Unusual laboratory findings in a case of Norwegian scabies provided a clue to diagnosis

Abstract

The diagnosis of Norwegian scabies was missed for a year for an elderly long-term-care facility resident. Serpiginous tracks were noted on the surface of Sabouraud dextrose agar used for fungal culture of the skin scrapings. This unusual laboratory manifestation must alert clinical microbiologists to the possible diagnosis of scabies.

FIG. 1.

Clinical pictures of patient suffering from Norwegian scabies. Skin lesions on the face (A) and hands (B) of the patient.

FIG. 2.

Laboratory findings in Norwegian scabies. (A) Serpiginous tracks on Sabouraud dextrose agar caused by bacterial overgrowth after overnight incubation. (B) Stereomicroscopic examination of the tracks left by Sarcoptes scabiei on agar surface; the tracks consisted of parallel lanes of imprints, two on each side, representing the four pairs of legs of the adult mite (magnification, ×42.6). (C) S. scabiei mites in potassium hydroxide wet mount of the skin scrapings (magnification, ×28.4).

FIG. 3.

Skin of the patient after 4 weeks of daily application of 25% benzyl benzoate, showing complete resolution of the lesions.