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Eczema, Psoriasis, Cutaneous Infections, Acne, and Other Common Skin Disorders¶

Chapter 60 | Part 2: Cardinal Manifestations and Presentation of Diseases · Part 2 – Cardinal Manifestations & Presentation · Chapter 60

Key Clinical Points¶

Atopic Dermatitis (AD) is characterized by an impaired epidermal barrier (filaggrin mutation) and immunoregulatory abnormalities (increased IgE, impaired delayed-type hypersensitivity).
Psoriasis is a T-cell mediated immune-mediated disease with distinct clinical forms: plaque-type (most common), inverse, guttate, and pustular.
Lichen planus is a papulosquamous disorder featuring '6 Ps' (purple, polygonal, pruritic) and Wickham's striae; it may involve mucous membranes and nails.
Pityriasis rosea typically presents as a self-limited eruption with a 2–6 cm herald patch followed by a 'Christmas tree' distribution of scaly papules.
Stasis dermatitis results from venous incompetence and is managed with leg elevation and 30–40 mmHg compression stockings.
Cutaneous infections include Impetigo (S. aureus, Group A β-hemolytic streptococci), Dermatophytosis (KOH+ branching hyphae), Candidiasis (satellite pustules), and Tinea versicolor (Malassezia furfur).
Seborrheic dermatitis is characterized by greasy scales on erythematous patches, commonly in the scalp and face.
Acne rosacea presents with a triad of erythema, telangiectasia, and inflammatory papules/pustules; Acne vulgaris involves comedones and inflammatory lesions.

DEFINITION & OVERVIEW¶

• Eczema: A reaction pattern presenting with variable clinical findings and the common histologic finding of spongiosis (intercellular edema of the epidermis). It is the final common expression for several disorders. • Atopic Dermatitis (AD): The cutaneous expression of the atopic state, characterized by a family history of asthma, allergic rhinitis, or eczema. • Psoriasis: An immune-mediated disease characterized by erythematous, sharply demarcated papules and rounded plaques covered by silvery micaceous scale. • Lichen Planus (LP): A papulosquamous disorder that may affect the skin, scalp, nails, and mucous membranes. • Pityriasis Rosea (PR): A papulosquamous eruption of unknown etiology, often preceded by a 'herald patch'. • Cutaneous Infections: Includes impetigo, ecthyma, and furunculosis.

EPIDEMIOLOGY¶

• Atopic Dermatitis: Prevalence is increasing worldwide; 50% of patients present within the first year of life; 80% eventually coexpress allergic rhinitis or asthma. • Psoriasis: Affects up to 2% of the world's population; approximately 30% of patients develop psoriatic arthritis (PsA), typically between ages 30 and 50. • Seborrheic Dermatitis: A common, chronic disorder frequently seen in patients with Parkinson's disease, stroke, or HIV infection.

ETIOLOGY & PATHOPHYISIOLOGY¶

Atopic Dermatitis Pathophysiology¶

• Genetic Predisposition: Mutation in the gene encoding filaggrin (a structural protein in the stratum corneum). • Immunoregulatory Abnormalities: Increased IgE synthesis, increased serum IgE levels, and impaired delayed-type hypersensitivity reactions. • Epidermal Barrier Defect: Impaired barrier function.

Psoriasis Pathophysiology¶

• Mechanism: T-cell mediated disorder; activated T cells elaborate cytokines responsible for keratinocyte hyperproliferation. • Genetics: 30–50% of patients report a positive family history.

Contact Dermatitis Pathophysiology¶

• Irritant Contact Dermatitis (ICD): Injury caused by an inherent characteristic of a compound (e.g., concentrated acid or base); prior exposure is not necessary. • Allergic Contact Dermatitis (ACD): Delayed-type hypersensitivity mediated by memory T lymphocytes; prior exposure to the offending agent is required.

