2025 – PAGE 160 – DERMATOLOGY

SCABIES

Scabies presents as linear, papular, erythematous, pruritic, vesicular, and crusting lesions most often seen in areas with CREASES (wrist, groin, webbing of fingers). You may see burrows. Treat the entire family with permethrin overnight (8-14 hours) from neck to toe and wash off the next morning for the entire family. Re-treat the patient 7-10 days later because eggs can hatch up to 10 days later. Try topical steroids or antihistamines for symptomatic cares in the interim. An alternative treatment is oral ivermectin due to ease of administration in older children.

PEARL: Unlike papular urticaria, lesions are not in crops.

IMAGE: www.pbrlinks.com/SCABIES1

PEDICULOSIS CAPITIS (AKA HEAD LICE)

Pediculosis capitis (AKA head lice) results in nits/ova of the lice at the hair shafts, especially in the occipital area. Treat with permethrin. The patient may have more symptoms at night when lice tend to be more active. Itching is from the bites. Similar to scabies, repeat permethrin again in 7–10 days because eggs can hatch up to 10 days later. Oral ivermectin is also a possible treatment, especially if the lice are found to be resistant to the topical treatments.

PEARL: African American children are much less likely to get head lice per the CDC. So think twice about selecting head lice in the answer for board questions that include an African American child.

IMAGE: www.pbrlinks.com/HEADLICE1

PEDICULOSIS PUBIS (AKA PUBIC LICE or CRABS)

Pediculosis pubis (AKA pubic lice or crabs) is an infection in the groin that results in red, crusted suprapubic macules and possibly bluish-gray dots. There is a STRONG ASSOCIATION with sexual abuse in children.

IMAGE: www.pbrlinks.com/CRABS1

THE “ERYTHEMA” RASHES

ERYTHEMA NODOSUM

For erythema nodosum, look for PAINFUL, shiny, red to bluish skin lesions in a patient with a history of a chronic disease or on certain medications. Associations include Crohn’s Disease, Ulcerative Colitis, Drugs (oral contraceptives and sulfa drugs), Infections (Yersinia, EBV, Tuberculosis, fungal infections), and Sarcoidosis.

MNEMONIC: For this shiny skin finding, use CUDIS (kind of like CUTIS, which means skin) to help you remember the following associations: Crohn’s, UC, Drugs, Infections, and Sarcoidosis.

IMAGE: www.pbrlinks.com/ERYTHEMA-N1
IMAGE: www.pbrlinks.com/ERYTHEMA-N2
IMAGE: www.pbrlinks.com/ERYTHEMA-N3

(DOUBLE TAKE) ERYTHEMA CHRONICUM MIGRANS

Erythema chronicum migrans (AKA erythema migrans) is caused by BORRELIA BURGDORFERI, the spirochete that causes LYME DISEASE. Look for a large, flat lesion (> 5 cm) that is annular and has a red border. It is located at the tick bite site in about 75% of patients. The classic description is a “bulls eye” lesion. The rash shows up 1–2 weeks after the bite. Titers may still be negative during this period. Borrelia is transmitted via the Ixodes deer tick. Oral doxycycline is usually the first-line treatment for Lyme disease, including for arthritis, disseminated erythema migrans, a palsy (BELL’S PALSY), or neuropathy. For children under 8 years old, doxycycline is safe to use for up to 21 days. Use amoxicillin for children < 8 years old who need treatment for longer than 21 days. IV ceftriaxone is preferred for unstable or hospitalized patients, such as patients with encephalitis or symptomatic CARDITIS, or for RECURRENT arthritis if the patient has failed doxycycline therapy. Arthritis is usually located at the large joints (especially the knees). Diagnosing using labs is often difficult. Obtain Lyme antibody titers. If these are positive, confirm with a Western blot. Lyme Disease is often a clinical diagnosis (for example, if you see erythema migrans, TREAT).

• IMAGE: (BULLSEYE LESION) www.pbrlinks.com/ERYTHEMA-C1
• IMAGE: (BELL’S PALSY) www.pbrlinks.com/ERYTHEMA-C2
• SIDE NOTES
  • BELL’S PALSY: Unilateralfacial nerve paralysis (CN VII). It is often idiopathic.
  • The Jarisch-Herxheimer reactionresults in fever, chills, hypotension, headache, myalgia, and exacerbation of skin lesions during antibiotic treatment of a bacterial disease (typically spirochetes). This is due to large quantities of toxins released into the body. It is classically associated with syphilis but can also occur with Lyme disease. It may only last a few hours.
• MNEMONICS:
  • From now on, think/say borreLIYME. “Don’t ever throw a borreLIYME to MY GRANny!” Or, “Don’t ever borre-LIE to MY GRANny.” borreLIYME = Borrelia. MY GRANny = Migrans.
  • Imagine that BULL’S EYES are made of two bright neon-green LIMES! This should remind of you of the classic description.
  • Imagine squeezing LYME into a CAN = Carditis, Arthritis, and Neuritis.