Peds- Dermatology

Introduction to Pediatric Dermatology

• Dermatology in pediatrics is often described as the "bread and butter" of the field due to its frequency.

• The diagnostic process is compared to mathematics; by identifying the lesion type and its distribution, the clinician can systematically narrow down the differential diagnosis.

Primary Skin Lesions

Primary lesions are the initial physical manifestations of a disease process, characterized as the first signs to appear on the skin.

• Flat Lesions:

  • Macule: A flat, distinct, discolored area of skin that is less than $1\,cm$ in diameter. An example is a capillary spot.

  • Patch: A flat area of discoloration that is greater than $1\,cm$ in diameter. An example is a Port-wine stain.

• Raised (Solid) Lesions:

  • Papule: A raised, firm lesion that is less than $1\,cm$ in diameter.

  • Plaque: A raised, firm, rough lesion with a flat top surface, greater than $1\,cm$ in diameter.

  • Nodule: A raised, firm lesion, typically greater than $1\,cm$ in diameter, often deeper in the dermis than a papule.

  • Tumor: A larger, soft or firm mass; often broader and deeper than a nodule.

  • Cyst: An encapsulated, closed cavity or sac containing fluid or semi-solid material (e.g., epidermal inclusion cyst).

• Fluid-Filled Lesions:

  • Vesicle: A small, superficial, circumscribed, fluid-filled blister less than $1\,cm$ in diameter. An example is Varicella (Chickenpox).

  • Bulla: A raised, circumscribed, fluid-filled blister greater than $1\,cm$ in diameter.

  • Pustule: A small, circumscribed elevation of the skin that is filled with purulent material (pus).

Secondary Skin Lesions

Secondary lesions result from the evolution of a primary lesion, traumatic injury, or other external factors.

• Scales: Consist of flakes or surface alterations caused by abnormal proliferation of the outermost epidermal layer (stratum corneum). They may be fine, thick, greasy, or loose.

• Crust: Formed by the drying of plasma or exudate on the skin surface; often described as "crusty."

• Lichenification: Skin thickening that occurs over a prolonged period, often due to chronic scratching or rubbing. Commonly seen in chronic eczema.

• Erosion: A slightly depressed area of the skin where part or all of the epidermis has been lost.

• Excoriation: A skin abrasion caused by mechanical trauma, such as scratching a primary lesion.

• Eschar: A dark, black, necrotic tissue covering an ulcer.

• Fissure: A linear cleavage or crack in the skin, often seen on the feet.

• Scar: Permanent fibrotic changes in the skin following the healing of a lesion.

• Keloid: An excessive tissue response to dermal injury characterized by local fibroblast proliferation and overproduction of collagen, causing the scar to thicken significantly beyond the original wound.

Vascular Lesions and Purpura

• Petechiae: Small, pinpoint (less than $2\,mm$) non-blanchable purpuric macules resulting from the rupture of blood vessels. Colors vary (red, purple, or brown). An example is seen in Rocky Mountain Spotted Fever.

• Purpura: Bleeding into the skin resulting in violaceous discoloration ranging from $2\,mm$ to $10\,mm$. Unlike some rashes, purpura does not blanch under pressure. Palpable purpura often represents vasculitis, such as IgA vasculitis (Henoch-Schönlein purpura).

• Ecchymosis: A non-blanching purpuric lesion greater than $1\,cm$ caused by the extravasation of blood into the skin. It changes color over time from blue-black to brown (bruise) and typically results from trauma deeper in the dermis.

Patterns and Distributions of Skin Eruptions

Identifying the arrangement and location of lesions is critical for diagnosis:

• Annular: Ring-like lesions.

• Discrete: Individual, separate lesions.

• Clustered: Multiple lesions grouped together.

• Confluent: Multiple lesions that run together or merge.

• Zosteriform: Lesions following a specific nerve root or dermatome (typical of Herpes Zoster).

• Eczemoid: Lesions resembling eczema.

• Follicular: Lesions specifically involving hair follicles.

• Guttate: "Drop-like" lesions (often seen in certain types of psoriasis).

• Target (Iris) Lesion: Concentric rings resembling a bullseye.

• Morbilliform: Generalized, small, dusky red macules and small patches, commonly seen in viral exanthems like measles.

