Severe itching should prompt suspicion for scabies and the hands are the highest-yield location. In this patient’s case, there weren’t findings in the web spaces and, in general, skin findings were largely absent; dermoscopy confirmed the diagnosis of scabies.
Sarcoptes scabiei, is a parasitic mite that lives and reproduces in and on human skin and is transmitted by very close contact, either skin-to-skin or by living within a household or institution with shared linens and furnishings. After infection, itching develops within days to weeks from both the physical movement and burrowing of mites within the skin and from the allergic and inflammatory response to mite bodies and their waste.1 Symptoms and infections may persist for years in the absence of treatment.
Sometimes (as in this case), burrows are few and very subtle. More often, there are widespread burrows and excoriated papules over the hands, trunk, extremities, and genitals. A burrowed mite is often adjacent to, but not directly in, an excoriation. Dermoscopy has transformed the ability to diagnose this condition quickly by enabling clinicians to visualize the triangular shape of the head and front legs of a mite (called the “delta sign”). This localization allows easy microscopic confirmation by paring the mite from the skin with a small scalpel blade. (A #11 or #15 blade works very well.)
Topical permethrin 5% cream is highly curative. The cream should be applied from the top of the neck to the tips of the patient’s toes and left on for 8 hours; the process should be repeated a week later. Very close contacts (eg, symptomatic household members or sexual partners) should be treated concurrently. A 60 g tube will treat 1 adult twice. (A 60 g tube of permethrin with a refill, therefore, will treat 2 adults twice.) Oral ivermectin 3 mg dosed at 200 mcg/kg in a single dose repeated in 1 to 2 weeks is an alternative.
Outbreaks in an institutional setting present a significant challenge and require population-based control and often the assistance of infection control specialists or local public health officials. Often this involves weekly treatment with ivermectin for all potentially affected individuals for 3 to 4 weeks and surveillance for follow-up. While there is some resistance to ivermectin, many failures relate more to reinfection from unidentified sources.
This patient received topical permethrin 5% cream dosed as noted above. Itching can be expected to persist for 3 to 4 weeks, so topical triamcinolone 0.1% cream was prescribed as needed for itching on days when permethrin wasn’t applied. At 6 weeks, this patient’s symptoms had resolved.
Photos and text for Photo Rounds Friday courtesy of Jonathan Karnes, MD (copyright retained). Dr. Karnes is the medical director of MDFMR Dermatology Services, Augusta, ME.