2025 – PAGE 146 – DERMATOLOGY

LICHEN SCLEROSUS

Lichen sclerosus is a chronic, inflammatory, dry, white, and somewhat scaly rash that is usually found in the genital area. There is no thickening or sclerosis. There are usually no symptoms, although a small percentage of patients have pruritis. Look for a picture of labia with a rash.

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LICHEN STRIATUS

Lichen striatus is a rash that looks like eczema, but is linear or papular and can follow the Lines of Blaschko.

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ALLERGIC CONTACT DERMATITIS, A TYPE IV HYPERSENSITIVITY SKIN RASH

Allergic contact dermatitis is a Type IV hypersensitivity skin rash that requires a prior exposure, and tends to be pruritic. See if the location of the rash is in an area where a nickel-containing belt buckle, earring, necklace, or other jewelry could have been. A rash may present even after years of wearing the irritant. The rash from nickel exposure is more erythematous and can become lichenified. The classic example of Type IV reactions is the rash of poison ivy, poison oak, and poison sumac. A contact dermatitis from these plants will not spread once the affected area is washed with soap and water. The fluid from within the vesicles cannot spread the rash. This reaction is a Type IV Cell Mediated Hypersensitivity Reaction, and is called a Rhus reaction (from the old genus name of poison ivy, Rhus radicans). The rash is vesicular and may be in a linear configuration (where the leaves rubbed across the skin).

• PEARL: First exposure may take 1 week to develop the rash as helper T cells proliferate and “remember” the agent. After that, the rash may develop within hours of exposure. “No wonder I had to go through the 2-step PPD before starting as an attending!”
• PEARL: REMINDERS: A PPD and the skin testing of Candida, Mumps, and Tetanus are all Type IV reactions.
• MNEMONICS:
  • “LEAVES OF THREE, LET THEM BE!” (poison ivy and poison oak have three leaflets)
  • Type IV reaction: I + V = the Roman numeral IV = 4, and the 4^th letter in the alphabet is D = PPD or CD4
  • I + V also should you remind you of poison IV
• IMAGE: www.pbrlinks.com/ALLERGICCONTACT1
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(DOUBLE TAKE) BIOTIN/BIOTINIDASE DEFICIENCY

Biotin and biotinidase deficiencies may present with a RASH + ALOPECIA + NEUROLOGIC SIGNS (ataxia, coma, etc.). Patients may also have lactic acidosis. Treat with biotin.

MNEMONIC: Imagine the rusted TIN MAN from The Wizard of Oz walking with an ATAXIC gait as he SCRATCHES the rusty RASH off his arm. Notice that he has NO HAIR!