Viral Infections and Exanthems

• Herpes Simplex Virus (HSV):

  • Type 1 (HSV-1): General face, mouth, lips, or eyes. Acquired via direct contact.

  • Type 2 (HSV-2): Usually acquired via sexual contact or through the birth canal.

  • Neonatal HSV: Treated with Acyclovir regardless of age, especially if exposed via vaginal delivery.

  • Herpetic Whitlow: HSV lesions on the fingers, often from auto-inoculation.

  • Eczema Herpeticum: HSV infection superimposed on eczema; serious if near the eyes as it can spread to the cornea.

  • Diagnosis: Clinical, though DFA testing or the "gold standard" viral culture can be used.

• Herpes Zoster (Shingles): Reactivation of latent Varicella Zoster Virus (VZV) in the sensory nerve root ganglia. A vaccine is recommended for individuals over $60$ to $65$ years old.

• Warts: Caused by Human Papillomavirus (HPV). Treated with Cantharidin (off-label), lasers, or surgery.

• Molluscum Contagiosum: Caused by the Pox virus. Characterized by auto-inoculation (spreading from one site to another on the same person). Treatment involves watchful waiting, Cantharidin, curettage, or cryotherapy.

• Measles (Rubeola):

  • Signs: The "Three C's": Cough, Coryza, and Conjunctivitis (paired with fever).

  • Koplik Spots: Pathognomonic bluish-white spots on the buccal mucosa.

  • Rash: Cephalocaudal distribution (starts on the face and spreads down).

  • Prevention: MMR vaccine given at $1$ year of age (and a second dose at $4$ years).

• Rubella (German Measles): Caused by the Rubella virus. Noted for lymphadenopathy (suboccipital and preauricular). Congenital Rubella Syndrome is a severe concern for pregnant women in the first trimester; the MMR vaccine is live, so pregnancy should be avoided for $6$ months post-vaccination.

• Erythema Infectiosum (Fifth Disease): Caused by Parvovirus $B19$. Common in spring among children aged $4$ to $10$. Features a "slapped cheek" appearance. It can cause an aplastic crisis in patients with Sickle Cell Disease.

• Roseola (Exanthema Subitum): Caused by Human Herpesvirus 6 (HHV-6). Typical history involves a very high fever in an infant, followed by the appearance of a rash only after the fever resides (defervescence).

• Varicella (Chickenpox): Spreads centrifugally (from body outward). Characterized by "dew drops on a rose petal" (vesicles on an erythematous base). A hallmark is seeing lesions in different stages of development in one area.

• Hand, Foot, and Mouth Disease: Caused by Coxsackievirus (A16 is most common). Features an enanthem (oral lesions) and an exanthem (hand and foot lesions). If only oral lesions are present, it is called Herpangina.

Bacterial Skin Infections

• Impetigo: Superficial infection (Staph or Strep). If localized, treat with topical antibiotics; if extensive or toxic, use oral antibiotics.

• Erysipelas: A superficial infection involving dermal lymphatics; well-demarcated swelling and fever.

• Necrotizing Fasciitis: A deep, aggressive infection of the subcutaneous fat and fascia. Often poly-microbial. Characterized by pain out of proportion to the clinical exam. Requires immediate surgical exploration and debridement.

• Ecthyma: A deeper skin infection extending into the dermis, results in "punched-out" ulcers.

• Perianal Bacterial Dermatitis: Usually Group A Strep. Causes intense perianal edema and pain during bowel movements; can be diagnosed with a rapid strep test.

• Acute Paronychia: Inflammation/infection of the periungual fold around the nail.

• Blistering Dactylitis: Infection of the finger pads.

• Folliculitis/Furuncle: Inflammation of the hair follicle; a furuncle is a deeper infection of a single follicle.

Systemic Bacterial Infections

• Lyme Disease: Caused by Borrelia burgdorferi via tick bites. Early localized stage features Erythema Migrans (target/bullseye lesion). Treated with Amoxicillin.

• Meningococcemia: Severe systemic infection (Neisseria meningitidis). Features petechiae and purpura. Treated with third-generation cephalosporins (e.g., Ceftriaxone), then Penicillin once confirmed.