CLINICAL FEATURES¶

Atopic Dermatitis (AD)¶

• General Features: Pruritus and scratching; course marked by exacerbations/remissions; lichenification of skin; presence of dry skin. • Infantile Pattern: Weeping inflammatory patches and crusted plaques on face, neck, and extensor surfaces. • Childhood/Adolescent Pattern: Dermatitis of flexural skin (antecubital and popliteal fossae). • Adult Patterns: Localized disease (e.g., lichen simplex aureus chronicus or hand eczema); clinical stigmata include perioral pallor, Dennie-Morgan folds, increased palmar markings. • Specific Clinical Types: ◦ Dyshidrotic: Intense pruritic small papules/vesicles on thenar/hypotenar eminences and sides of fingers. ◦ Nummular: Circular or oval 'coinlike' lesions (edematous papules becoming crusted/scaly). ◦ Asteatotic: Mildly inflammatory dermatitis in extremely dry skin (e.g., lower extremities in elderly during winter). • Table 60-1 Summary: Confirms key features including pruritus, exacerbation cycles, and history of atopy.

Psoriasis¶

• General Features: Erythematous, sharply demarcated papules/plaques with silvery micaceous scale; Koebner phenomenon (lesions at sites of trauma). • Clinical Variants: ◦ Plaque-type: Stable, slowly enlarging plaques (most common). ◦ Inverse: Affects intertriginous regions. ◦ Guttate: Small erythematous scaling papules, often following β-hemolytic streptococcal infection. ◦ Pustular: Characterized by fever and a generalized eruption of sterile pustules. • Table 60-2 Summary: Highlights clinical features (e.g., mica-like scale) and histology (acanthosis, vascular proliferation).

Lichen Planus¶

• Morphology: Pruritic, polygonal, flat-topped, violaceous papules with Wickham's striae. • Distribution: Wrists, shins, lower back, genitalia; may involve mucous membranes (buccal mucosa) and nails (lichen planopilaris).

Pityriasis Rosea¶

• Presentation: Herald patch (2–6 cm annular lesion) followed by smaller annular/papular lesions on the trunk. • Pattern: 'Christmas tree' appearance (lesions follow skin tension lines). • Differentiation: Unlike secondary syphilis, palm and sole lesions are extremely rare in PR.

Cutaneous Infections¶

• Impetigo: Honey-colored crusted papules/plaques; caused by S. aureus or Group A β-hemolytic streptococci. • Dermatophytosis: Inflammatory/noninflammatory annular scaly plaques; may involve hair loss; KOH preparation shows branching hyphae. • Candidiasis: Inflammatory papules/plaques with satellite pustules (common in intertriginous areas). • Tinea Versicolor: Hyper- or hypopigmented scaly patches on trunk (Malassezia furfur); 'spaghetti and meatballs' appearance on KOH. • Table 60-5 Summary: Details clinical features, etiologic agents, and treatment for these infections.

Other Conditions¶

• Stasis Dermatitis: Medial ankle involvement; brawny red patches with yellow scale; caused by venous incompetence. • Seborrheic Dermatitis: Greasy scales on erythematous patches; common in scalp, eyebrows, and nasolabial folds. • Acne Rosacea: Erythema, telangiectasia, papules, and pustules (Figure 9). • Acne Vulgaris: Inflammatory papules, pustules, and comedones (Figure 10).

DIFFERENTIAL DIAGNOSIS¶

Psoriasis¶

• Pityriasis rosea • Secondary syphilis

Lichen Planus¶

• Drug-induced eruptions (thiazides, antimalarials) • Chronic graft-versus-host disease • Hepatitis C infection

Stasis Dermatitis¶

• Hypercoagulation • Vasculitis • Arterial insufficiency

INVESTIGATIONS & DIAGNOSIS¶

Clinical Assessment: Visual inspection of morphology, distribution, and history (e.g., identifying 'herald patch' or 'Christmas tree' pattern).
Microscopy:
KOH Preparation: Identify branching hyphae for dermatophytosis.
Diagnostic Criteria:
Atopic Dermatitis: Clinical course lasting >6 weeks with history of atopy.
Psoriasis: Identification of distinct types (Guttate, Pustular, Inverse) to guide management.

