A burrow on the side of the finger near the web space.
A burrow on the side of the finger near the web space.
Scabies is the infestation of the skin by the scabies mite. Intense itching caused an allergic contact dermatitis to the mite, its eggs and feces ensues.
The patient presents with intense itching. It is often worse at night, but this may be because there is nothing to distract the patient from the itch. Other members of the family are often affected. The best place to see the burrows, which appear as 3-10 mm thread-like lines, is between the fingers in the web spaces and along the sides of the feet. Red papules on the penis are classic and are highly suggestive. Diffuse itching and red 2-4 mm bumps on the penis are almost always scabies.
Crusted scabies is a severe and highly contagious form of scabies in which thousands of mites trigger diffuse crusting and even thick, hyperkeratotic plaques.
For the experienced clinician, seeing even one classic burrow establishes the diagnosis. In uncertain cases or in order to confirm the diagnosis, dermoscopy is used by many dermatologists. In typical cases, burrows may be readily identified. At 20-40 magnification, the mite's head and 2 pairs of forelegs resemble the triangular shape of a hang-glider. Sometimes the contour of the round body of the mite can also be identified. The adhesive tape test is convenient and a valuable screening tool. For that, strips of tape are applied to areas suspected of being burrows and then rapidly pulled off. These are then applied to microscope slides and examined. Finally, a KOH or mineral oil examination may be done. Suspected burrows and itchy papules are scraped with a mineral oil-coated blade. The material is applied to a slide, oil added and examined microscopically.
Permethrin cream is first-line and more effective than oral ivermectin.
Give an amount sufficient for all people in the household with the following instructions: Apply from the neck down and leave on overnight. Apply to the scalp in children under 3 and anyone with an itchy scalp. Every nook and cranny of the skin must be covered. If one patient misses one spot, it could all come back. Wash all clothing in warm or hot water and then dry in the dryer. Cloth items which cannot be laundered may be stored for ten days. In the AM, wash all sheets and take a shower. A medium-potency topical steroid (e.g., triamcinolone 0.1%) may be given for 2 weeks as the itching takes a while to subside. Alternatively, some give IM triamcinolone, e.g., 40 mg. A scabies handout is available.
Ivermectin is usually given 200 ug/kg as a single dose and repeated in 7-14 days. This is CDC-recommended but not FDA-approved. Ivermectin alone is frequently ineffective in this author's experience and should be combined with topical permethrin. It shouldn't be used in pregnancy, in those breastfeeding, or in those less than 15 kg (where the blood-brain barrier is less effective and the risk of seizures is higher). Topical ivermectin 1% (Soolantra) is effective but off-label and very expensive.
If the patient calls, saying the scabies is back, consider the following:
Permethrin, topical sulfur, benzyl benzoate, and crotamiton are all considered safe during pregnancy.
Elimite is not FDA-approved for infants less than 2 months of age. Precipitated sulfur 6 or 10% compounded in petrolatum is the treatment of choice here. It is applied all over including the face and scalp but avoiding the eyes and mouth for 3 consecutive nights. It is also safe in pregnancy.
Many clinicians feel comfortable giving permethrin to infants < 2 months.
In an interesting study in the Fijian Islands, mass administration of oral ivermectin reduced the prevalence of scabies over the next 12 months from 32.1% to 1.9% [N Engl J Med 2015; 373:2305-2313].
Burrows on the wrist
Crusted Scabies
Scabies of the penis. Red macules and papules are seen. A burrow may be visible atop a papule.
Who is Dr. White? | Privacy Policy | FAQs | Use of Images | Contact Dr. White