Dermoscopy of Crusted Scabies: Revisiting the New and Old Signs.

Abstract

Dear Editor, Scabies is a common ectoparasitosis in India caused by the eight-legged mite, Sarcoptes scabiei var. hominis. Crusted scabies occurs predominantly in immunosuppressed individuals and presents with diffuse hyperkeratotic scales, crusts, or even erythroderma. It is highly contagious because crusted scabies patient may harbor millions of mites on their body in contrast to 10–12 mites found in classical scabies.[1] It may often be misdiagnosed due to the absence of typical nocturnal pruritus and atypical clinical presentations. Dermoscopy is extremely useful in the diagnosis of this uncommon variant of the common parasitosis. We present a case of crusted scabies showing the classical and newly described dermoscopic signs. A 38-year-old female, case of mixed connective tissue disease, on treatment with daily prednisolone (10 mg) along with azathioprine 100 mg and admitted to the medical ward due to cirrhosis and ascites, presented with skin rash of 1 month duration. On clinical examination, generalized erythematous rash with scaly papules and crusting was seen along with multiple dry crusted hyperkeratotic plaques (showing wet sand appearance) predominantly over the bony prominences, trunk, limbs, and scalp [Figure 1].Figure 1: (a) multiple dry crusted hyperkeratotic plaques with erythematous scaly papules and crusting. (b) scaly crusted plaque involving the scalp. (c) “wet sandpaper” appearance of crusted plaquesDermoscopic examination showed numerous burrows in a “noodle-like pattern” with multiple brownish triangular structures (delta glider sign) [Figure 2a]. These burrows showed the “gray-edged line sign”, which is a gray-brownish line on the outer edges of the burrow (Figure 2b) and wake sign [Figure 3]. Potassium hydroxide (KOH) mount of scales revealed numerous scabies mites and eggs [Figure 4]. On histopathology, hyperkeratosis, parakeratosis, acanthosis, and scabies mites in the stratum corneum were seen [Figure 5]. The patient was advised topical application of 5% permethrin cream every third day for 2 weeks along with oral ivermectin 12 mg to be taken on day 1, 2, and 8.Figure 2: Dermoscopy showing (a) “noodle-like pattern” consisting of accumulation of several curvilinear burrows displaying the “gray-edged line sign” [blue arrowhead (in fig b also)]. (Heine delta NC1, polarized, 10×) (b) brown-colored triangular structure (yellow arrow) that simulates a delta glider trailed by the jet contrail (inset). (Dinolite Videodermoscope polarized non-contact 50x)Figure 3: Wake sign—the burrow (black lines) and the wake-shaped scale (dashed line) together presenting a Y-shaped lesion. (Higher magnification Dinolite Videodermoscope polarized non-contact 50×)Figure 4: Potassium hydroxide mount showing numerous mites (red arrows), eggs (blue arrowhead), and scybala (yellow circles)Figure 5: Multiple scabies mites (black arrow) in stratum corneum (H & E 10x)Burrows are the pathognomonic lesions of scabies; however, they are difficult to be seen on naked eyes, especially in brown skin and in patients with excoriations. Various eponymous dermoscopic signs of scabies include “Delta sign”/“hang glider sign”/“triangle sign” (brownish triangular structures in the shape of hang glider) corresponding to the head and anterior legs of the mite and “Jetliner with contrail sign” (where the mite body appears translucent and air-filled burrow resembles a jetliner with contrail).[2] “Noodle pattern” or “millipede-like structure” (showing numerous burrows) as seen in our case is a characteristic dermoscopy sign of crusted scabies.[3] “Gray-edged line sign” on dermoscopy is a recently described sign where the dark line is often seen on the outer wall of the curved burrow and is supposed to form mainly due to the melanin containing fecal material of the mite, which gets deposited on the outer wall by the tail end of the mite as it crosses the curved burrow.[4] “Wake sign” is described as a pattern of scale reminiscent of the “wake” left on the water surface by a moving object.[5] All the dermoscopic signs were seen in our case. Thus dermoscopy is an extremely useful, rapid, and noninvasive in vivo tool for the diagnosis of crusted scabies. This case is interesting as the dermoscopic signs of noodle pattern and gray-edged line sign have not been previously described in Indian patients. Declaration of patients consent The authors certify that they have obtained all appropriate patient consent forms. In the form, the patient has given his consent for his images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.