MANAGEMENT & TREATMENT¶

Atopic Dermatitis (AD)¶

Avoidance: Eliminate cutaneous irritants.
Moisturization: Apply emollients; use warm/cool water and mild soap for bathing.
Topical Anti-inflammatories:
Low-to-mid potency glucocorticoids.
Non-glucocorticoid agents: Tacrolimus ointment, pimecrolimus cream (TCIs), crisaborole ointment (PDE4 inhibitor), ruxolitinib cream (JAK inhibitor).
Pruritus Control: Topical anti-inflammatories and systemic antihistamines.
Secondary Infection: Treat any secondary infection as identified.

Psoriasis¶

Topical Therapy: Vitamin D analogues, retinoids, and glucocorticoids.
Phototherapy: UV-B or PUVA.
Systemic Agents (Table 60-3):
Methotrexate (Antimetabolite; Weekly)
Acitretin (Retinoid; Daily)
Cyclosporine (Calcineurin inhibitor; Twice daily)
Apremilast (Phosphodiesterase type 4 inhibitor; Twice daily)
Deucravacitinib (Tyrosine kinase 2 inhibitor; Daily)
Biologics (Table 60-4):
Anti-TNF-α: Etanercept, Adalimumab, Certolizumab, Infliximab, Golimumab.
Anti-IL-23: Risankizumab, Tildrakizumab, Guselkumab.
Other IL-inhibitors: Secukinumab, Ixekizumab, Brodalumab.
Warning: TNF-α inhibitors require caution in patients with congestive heart failure (CHF).

Stasis Dermatitis¶

Leg elevation.
Compression stockings (30–40 mmHg).

Cutaneous Infections¶

Impetigo: Systemic or topical antistaphylococcal and antistreptococcal antibiotics.
Dermatophytosis: Topical azoles; systemic griseofulvin, terbinafine, or azoles.
Candidiasis: Topical nystatin or azoles; systemic azoles for resistant disease.
Tinea versicolor: Topical selenium sulfide lotion or azoles.

PROGNOSIS & COMPLICATIONS¶

• Psoriasis: 30% of patients develop psoriatic arthritis (PsA). • Atopic Dermatitis: Chronic cases may lead to lichenification and secondary infections. • Stasis Dermatitis: Requires exclusion of hypercoagulation, vasculitis, or arterial insufficiency.

SPECIAL CONSIDERATIONS¶

Drug Contraindications & Monitoring¶

• TNF-α inhibitors: Caution in patients with congestive heart failure (CHF). • Cyclosporine: Monitor for renal dysfunction, hypertension, hyperkalemia, and hyperlipidemia. • Methotrexate: Monitor for hepatotoxicity, pulmonary toxicity, and pancytopenia.

KEY PEARLS & CLINICAL TRAPS¶

• Atopic Dermatitis is often described as 'an itch that rashes.' • Psoriasis: Differentiation of types (Guttate, Pustular, Inverse) is critical for diagnosis. • Lichen Planus: Associated with Hepatitis C and certain drugs (thiazides, antimalarials). • Pityriasis Rosea: Look for the 'herald patch' and 'Christmas tree' distribution. • Stasis Dermatitis: Requires 30–40 mmHg compression stockings. • Biologics: Anti-IL-23 agents include Risankizumab, Tildrakizumab, and Guselkumab.

Reference Tables¶

TABLE 60-1 Clinical Features of Atopic Dermatitis 1. Pruritus and scratching 2. Course marked by exacerbations and…¶

Harrison's 22e, p.383

1. Pruritus and scratching
  2. Course marked by exacerbations and remissions
  3. Lesions typical of eczematous dermatitis
  4. Personal or family history of atopy (asthma, allergic rhinitis, food allergies,
  or eczema)
  5. Clinical course lasting >6 weeks
  6. Lichenification of skin
  7. Presence of dry skin

