A patient presents with pruritus and excoriations. He has a poor social situation and appears disheveled. Could this be scabies?
Although some diagnostic algorithms are as simple as finding itching in 2 areas of the body (Mahé Trans R Soc Trop Med Hyg 2005) a closer look may prove rewarding.
Distribution: Infection is spread by direct contact, so regardless of where the infection started, the hands and wrists tend eventually to become infected.(Fathy J Egypt Soc Parasitol 2010) Other prominently affected areas include extensor surfaces, the genitalia, and axillary skin. The head and neck generally are spared.
The lesions eventually just look like excoriations. However, in earlier stages they are papulovesicular or nodular.
A closer look
Burrows are pathognomonic. The term burrow seems to imply that the mites go deep. They do not. These are just epidermal tunnels. The mite makes a serpiginous run through the stratum corneum, chewing up dead skin cells along the way. A silvery burrow can sometimes be seen on close examination with a 0.3mm mite at the very end. They look like a tiny splinter hemorrhage.
Burrow ink test
The original burrow ink test was intended to reveal occult burrows. Rub low viscosity ink on the affected area, wipe off with alcohol, and the tract might be revealed. Tetracycline is used if you intend to cover a large area. The tracts are then visible in ultraviolet light.
Diagnosis can be confirmed with scraping and slide review. The diagnosis is made by finding eggs, mites, or feces. Dermatologists can do this at the bedside using dermoscopy. Generally though this is a clinical diagnosis and such studies are not necessary in the emergency department.
TAKE HOME POINTS
-Scabies prominently affects the hands and avoids the head and neck
-Lesions can be nodular or papulovesicular before being excoriated
-Epidermal burrows are pathognomonic, and sometimes the mite is seen at the end
-The burrow ink test can be used to reveal occult burrows