Sarcoptes scabiei seen as superficial cyanoacrylate biopsy specimen. A, In the center of the photograph, the round silhouette of the mite is vaguely apparent (original magnification ×4). B, At magnification ×20, distinctive anatomic features become clearly visible.
Neynaber S, Muehlstaedt M, Flaig MJ, Herzinger T. Use of Superficial Cyanoacrylate Biopsy (SCAB) as an Alternative for Mite Identification in Scabies. Arch Dermatol. 2008;144(1):114-115. doi:10.1001/archdermatol.2007.24
Scabies is an epizoonosis affecting all social groups but with a predilection for people living in day nurseries, nursing homes, or other shared facilities and in resource-poor regions. It is a cutaneous infestation by Sarcoptes scabiei var hominis, a mite ranging in length from 0.2 to 0.5 mm. The mites are transmitted by close and prolonged physical contact.1,2 Sensitization to the mite and its excrements triggers an intensely pruritic skin rash. The patients'
discomfort as well as the transmissibility of the mite makes an early diagnosis desirable. Scabies may mimic a large number of diseases, such as atopic eczema, prurigo, folliculitis, lymphomatoid papulosis, dermatitis herpetiformis, or bullous pemphigoid, thus complicating the process of finding the correct diagnosis. The patient's history, the morphologic characteristics of the skin lesions, and the distribution pattern provide valuable clues. Still, the diagnosis ultimately relies on the detection of the S scabiei mite.
Two basic diagnostic methods are currently in use: (1) Skin scrapings, usually performed with cannulas, needles, or scalpels, are evaluated under a conventional light microscope for direct visual identification of the mite. Alternatively, amplification of S scabiei–specific DNA sequences by polymerase chain reaction can be used as an indirect means of detection. (2) Scabioscopy is used, during which suspect lesions are examined with either a stereoepiluminescence microscope at magnifications ranging from ×20 to ×40 or with a conventional dermoscope, magnification ×10.3 Both scabioscopy and polymerase chain reaction require special equipment and expertise that may not be readily available to every physician faced with the challenge of diagnosing scabies.4,5 Herein, we introduce superficial cyanoacrylate biopsy (SCAB), an inexpensive, easy-to-perform diagnostic technique using readily available resources. The technique was first described by Marks and Dawber6 in 1972 for the examination of the horny layer and later by others.7,8 Glass slides, cyanoacrylate glue (Super Glue; Super Glue Corporation, Rancho Cucamonga, California), and a microscope are at hand in almost every physician's office.
In scabies, a characteristic burrow may be 3 to 8 mm long. Its usually serpentine route is often surrounded by discrete erythema along with pityriasiform scaling. Oftentimes, at one end of a burrow, the mite is visible as a tiny dark dot smaller than 0.4 mm.
We adapted the SCAB procedure for the diagnosis of S scabiei infestation as follows. During a complete inspection of the patient's skin, the most suggestive, nonexcoriated lesions are determined. Hair surrounding these lesions should be removed as needed. The skin is then degreased using an alcoholic disinfectant. A small drop of cyanoacrylate glue is then applied to a glass slide, which is immediately pressed on the skin lesion. After about 30 seconds, the slide is detached from the skin by a swift move. The procedure is repeated in the same way at other suspect sites.
The slides are then examined with a conventional microscope. At scanning magnification, the mites are discernable as tiny dark oval dots. Once candidate objects are identified, thorough identification is possible using a magnification between ×10 and ×200. Typically, the mouth parts and 2 pairs of stumpy legs (sometimes still moving), a corselet with spicules, and singular, fine, long bristles can be distinguished. If these features cannot be identified unambiguously, preincubation with 10% potassium hydroxide for 10 minutes helps to provide a clearer view of the mites by dissolving the corneocytes (Figure).
While in vivo scabioscopy allows for the examination of numerous lesions in little time, thereby potentially increasing sensitivity, the mite is only vaguely distinguishable from crusts by its triangular silhouette corresponding to its mouth and 2 pairs of front legs. In contrast, the SCAB technique, combined with conventional transillumination light microscopy, readily reveals the anatomic features of the scabies mite in detail. In addition, no scalpel or other potentially harmful tool is needed for SCAB, as is needed to perform skin scrapings. A further advantage of SCAB may lie in the possibility to distinguish living from dead mites (eg, after successful therapy) because the procedure removes the mites without harm, making living observation of this unloved cohabitant of human skin possible. Controlled studies are needed to evaluate how SCAB compares with scabioscopy and skin scrapings in terms of sensitivity and specificity.
Correspondence: Dr Neynaber, Klinik und Poliklinik für Dermatologie und Allergologie, Klinikum der Universität München, Frauenlobstr 9-11, 80337 München, Germany (firstname.lastname@example.org).
Financial Disclosure: None reported.