Dermatología: Dermatitis y Urticaria

Fisiopatología Unidad 3

• Síndromes Reaccionales: These syndromes have an immunological basis and are associated with hypersensitivity responses triggered by substances.

• Hypersensitivity responses can be categorized as: humoral or cellular.

• There is a possibility of developing immunological memory.

• These syndromes manifest in various patterns on the skin.

• Dermatitis de Contacto: Is an inflammatory skin condition caused by direct application of chemicals.

• Symptoms vary from acute/eczematous to chronic/lichenified.

• Common causes in Mexico include detergents (especially in women), nickel (jewelry), medications, chromium (cement), latex, or certain materials used in manufacturing goods.

Aspectos Generales

• Definition of Reactional Syndrome: An inflammatory skin response due to chemical application, directly or via an immunological process, without entering the bloodstream.
• Epidemiology: This is the most frequent type of skin syndrome, accounting for 10% of all skin conditions and between 5-10% of consultations in dermatology. It accounts for 25 to 50% of work-related skin issues in hands.
• Further Key Causes in Mexico: Detergents (more common in women), nickel (often in women), medications, and chromium (more common in men). Other causes include latex, paper products (colophony, formaldehyde), and rubber products(more elastic than rubber) in certain industries.

Fisiopatología

• Mechanism: Primarily mediated by Type IV Hypersensitivity mechanisms.
• Duration: Can last from days to a lifetime.
• Stimuli: Can be triggered by primary irritants (no prior immunity) or by sensitizing agents (associated with an immune response).

Causas Más Frecuentes (Specific Causes)

• Primary Irritants: Acids, alkalis, inorganic salts (e.g., hydrochloric, hydrofluoric, nitric, chromic acid, sodium hydroxide).
• Examples: Urine, feces, oxalic acid (found in some plants and creatures), tanning materials, plastics, solvents, and oxidizers. Certain resins, reducing agents, and dyes are also mentioned as possible causes.
• Medications: Antiseptics (permanganate of potassium, gentian violet, mercury compounds), and other products detailed in the data.

Causas más frecuentes (by category)

• Irritantes primarios: Acids, álcalis, sales inorgánicas.
• Sustancias químicas: Ammonia, ácidos orgánicos, productos industriales, medicamentos.
• Other categories of causes: (i.e. cosmetics, metals, clothes, and more)

Fototóxicas

• Medicamentos: Tetracycline, nalidixic acid, sulfonamides, sulfonylureas, chlordiazepoxide, griseofulvina, thiazides, phenothiazines.
• Otras: Citrus fruit essence, psoralens, anthraquinones, acridine derivatives, eosin, fluorescein, methylene blue.

Fotoalérgicas

• Medicamentos: Antihistamines, hypnotics, psychoactive drugs, phenothiazines, urinary antiseptics, sulfonamides.
• Other: Hexachlorophene, PABA derivatives, cinnamic acid esters.

Dermatitis por Contacto (Irritante Primario y Fototoxicidad)

• Common agents: Soaps, detergents, acids, alkalis, organic solvents, oxidants, formaldehyde, and certain dyes (like gentian violet).
• No immune involvement: A reaction happens from the first time of contact and the severity varies by concentration and duration of contact.
• Other characteristics: No immune factors involved, the response is not dependent on previous exposure.

Dermatitis por Contacto (Sensibilización y Fotoalergia)

• Involves immune response: This type of dermatitis involves an immune system reaction, the reaction is not immediate and can occur several days after contact with the substance.
• More diverse range of agents: Medications, cosmetics, metals (e.g., nickel, chromium, cobalt), clothing materials (fabrics, shoes), plastics, and home remedies.
• Features: Reaction not immediate, involvement of T lymphocytes, passive transfer possible

Relación Ubicación/Agente Causal

• Specific substances are related to certain areas of the body.

Manifestaciones Clínicas

• General characteristics: Variable location. A direct relationship exists between site of contact with the causal agent and the location of the reaction. Commonly appears on exposed areas, especially hands. Characterized by variations depending on the time course.
• Acute vs Chronic manifestations: Acute: erythema, vesicles, melicery crusts, hemorrhagic crust, no precise borders. Chronic: lichenification and hemorrhagic crust in more clearly defined areas.

Dermatitis de Pañal

• Definition: An acute inflammatory condition affecting the diaper area in infants.
• Epidemiology: Affects primarily infants aged 9-12 months or individuals with incontinence. High incidence rates within pediatric clinics. A frequent diagnosis in Mexico.

Fisiopatología (Diarrea)

• Factors: Age, diet, diaper changes, hygiene practices, racial and environmental factors.
• Causes: Prolonged contact with urine, feces, occlusive dressings, disposable diapers, rubber pants, high temperatures, humidity, and friction. These factors harm the skin barrier's function which allows for penetration of irritants like ammonia, etc.

Fisiopatología (Diarrea)

• Factors: Bacteria in feces break down urine urea releasing ammonia, increasing pH. Increased pH enhances activity of lipases and proteases in feces provoking skin irritation and epidermal barrier damage.
• Mechanisms: Increased acidity in the area, high temperatures, moisture make the area vulnerable.
• Factors: Ammonia, increased pH, increased temperature and moisture contribute to a microenvironment favorable for bacteria like Candida.

Manifestaciones Clínicas (for Diaper Rash)

• Early stages: Erythema, well-defined region.
• Progression: Eruption can progress. Possible intense pruritus, oozing, and erosion.
• Chronic cases: Possible lichenification.

Eritrodermias

• Definition: A severe, acute or chronic inflammatory condition of the epidermis that affects a large portion of the skin's surface. 
• Causes: Reactions to medications (16% to 48%), lymphomas (12% - 17% in people under 70), and idiopathic factors. Predominant in men and usually after 40-50 years of age. 

Manifestaciones Clínicas (Eritrodermias)

• Site: Can appear on skin, mucous membranes, and appendages; can be systemic.
• Skin changes: Erythema, extensive scaling (affecting >90% body surface), possible discoloration (violaceous or purplish), white or yellow scaling, intense itching. 
• Other: Palmoplantar keratoderma (thickening and scaling on palms and soles), difficulty moving facial muscles or fingers, hair loss, nail changes.
• Possible: 65% of patients with multiple lymph node enlargement.

Prurigo por Insectos

• General: Skin reaction due to insect bites, often affecting children; it often manifests with symmetrical distribution.
• Causes: Primarily bed bugs, fleas, and other external parasites like mites, mosquitoes.
• Lesions: Itching welts (wheals), papules, crusting, skin sores, and sometimes blisters. Localized to areas of body exposed to the bugs.

Urticaria

• Characteristics: Characterized by wheals, or hives, which are raised, itchy, red welts on the skin. 
• Causes: Variety of causes, some identifiable (drug reactions, infections, food allergies), but many cases have no clear or identifiable source. 
• Types: Acute (< 6 weeks) and chronic (> 6 weeks).