• Rocky Mountain Spotted Fever: Caused by Rickettsia rickettsii via tick bites. Characterized by a rash that specifically involves the palms and soles.

• Scarlet Fever: Result of Group A Strep pyrogenic exotoxin. Features a "sandpaper" rash, circumoral pallor, and a "strawberry tongue."

• Staphylococcal Scalded Skin Syndrome (SSSS): Caused by hematogenous spread of Staph exfoliative toxin, leading to cleavage in the epidermis and blister formation.

• Toxic Shock Syndrome (TSS): Caused by Staph or Strep toxins. A constellation of fever, rash, hypotension, and multi-organ failure.

Fungal and Parasitic Infections

• Candida Diaper Dermatitis: Characterized by bright red skin involving the creases with "satellite lesions."

• Oral Thrush: Common in infants. Treated with Nystatin drops (placed in cheeks to coat the mouth). To distinguish from milk coating, attempt to wipe it off; thrush will not wipe away easily.

• Tinea Corporis (Ringworm): Circular lesions with elevated margins and central clearing. Treated with topical antifungals.

• Tinea Capitis (Scalp): Requires oral treatment (e.g., Griseofulvin) rather than just topical.

• Tinea Versicolor: Scaly patches that may be lighter or darker than surrounding skin; common in summer.

• Cutaneous Larva Migrans: Caused by dog/cat hookworms; features migrating linear lesions. Treated with Albendazole.

Infestations and Insect Bites

• Pediculosis (Lice): Causes pruritus. Treated with topical Malathion or Benzyl alcohol. Children with active lice must stay home, but can return once nits are removed.

• Scabies: Caused by Sarcoptes scabiei. Transmitted by direct contact. Extremely itchy with visible burrows. Treated with $5\%$ Permethrin. The entire family must be treated, and all linens washed in hot water.

Non-Infectious Lesions and Acne

• Atopic Dermatitis (Eczema): Chronic inflammation driven by type 2 inflammation and epidermal barrier defects. Treated with moisturizers and topical steroids.

• Seborrheic Dermatitis: Known as "cradle cap" in infants. Treated with antifungal shampoos or oils.

• Contact Dermatitis: Reaction to irritants or allergens (e.g., metal/nickel). Allergic contact often presents with vesicles and distinct borders, while irritant contact is drier.

• Pityriasis Rosea: Starts with a "Herald Patch," followed by a "Christmas tree pattern" of smaller lesions. Self-limited and non-infectious.

• Acne Vulgaris: Disorder of pilosebaceous follicles.

  • Treatment: Retinoids, Benzoyl Peroxide, and antibiotics (Minocycline/Tetracycline).

  • Isotretinoin: Highly effective but severely teratogenic. Females must use contraception and understand the risks of birth defects.

Pharmacological Considerations

• Topical Steroids: Categorized by potency (mild, medium, high, super-potent). In children, high-potency steroids are avoided to prevent hypothalamic-pituitary axis (HPA) interference through skin absorption.

• Calcineurin Inhibitors: Non-steroid immune modulators (e.g., Tacrolimus). Useful for maintenance therapy because they do not cause HPA axis suppression. However, there is a theoretical risk of malignancy (black box warning) based on animal models, so they are used judiciously.

• Immunotherapy: Used for desensitization in severe atopic dermatitis or allergies via subcutaneous or sublingual routes.

Questions & Discussion

• Question: At what age do you start treating HSV-2 with Acyclovir?

• Response: There is no minimum age; even a newborn exposed during delivery can be treated with Acyclovir to prevent systemic spread, which is dangerous for the infant.

• Question: How do you differentiate between oral thrush and milk coating?

• Response: Milk coating can be easily wiped away with a cloth, whereas thrush is adherent and will not come off easily.

• Question: Do you use a Wood's lamp for Tinea Corporis?

• Response: It is generally not needed; the diagnosis is usually clinical based on the circular lesion with central clearing.

• Question: For Hand, Foot, and Mouth disease, what is the distinction between enanthem and exanthem?

• Response: Enanthem refers specifically to lesions inside the oral cavity. Exanthem refers to the skin rash. If both are present, it is Hand, Foot, and Mouth; if only oral, it is Herpangina.