TABLE 60-2 Papulosquamous Disorders Psoriasis¶

Harrison's 22e, p.386

	CLINICAL FEATURES	OTHER NOTABLE FEATURES	HISTOLOGIC FEATURES
Psoriasis	Sharply demarcated, erythematous plaques with mica-like scale; predominantly on elbows, knees, and scalp; atypical forms may localize to intertriginous areas; eruptive forms may be associated with infection	May be aggravated by certain drugs, infection; severe forms seen in association with HIV	Acanthosis, vascular proliferation
	Purple polygonal papules marked by severe pruritus; lacy white markings, especially associated with mucous membrane lesions	Certain drugs may induce: thiazides, antimalarial drugs
Pityriasis rosea	Rash often preceded by herald patch; oval to round plaques with trailing scale; most often affects trunk; eruption lines up in skinfolds giving a “fir tree–like” appearance; generally spares palms and soles	Variable pruritus; self-limited, resolving in 2–8 weeks; may be imitated by secondary syphilis	Pathologic features often nonspecific
	Polymorphous appearance depending on dermatophyte, body site, and host response; sharply defined to ill-demarcated scaly plaques with or without inflammation; may be associated with hair loss	KOH preparation may show branching hyphae; culture helpful

TABLE 60-3 FDA-Approved Systemic Therapy for Psoriasis AGENT Methotrexate Acitretin Cyclosporine Apremilast…¶

Harrison's 22e, p.387

AGENT	MEDICATION CLASS	ADMINISTRATION		ADVERSE EVENTS (SELECTED)
		ROUTE	FREQUENCY
Methotrexate	Antimetabolite	Oral	Weekly	Hepatotoxicity, pulmonary toxicity, pancytopenia, potential for increased malignancies, ulcerative stomatitis, nausea, diarrhea, teratogenicity
	Retinoid	Oral	Daily
Cyclosporine	Calcineurin inhibitor	Oral	Twice daily	Renal dysfunction, hypertension, hyperkalemia, hyperuricemia, hypomagnesemia, hyperlipidemia, increased risk of malignancies
	Phosphodiesterase type 4 inhibitor	Oral	Twice dailya
Deucravacitinib	Tyrosine kinase 2 inhibitor	Oral	Daily	Upper respiratory infections, elevated creatine phosphokinase, herpes simplex reactivation, folliculitis

TABLE 60-4 FDA-Approved Biologics for Psoriasis or Psoriatic Arthritis¶

Harrison's 22e, p.387

MECHANISM OF ACTION	AGENTS (INDICATION; ROUTE)	FREQUENCY	WARNINGS, SELECTED
Anti-TNF-α	Etanercept (Ps, PsA; SC) Adalimumab (Ps, PsA; SC) Certolizumab (Ps, PsA; SC) Infliximab (Ps, PsA; IV) Golimumab (PsA; SC)	Ranges from once or twice weeklya to every 8 weeksa	Serious infections, hepatotoxicity, CHF, hematologic events, hypersensitivity reactions, neurologic events, potential for increased malignancies
	Ustekinumab (Ps, PsA; SC)	Every 12 weeksa
Anti-IL-23	Risankizumab (Ps; SC) Tildrakizumab (Ps; SC) Guselkumab (Ps; SC)	Ranges from every 8–12 weeksa	Serious infections, headaches
	Secukinumab (Ps, PsA; SC) Ixekizumab (Ps; SC) Brodalumab (Ps; SC)	Ranges from every 2–4 weeksa

TABLE 60-5 Common Skin Infections Impetigo Dermatophytosis¶

Harrison's 22e, p.388

	CLINICAL FEATURES	ETIOLOGIC AGENT	TREATMENT
Impetigo	Honey-colored crusted papules, plaques, or bullae	Group A Streptococcus and Staphylococcus aureus	Systemic or topical antistaphylococcal and antistreptococcal antibiotics
	Inflammatory or noninflammatory annular scaly plaques; may involve hair loss; groin involvement spares scrotum; hyphae on KOH preparation	Trichophyton, Epidermophyton, or Microsporum spp.
Candidiasis	Inflammatory papules and plaques with satellite pustules, frequently in intertriginous areas; may involve scrotum; pseudohyphae on KOH preparation	Candida albicans and other Candida spp.	Topical nystatin or azoles; systemic azoles for resistant disease
	Hyper- or hypopigmented scaly patches on trunk; characteristic mixture of hyphae and spores (“spaghetti and meatballs”) on KOH preparation	Malassezia furfur