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 nakedeye 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
Magnification
