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Is the Simple Saline Mount Technique More Effective than Potassium Hydroxide for the Microscopic Detection of Sarcoptes scabiei?

Scabies is the parasitic infestation of human skin by the mite Sarcoptes scabiei (L.) (Sarcoptiformes: Sarcoptidae). Its clinical manifestations resemble those of numerous other skin diseases; therefore, its definite diagnosis is based on the detection of S. scabiei by a clinical laboratory. Even though various assays have been developed such as epiluminescence microscopy, enzymelinked immunosorbent assay, and real-time quantitative polymerase chain reaction (Wong et al., 2015), the microscopic examination of skin scrapings remains the gold standard for diagnosis as well as the least expensive choice. Skin scrapings are routinely sent to laboratories for a potassium hydroxide (KOH) mount report looking for both fungi and mites. The overall rates of misdiagnosis, however, have been reported to be up to 45% (Anderson and Strowd, 2017). False negative results could be attributed to lack of experience by microbiologists and to the immobilizing effect of KOH to S. scabiei. Kandi (2017) recently suggested that a simple saline mount could be more effective, allowing the observation of moving mites during the microscopic examination (Kandi, 2017). We report a case that supports this suggestion. A 25-yr-old male presented with erythematous scaly papules on his trunk, limbs, and buttocks, as well as nodules along the shaft of the penis, which first appeared 2 mo prior. The patient was initially diagnosed with folliculitis and was treated with antibiotics (doxycycline 100 mg twice a day) and antihistamine. The lesions were not resolved, and topical steroids were subsequently prescribed as treatment for dermatitis. The persistence of the symptoms led him to our clinic. Physical examination revealed 1–3-mm-sized erythematous scaly papules and eczematous erythema on the trunk and limbs, as well as brown nodules ranging in size from 2 to 20 mm on the scrotum and penis. Excoriation and widespread eczema were also noticed as the result of scratching. Itching was reported to be severe and worse at night. The patient was immunocompetent, and no other family members had similar symptoms. Initially, skin scrapings of the patient were examined with a KOH mount where no mites were observed under both 310 and 340 objectives. Because of strong clinical suspicion, however, a subsequent saline mount was prepared and observed thoroughly. Using this methodology, a moving mite was clearly visible at340, confirming the diagnosis of scabies (Fig. 1; Suppl. Video). Negative results for mites in skin scrapings are very common in everyday practice and should not exclude the diagnosis of scabies. Thus, the dermatologist’s approach including the precise communication of a strong clinical suspicion to the laboratory may be decisive. The timely diagnosis of scabies is essential because of the highly contagious nature of the infestation; therefore, the education of health care workers and especially microbiologists about S. scabiei identification techniques is very important. In this regard, and because of the difficulties in the microscopic detection of S. scabiei, our report supports the proposal by Kandi (2017) to perform a simple saline together with a KOH mount when the clinical suspicion of scabies is posed. Overall, to improve the accuracy of lab diagnosis of scabies, more so when scabies is suspected, a simple saline mount should be performed.