Figure 2. Higher magnification shows three pink pigtail-like structures, one attached to the stratum corneum and other two free in the burrow cavity.
Sarcoptes scabiei is an obligate ectoparasite, which burrows into the stratum granulosum of the epidermis and lays its eggs. The resultant host inflammatory response leads to intensely pruritic papules. CASE SYNOPSIS: A 63-year-old man undergoing treatment for immunoproliferative disease was suspected of having a pruritic drug eruption. Subsequent skin biopsy revealed an intracorneal burrow containing three pink, refractile pigtail-like structures, believed to be empty eggshells of S. scabiei. CONCLUSION: Traditionally, the presence of adult mites or eggs in skin scrapings or a skin biopsy is required for a definitive diagnosis of scabies. However, our case and similar cases suggest that the diagnosis of scabies can also be made on the basis of pink pigtail-like structures, remnants of eggshells, within the intracorneal burrow.
|
|
| Figure 1 | Figure 2 |
|---|---|
| Figure 1. Intracorneal burrow containing pink pigtail-like structures (arrow). Figure 2. Higher magnification shows three pink pigtail-like structures, one attached to the stratum corneum and other two free in the burrow cavity. |
|
A 63-year-old man undergoing treatment for immunoproliferative disease was suspected of having a pruritic drug eruption. Subsequent skin biopsy revealed an intracorneal burrow containing three pink, refractile pigtail-like structures, one attached to the stratum corneum and the other two free in the burrow cavity (Figures 1 and 2).
Sarcoptes scabiei is an eight-legged, tan-brown obligate ectoparasitic arachnid that is transmitted by direct and prolonged person-to-person contact. As a result of this means of transmission, scabies is largely believed to be a disease of overcrowding and close-proximity and not an indication of poor hygiene [1]. Typically measuring 0.3 to 0.5 mm, the female mite burrows into the stratum granulosum of the epidermis. From there, it continues to move and lay eggs along the way, eventually dying within two to three months.
Clinically, affected individuals present with symptoms two to four weeks following the initial infestation; they primarily complain of intense itching that worsens at night. Examination of the skin demonstrates the presence of small, erythematous papules, which may show thin burrow lines measuring several millimeters in length. The pruritic papules in patients with scabies are classically located in the webs of the fingers, the flexor aspects of the wrists, the extensor surfaces of the elbows, the periumbilical skin, buttocks, ankles, and genital areas. The back and head are spared in most cases. On the more severe end of the clinical spectrum, crusted scabies is a debilitating disease characterized by very large numbers of mites that cause the development of hyperkeratotic crusts that may affect the neck, scalp, face, eyelids, and subungual sites. Whereas crusted scabies is often associated with chronic infections, debilitation, and immunosuppression, cases in apparently immunocompetent hosts have been described [2]. As a result of frequent scratching that produces open excoriations, secondary infections, especially group A streptococci and Staphylococcus aureus can result in cellulitis and more invasive bacterial infections. Scabies infestations are primarily treated with topical agents, such as permethrin cream (5%), or oral antihelmintics, such as ivermectin (200 mcg per kg in one dose, which may be repeated in 2 weeks). In individuals with more severe disease, extended treatment may be necessary.
Whereas a skin scraping is the more traditional means of detection, occasionally when the diagnosis of scabies is missed clinically, evidence of a scabies infection can also be observed on skin biopsy. In these cases, histopathological findings may include burrows in the stratum corneum, parakeratotic mounds, inflammatory cell infiltrates (lymphocytes, histiocytes, and eosinophils), adult mites, and embryonated eggs in various stages of development [3]. Traditionally, a definitive diagnosis of an infection by S. scabiei has been reserved for cases in which skin scraping or biopsy demonstrates an adult mite or an egg. Whereas these findings are very specific for scabies, sensitivity is less than 50 percent because only a few mites or eggs may be present in the skin at any time during infection. Poor sensitivity may lead to an uncertain diagnosis, a delay in treatment, and possibly an increased risk of secondary infection. More recent advances in the development of an S. scabiei immunodiagnostic assay are underway and may yield a more sensitive means of diagnosing individuals, thus leading to selective treatment of individuals in endemic areas [1].
In our case, no mites or eggs were visible in the biopsy specimen. However, there were distinctly visible pink pigtail-like structures within the intracorneal burrow. In serial sections the mite may be seen at various stages of development demonstrating that these pigtail structures are formed as the scabies egg hatches and leaves behind an empty shell [4]. In agreement with the observation of other authors [4], our case suggests that it is possible to make a diagnosis of scabies without a visible egg or mite when these pink pigtail structures, indicative of empty scabies eggshells, are observed. In such cases, a prompt diagnosis will allow timely treatment of the infection.
© 2011 Dermatology Online Journal