmission by casual contact, such as a handshake or hug, is unlikely.

Infestation with the S scabiei mite, referred to as scabies in man, is termed "mange" in other mammals known to host the mite (dogs, cats, rabbits, cattle, pigs, and horses). Mites from one host species generally do not establish themselves on another species, and thus are referred to as varieties, variants, or forms. Humans develop a transient dermopathy from infestation by animal scabies, but such infestations are mild and disappear spontaneously unless the person is in frequent contact with the infested animal. (3,4)

Differential diagnosis

The differential diagnosis of scabies--a great masquerader--is extensive, and includes atopic dermatitis, contact dermatitis, impetigo, insect bites, vasculitis, neurodermatitis, folliculitis, prurigo nodularis, psoriasis (crusted scabies), and a host of other dermopathies. (3,4)

* Confirming the diagnosis

Finding the causative mite, its ova (eggs), or scybala (feces), confirms the diagnosis, although failure to find these does not rule out scabies. Papules or burrows that have not been excoriated are best for obtaining preparations for microscopic examination. (3) Burrows may be found with naked-eye inspection, although use of a hand-held magnifier and good illumination make finding burrows easier.

Dermoscopy

Dermoscopy, performed with an otoscope-like, illuminated magnifier designed for skin assessment, provides reliable confirmation of S- or Z-shaped burrows. During dermoscopy, carefully examining the distal end of the burrows in the skin may reveal the "triangular black dot" of the scabies mite (FIGURE 2, top right)--the head of the mite. (5) The body of the mite--light in color and oval--is not visible even with the most careful dermoscopic examination. The "black dot" of the mite may be visible with careful inspection with a hand lens. In the appropriate clinical setting, dermoscopic identification of an unequivocal burrow with the dark "triangle sign" at one end is diagnostic for scabies. When a digital photograph obtained through the dermatoscope is magnified, the distal end of the burrow (FIGURE 3) reveals the triangular head parts of the mite and the body within the burrow. This body is not evident with dermoscopy alone; the additional magnification via photography allows its visualization.

[FIGURE 3 OMITTED]

Scabies mount

In instances where the physician is going to make an institution-wide recommendation with major ramifications, it is wise to positively identify the mite. A scabies mount performed at the location of the triangular dot will readily provide a mite for identification. Scabies mounts are prepared via a very superficial shave technique without anesthesia. The skin flakes are transferred to a slide and a drop of mineral oil is added. Alternatively, a drop of mineral oil can be placed on the skin and a superficial sample obtained.