Chapter 13. Rash

Kara N. Shah

Dermatologists define several broad categories of skin disease based on clinical features and pathophysiology. The categories that are of primary interest from an infectious disease perspective include bacterial and mycobacterial infections, fungal infections, protozoal infections, viral infections, reactive erythemas, drug- and viral-induced hypersensitivity syndromes, and vasculitic diseases and purpura (Table 13–1).

Table 13–1. Diagnostic Categories of Selected Infectious and Non-Infections Etiologies of Rashes

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Table 13–1. Diagnostic Categories of Selected Infectious and Non-Infections Etiologies of Rashes

Diagnostic Category

Examples

Bacterial and mycobacterial infections

Cellulitis
Impetigo
Staphylococcal-scalded skin syndrome
Toxic shock syndrome
Ecthyma
Ecthyma gangrenosum
Meningococcemia
Rocky mountain spotted fever
Rickettsialpox
Cutaneous tuberculosis
Cutaneous anthrax
Nontuberculous (atypical) mycobacterial infections
Leprosy
Secondary syphilis
Ulceroglandular tularemia
Actinomycosis

Viral infections

Erythema infectiosum (parvovirus B19 infection)
Papular purpuric socks and gloves syndrome (parvovirus B19 infection)
Infectious mononucleosis (Epstein–Barr virus (EBV) infection)
Roseola infantum (human herpesvirus-6 and human herpesvirus-7 infection)
Rubeola (measles)
Hand-foot-and-mouth disease (coxsackie virus infection)
Herpangina (coxsackie virus infection)
Varicella
Herpes zoster
Cutaneous herpes and herpetic whitlow
Herpes labialis
Herpetic gingivostomatitis
Eczema herpeticum
Molluscum contagiosum
Warts (verruca vulgaris, verruca plana, verruca plantaris, condylomata acuminata)
Smallpox

Fungal infections

Dermatophyte infections (tinea capitis, tinea corporis, tinea pedis, onychomycosis)
Tinea versicolor
Cutaneous candidiasis
Subcutaneous mycoses (sporotrichosis)
Systemic mycoses (blastomycosis, histoplasmosis, coccidiomycosis)
Opportunistic mycoses (aspergillosis, mucormycosis, cryptococcosis)

Protozoal infections

Cutaneous leishmaniasis
Muocutaneous leishmaniasis

Reactive erythemas

Erythema multiforme
Urticaria
Serum sickness and serum sickness-like reactions
Erythema marginatum (acute rheumatic fever)
Erythema chronicum migrans (Lyme disease)

Hypersensitivity syndromes

Morbilliform drug eruption
Stevens–Johnson syndrome
Toxic epidermal necrolysis
Drug reaction with eosinophilia and systemic symptoms

Vasculitic diseases and purpura

Rocky mountain spotted fever
Erlichiosis
Purpura fulminans
Kawasaki disease
Hypersensitivity (leukocytoclastic) vasculitis

Establishing the differential diagnosis of a rash relies both on an appropriately focused history and on correctly describing the morphology and distribution of the rash. A brief overview of common terms used in dermatology is presented in Table 13–2. Common patterns of distribution are presented in Table 13–3.

Table 13–2. Common Morphologic Patterns of Dermatologic Disease

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Table 13–2. Common Morphologic Patterns of Dermatologic Disease

Morphology

Description

Examples

Primary lesions

Macule