A 17-year-old young man is seen with severe itching of his hands and feet. He has no lesions between his fingers and no one else in the family is itching. He has seen multiple clinicians in the past 5 months and has been given many types of topical steroids and antihistamines. The last clinician referred him for psychotherapy, thinking that this must be psychogenic. On close examination, there are multiple burrows on the hands (Figure 149-1). Dermatoscopy shows the typical pattern of a "jet plane with a contrail," clinching the diagnosis of scabies (Figure 149-2). The patient is treated with permethrin cream overnight and repeated in 7 days. At the following visit his itching is gone, and he is so thankful. This case demonstrates the importance of looking for burrows as the morphologic manifestation of the mite under the skin. Although it was nice to have a dermatoscope to confirm the diagnosis, this diagnosis could easily have been made clinically just by careful observation. Not every patient with scabies has lesions between the fingers and contacts at home with pruritus.
A. Scabies on the hands of a 17-year-old young man. B. Close-up of the right thenar eminence showing two obvious burrows caused by the mites. (Reproduced with permission from Richard P. Usatine, MD.)
Dermatoscopy of a scabies mite showing a jet plane (delta wing) with a contrail-type appearance. The jet plane is the anterior portion of the mite that is darker because of the front legs and mouthparts. The contrail is the burrow that the mite has produced while eating through the epidermis. (Reproduced with permission from Richard P. Usatine, MD.)
Scabies may be one of the most overdiagnosed and underdiagnosed conditions in medicine. Not every patient with a pruritic rash has scabies, and the patterns of scabies are multiple and variable. Scabies may present with papules, pustules, nodules, and/or crusts, and while there are typical patterns of distribution, each case does not read the textbook (not even this textbook). Looking for burrows is always worthwhile, as it is the pathognomonic feature of scabies. Although there may be nodules in the axilla or on the penis, there probably will be some burrows somewhere, such as on the wrist or between the first and second interspace of the hand. Having a dermatoscope to see the real mite is a great advance in the diagnosis of this potentially elusive condition (see Figure 149-2).
Crusted scabies has been called Norwegian scabies. The preferred term is now crusted scabies.