Scabies Diagnosis: A Narrative Review of Diagnostic Methods, Clinical Misdiagnosis, and Emerging Directions

Caused by the mite Sarcoptes scabiei, scabies is considered a neglected tropical disease that mainly affects the young, elderly and the immunocompromised. The prevalence of scabies is highest in Western Pacific island nations. Despite the high prevalence and recent outbreaks in several high-income countries like the United Kingdom and New Zealand, scabies remains a frequently misdiagnosed disease. Scabies diagnosis often depends on clinical suspicion and the experience of the examining clinician. It is often misdiagnosed as other dermatological conditions like eczema or insect bites due to the low sensitivity of several clinical signs and a lack of a clinically available objective gold standard. This manuscript presents a comprehensive review of tests used to detect scabies, discusses the risks of misdiagnosis and offers suggestions to improve diagnosis. Three databases (PubMed, Scopus, and Web of Science) were searched to identify relevant articles for this review. Diagnostic methods reviewed in this paper include visual inspection, skin scraping, ink test, adhesive tape test, dermoscopy, videodermoscopy, and polymerase chain reaction (nested PCR). Molecular and immunological assays such as PCR and enzyme-linked immunosorbent assay (ELISA) have shown promising specificity and sensitivity of over 80%, which could be considered for diagnosing scabies, especially in cases where clinical signs are unclear. An objective laboratory test for diagnosing scabies is likely to improve control efforts. Use of the 'clinical' and 'suspected' categories of the International Alliance for Control of Scabies (IACS) criteria is also likely to lead to improved diagnosis and treatment of more cases, reducing the risk of misdiagnosis, progression to serious conditions, and limiting disease spread. A consensus on the standardized use of a sensitive objective diagnostic tool is urgently required for resource-poor communities.