Common Dermatoses

Definition: Psoriasis is the most common chronic papulosquamous disease.
Classic Lesion Characteristics:
- Well-demarcated erythematous plaque with a silvery (micaceous) scale.
- Removal of the scale can result in bleeding, known as Auspitz sign.
Prevalence: Affects approximately 2% of the population.
Nature of Disease:
- Chronic inflammatory disease associated with systemic impacts that may be preventable.
- Associated conditions include cardiovascular disease, obesity, and smoking, which precede moderate to severe psoriasis development.
Management: Early, aggressive treatment can lessen co-morbidities and improve survival.

Psoriasis vulgaris: The most common form.
Guttate psoriasis: Often follows streptococcal infection.
Pustular psoriasis: Characterized by pustules.
Inverse psoriasis: Occurs in skin folds.
Erythrodermic psoriasis: A severe form that can cover large areas of the body.

Epidemiology: Affects between 7% and 21% of patients with psoriasis.
Onset: Can occur:
- Before psoriasis,
- Concurrent with psoriasis,
- After psoriasis.
Risk Factors: More common in those with moderate to severe cutaneous disease and those with nail involvement.

Definition: A non-infectious, immunologically mediated skin disorder.
Pathophysiology: Characterized by lymphocytes attacking the epidermis.
Associated Conditions: Frequently associated with autoimmune disorders, including:
- Alopecia areata,
- Ulcerative colitis.
Aetiology: Unknown but may include:
- Drugs (e.g., streptomycin, chloroquine, methyldopa, phenothiazine),
- Bone marrow transplants,
- Hepatitis C infection,
- Exposure to color film in developers.

Symptoms: Typical itchy papules, typically demarcated by skin lines on extremities, especially the volar aspects.
Specific Signs:
- Wickham's striae: White streaky pattern on papules,
- Koebner's phenomenon: Lesions can develop at sites of trauma,
- Papules may merge to form larger plaques resembling lichen on trees.
- Oral manifestations include white lacy plaques.

Self-limiting with individual lesions lasting for months.
Eruptions typically last for about a year.
As lesions resolve, they become flatter, darker, and may leave discrete brown macules.

Divided into several categories based on:
1. Stage: Acute, subacute, chronic.
2. Age: Infantile, childhood, adult/adolescent, senile.
3. Severity: Mild, moderate, severe.
4. Regional variants.
Complications can lead to generalized exfoliative erythroderma.
Severity of cases can result in complications like hyperpigmentation (PIH) or hypopigmentation.

Criteria for Diagnosis:
- Major criteria (all three required):
- Pruritus (itching),
- Eczematous dermatitis with typical morphology and distribution,
- Chronic, relapsing history.
- Non-essential criteria include:
- Onset before age 2,
- Personal/family history of atopic disease,
- Dry skin within the past year.
Importance: Laboratory tests or skin biopsies are generally unnecessary for diagnosis.

Children: More common in boys.
Adults: More common in women due to the influence of sex hormones.
- Mast cells have androgen receptors; androgens can have an inhibitory effect.
- Estrogens may increase IgE production from B cells.
- Testosterone substitution has shown improvement in patients with hypogonadism.

Management includes:
- Avoiding triggers such as irritants, allergens, and microbial agents.
- Skin care to bolster the impaired epidermal barrier function.
- Anti-inflammatory therapy for controlling inflammation.
- Adjunctive or complementary modalities in selected cases.
Management strategic levels:
- Mild: Continuous use of emollients, intermittent low-potency topical corticosteroids for flares.
- Moderate: May require proactive maintenance with anti-inflammatory agents.
- Severe: May necessitate phototherapy and systemic drugs.

Definition: Discrete pink areas of swelling in superficial skin or mucosa with pruritus; lasts less than 24 hours and may or may not include angioedema.
Classification:
- Acute urticaria lasts fewer than 6 weeks;
- Chronic urticaria persists longer than 6 weeks.

Definition: Acute, often self-limited skin condition typically linked to infections (mainly herpes) or medications.
Presentation: Abrupt onset of target lesions on face and distal extremities, characterized by:
- Dusky circinate plaques with concentric rings of color,
- May include bullae, vesicles, or crust in center.

Definitions:
- Vesicle: Raised lesion less than 0.5 cm in diameter containing fluid.
- Bulla: Raised lesion larger than 0.5 cm in diameter containing fluid.

Definition: A group of diseases characterized by blistering of skin and mucous membranes.
Pathophysiology: Involves auto-antibodies against desmogleins and desmocollins affecting the epidermis and mucosal surface.
Primary Lesions: Flaccid, thin-walled blisters that are easily ruptured; they may arise on normal-looking skin or erythematous bases on mucous membranes and eventually involve other areas.
Clinical Sign: Positive Nikolsky's sign.
Typical Age of Onset: Between 50 and 60 years.
Complications: Common secondary infections and imbalances in fluid and electrolytes.

Acantholysis: Keratinocytes detaching from each other within the blister.
Immunopathological Findings: Presence of auto-antibodies, usually IgG, directed against intercellular substances of the epidermis.
- In pemphigus vulgaris, the predominant auto-antibody is against desmoglein 3; in more superficial forms, it is desmoglein 1.

Routine Histology: Examination of lesional samples in formalin from the edge of a bulla.
Direct Immunofluorescence: Sampling from perilesional skin for antibody detection.
Electron Microscopy: Advanced imaging to assess the blistered areas.

With appropriate glucocorticoid and immunosuppressive therapy, the mortality rate of pemphigus vulgaris patients over a follow-up period of 4 to 10 years is approximately 10%.