2025 – PAGE 145 – DERMATOLOGY

SEBORRHEIC DERMATITIS (AKA CRADLE CAP)

Seborrheic dermatitis (AKA cradle cap), is a NONpruritic, inflammatory, flaky rash with white to yellow scales that usually forms in oily areas (e.g., scalp). It is often seen in the first two months of life. After that, it’s not very common until adolescence. You may treat with topical antifungal agents or mild steroids. The skin may be left with hypopigmented areas, especially in the folds. If asked to name the hypopigmented areas, choose PITYRIASIS ALBA.

IMAGE: www.pbrlinks.com/SEBORRHEIC1

PSORIASIS

Psoriasis is a very well-defined, red, flaky rash covered with silver-white patches, called plaques. It can also be described as thick and scaly (like seborrheic dermatitis). It sometimes results in punctate bleeding when scales are removed (this is called the Auspitz sign). It can occasionally be limited to the diaper area, in which case it goes into the inguinal folds. Topical steroids are the mainstay of treatment. For the face, use topical calcineurin inhibitors (tacrolimus or pimecrolimus). For severe disease, or disease not responding to steroids, use phototherapy, methotrexate or etanercept.

GUTTATE PSORIASIS

The “guttate” in guttate psoriasis means “drop like” and describes the shape of these discrete psoriatic lesions. This can be preceded by a Group A Strep (pyogenes) infection.

IMAGE: www.pbrlinks.com/GUTTATE1

(DOUBLE TAKE) LANGERHANS CELL HISTIOCYTOSIS (LCH) = HISTIOCYTOSIS X

Langerhans Cell Histiocytosis (LCH), AKA Histiocytosis X, is a PAPULAR rash that is sometimes associated with petechiae. The rash is located in the folds (inguinal folds, supra-pubic folds, perianal area). It can resemble eczema, but the petechiae or PAPULES should guide you towards this diagnosis. LCH is a type of cancer. You may be shown a lytic bone lesion (possibly of the skull). Diagnose by skin biopsy. LCH can also be associated with DIABETES INSIPIDUS. Treat by removing the lesion and giving steroids, ± chemotherapy.

PEARLS:  Do not confuse this with Wiskott-Aldrich (WiXotT-Aldrich, X-linked, low IgM, high IgA, TIE = Thrombocytopenia, small platelets, Infections, and Eczema). Also, if they describe an eczema or seborrheic dermatitis type of rash in a patient with high urine output, LCH is your diagnosis.

IMAGE: www.pbrlinks.com/LANGERHANSCELL1
IMAGE: www.pbrlinks.com/LANGERHANSCELL2
IMAGE: www.pbrlinks.com/LANGERHANSCELL3

RASHES THAT SPARE THE INGUINAL FOLDS

Eczema and Contact Dermatitis should be high on your differential for rashes that spare the inguinal folds.

PRURITIC RASHES

Consider atopic dermatitis/eczema, HSV, scabies, tinea, or Varicella (VZV) in your differential of any pruritic rashes.

KERATOSIS PILARIS

Keratosis pilaris forms due to an overgrowth of the horny skin. It can look similar to eczema and may have a mild erythematous background. No treatment is needed.

IMAGE: www.pbrlinks.com/KERATOSIS1
IMAGE: www.pbrlinks.com/KERATOSIS2
IMAGE: www.pbrlinks.com/KERATOSIS3