Diagnosis: Scabies
Scabies is a diagnosis that should be considered in any patient with new-onset, widespread, nocturnal-dominant pruritus1 and it was suspected, in this case, after the initial history taking and physical exam. (See “Consider these diagnoses in cases of pruritic skin conditions” for more on lichen planus and prurigo nodularis, which were also included in the differential diagnosis.)
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Consider these diagnoses in cases of pruritic skin conditions
Lichen planus is a chronic inflammatory condition that mostly affects the skin and mucosa. Characteristic findings are groups of shiny, flat-topped, firm papules. This patient’s widespread nodular lesions with rough scales were not typical of lichen planus, which usually manifests with flat (hence the name “planus”) and shiny lesions.
Prurigo nodularis is a chronic condition that manifests as intensely itchy, firm papules. The lesions can appear anywhere on the body, but more commonly are found on the extremities, back, and torso. The recent manifestation of the patient’s lesions and her lack of a history of chronic dermatitis argued against this diagnosis.
The use of a handheld dermatoscope confirmed the diagnosis by revealing white to yellow scales following the serpiginous lines. These serpiginous lines resembled scabies burrows, and at the end of some burrows, small triangular and hyperpigmented structures resembling “delta-winged jets” were seen. These “delta-winged jets” were the mite’s pigmented mouth parts and anterior legs. The burrows, which contain eggs and feces, have been described as the “contrails” behind the jets (FIGURE 2).
The use of a new UV illumination feature on our dermatoscope (which we’ll describe shortly) made for an even more dramatic diagnostic visual. With the click of a button, the mites fluoresced green to yellow and the burrows fluoresced white to blue (FIGURE 3).
Meeting the criteria. The clinical and dermoscopic findings met the 2020 International Alliance for the Control of Scabies (IACS) Consensus Criteria for the Diagnosis of Scabies,2 confirming the diagnosis in this patient. Scabies infestation poses a significant public health burden globally, with an estimated incidence of more than 454 million in 2016.3
Visualization is key to the diagnosis
Traditionally, the diagnosis of scabies infestation is made by direct visualization of mites via microscopy of skin scrapings.4 However, this approach is seldom feasible in a family medicine office. Fortunately, the 2020 IACS criteria included dermoscopy as a Level A diagnostic method for confirmed scabies.
Continue to: The pros and cons of dermoscopy