A 32 y.o male with a hx of Down's syndrome comes in with a rash

what is it?

Our patient had Norwegian scabies which was identified in the ED by a KOH slide. Norwegian scabies was  first described in Norway by Danielssen and Boaeck  and found in patients with leprosy.  It is a particularly crusted infestation  of mites found in patients with sensory paresthesias , cognitive impairment and immunosuppression.  Patients develop severe erythroderma in 90% of the body surface followed by desquamation.  The differential for diffuse erythroderma includes: eczema, psoriasis, drugs and malignancies.  A simple KOH slide can make the diagnosis.  It is extremely contagious with mites rapidly multiplying into the millions in the skin.

scabies mite seen on KOH

REVIEW OF OTHER SKIN INFESTATIONS

BEDBUGS- Bedbugs have six legs rather than  the eight that mites have. They are ovoid as opposed to rounded and have a banded appearance.  They live in furniture, not on the body and often come out at night to feed.  They can live for up to a year without food. Microscopically blood can often be seen in the digestive tract of bedbugs.

Bedbugs vs scabies. Bedbugs are more spherical after they feed. They have banded bodies.

LICE- Lice have six legs and infest human as either head lice (which do not transmit disease) or body lice(which do transmit disease) .  Lice were responsible for typhus in WWII in the German army on the Eastern front.   Lice are oblong and often tiny white eggs called nits are visible on the base of the hair shaft.

FLEAS- Fleas live predominantly on animals but often cause bites on humans.  They may carry pathogens including plague which is carried in the fleas of infected ground squirrels in the southwest. Fleas have long legs and are known for their jumping skills causing them to be used in “flea circuses”. Fleas have six legs.  Fleas feed on blood.

fleas have long legs which enables them to jump . The bedbug is on the L.

Victorian flea circus

TICKS-  begin life with six legs and then develop another pair.  They are more closely related to spiders and scorpions than insects. Lyme disease, Rocky Mountain spotted fever, tularemia and Erhlichia are the most common tick borne diseases in Missouri. Adult ticks are easily recognized but the nymph and larval ticks are tiny and yet still transmit disease. Ticks are most active from March to mid-May and August to November.

Our patient was treated with Ivermectin 3,000 mcg  in a tapering schedule and permethrin 5% cream. He was incidentally found to be covid + during his hospital stay.

 FUN FACT Sarcoptic mange in dogs is caused by  a mite which cannot complete its life cycle in humans but will cause severe itching until it dies.

 Ebrahim K, Alves J, Felipe de Oliveira  L, et al. Norwegian scabies-rare case of atypical manifestation. An Bras Dermatol 2016 Nov-Dec;91(6):826-828.

Guldbakke K, Khachemoune A. crusted scabies a clinical review. J Drug Dermatol. 2006;5:221-227.