Dermatological Manifestations of Infectious Disease

Nomenclature

Rash – must be considered as one facet of a disease process. Time course of the development and evolution of the rash is critical for making the correct Diagnosis. Often must wait to see what it turns into

Exanthem: A skin eruption operating as an integral part of an infectious disease

Enanthem: corresponding mucous membrane changes to an exanthem

Description of Rash:

Macule: a circumscribed discoloration of the skin, not raised above the surface of the surrounding skin. Macules often evolve into papules and many rashes are a combination of both (maculo-papular).

Papule: a small nodular elevation of the skin, commonly found in the early stages of chicken pox and smallpox.

Vesicle is a small blister containing clear or relatively clear fluid, scattered irregularly over the skin or grouped in clusters.

Pustule, a small elevation of the skin containing purulent or purulent-appearing liquefied material.

Pustules formed directly as a result of local or systemic sepsis or evolve from a vesicle.

Crusts or scabs: congealed exudates on the skin, very often a late stage in the evolution of vesicular eruptions.

Wheal is a localized effusion of fluid into the skin producing a raised, white or pinkish-white area with a halo of erythema.

vary in size but never rupture.
are characteristic of allergic rashes, being especially prominent in serum sickness.

Erythema: a diffuse or localized redness of the skin,

usually blanches with pressure (generally represents dilatation of capillaries and other small blood vessels).
Intense erythema may not blanch, but lead to edema and blister formation.

Purpuric rashes: small hemorrhages beneath the epidermis (petechia) or larger areas of hemorrhage (ecchymosis)

In infectious diseases, these hemorrhagic lesions often precede a more specific eruption or evolve during an exanthem.

with intense erythema Þ pain, induration, and tenderness if deeper soft tissue structures are involved

without intense erythema capillary dilatation may ultimately produce translocation of RBCs into the skinÞ no blanching .

Some Agents Responsible

Streptococcus

particularly beta-hemolytic streptococcus, is capable of producing a variety of skin lesions, including:
blanching erythema associated with the toxin-mediated capillary dilatation of scarlet fever,
the tiny petechial hemorrhage (into the conjunctiva or underneath the fingernail) reflecting
an endovascular infectious focus on a heart valve (in endocarditis),
or directly infecting tissue and producing cellulitis and/or a necrotizing fasciitis
erythema marginatum – immunologically-mediated – associated with rheumatic fever – uncommon in USA today.

Staphylococcus aureus shares many versatile properties with the streptococcus, but has many unique mechanisms.

Some Dermatological Manifestations of Infectious Disease

Impetigo: initially vesicular, later crusted, superficial dermal infection

group A streptococci is usual agent and is usually seen in children.

Staphylococcus aureus is increasingly involved, either alone or in combination with a group A streptococcus.
Histopathology: a superficial, intraepidermal, vesiculopustular lesion.

Gram stain of these vesicles show gram (+) cocci in chains or clusters, depending on predominant organism.
The lesions remain superficial and do not ulcerate or infiltrate the dermis

mild regional lymphadenopathy is common. Healing occurs without scarring, the lesions are painless

constitutional manifestations are surprisingly minimal.

Furuncle: a deep inflammatory nodule, usually developing from a preceding folliculitis, a pyoderma located within hair follicles, in apocrine regions

usually due to Staph. aureus, although Pseudomonas aeruginosa can be acquired from swimming pools and whirlpools

Carbuncle: a more extensive process extending into the subcutaneous fat in areas covered by thick, inelastic skin

multiple abscesses develop, separated by connective tissue septae which drain to the surface along hair follicles;

Staph. aureus is almost invariably the etiologic agent.

Ecthyma: resemble impetigo initially but are capable of penetrating through the epidermis.

Group A streptococci either produce these lesions de novo or secondarily infect pre-existing superficial lesions (insect bites, scratches, etc.) resulting in the same clinical picture.
The same picture may be reproduced in the course of Pseudomonas bacteremia in neutropenic patients.

Chancriform: lesions caused by a large group of locally invasive infectious agents

produce a punched out, necrotizing and destructive lesion (anthrax is one of the most prominent)
(N.B. The chancre of syphilis is not a necrotizing lesion; it is painless and heals without scarring!).

Erysipelas: a distinctive type of superficial cellulitis of the skin with prominent lymphatic involvement

almost always due to group A streptococcus, rarely to S. aureus.
Caused by exotoxin, affects middle aged patients in warm climate, often starts with erythematous cutaneous rash on face

Cellulitis: an acute spreading infection of the skin, which involve the subcutaneous tissues

extends deeper than erysipelas
group A streptococcus or S. aureus is most frequently the etiologic agent.
usually occurs in areas of previous trauma, but can result from hemotogenous spread to skin and subcutaneous tissues.

Infectious gangrene: an often rapidly developing cellulitis with extensive necrosis of subcutaneous tissues and overlying skin.

clinical picture: depends on specific causative organism, the anatomic location of infection and predisposing conditions.
(1) necrotizing fasciitis (streptococcal gangrene)
(2) gas gangrene (clostridial myonecrosis) and anaerobic cellulitis

(3) progressive bacterial synergistic gangrene

(4) synergistic necrotizing cellulitis (perineal phlegmon and gangrenous balanitis).

Pathologic changes of gangrenous cellulitis:

necrosis and some hemorrhage into the skin and subcutaneous tissues
abundant PMNs (although in clostridial myonecrosis: exudate is thin and consists of fluid, fibrin and gas but few WBCs)
fibrin thrombi present in small arteries and veins of the skin and subcutaneous fat, particularly streptococcal gangrene

Crepitant cellulitis characterized by the presence of bubbles of gas within the soft tissue; readily obvious on x-ray.

usually indicates the presence of anaerobic bacteria, alone or in combination with other organisms
is an indication for immediate surgical debridement and removal of obviously infected tissue.

The diabetic foot is particularly prone to polymicrobic infection because of vascular and neuropathic changes

Fournier's gangrene: serious form of necrotizing fasciitis occurring around male genitals, involving 1 or more:

perineum, penis, scrotum, lower abdominal wall
risk factors: DM, local trauma, periurethral extravasation of urine, perirectal or perianal infections, prior surgery

Lymphadenitis: acute or chronic inflammation of lymph nodes, restricted to a solitary node or regional lymphadenitis.

Lymphadenopathy may be generalized during a systemic infection.
Microscopy: non-suppurative, suppurative, granulomatous, or caseous, depending on the nature of the bug.
May or may not progress to abscess formation.
Acute lymphadenitis is associated with pain, erythema and acute lymphedema.
Chronic lymphadenitis has non-specific histology with proliferative hyperplasia of RE cells, and prominent germinal centers in dilated lymph sinuses filled with mononuclear cells. Also seen in patients with a lymphoproliferative disorder.

Lymphangitis: an inflammation of lymphatic channels, usually in the subcutaneous tissues.

either as an acute process of bacterial origin or as a chronic most commonly due to group A streptococci in USA
or subacute process of mycotic, mycobacterial, or filarial etiology.
usually caused by Sporotrichum schenckii, although other agents can produce similar lesions, including various mycobacteria, Nocardia species, and, occasionally, Staph. aureus (botryomycosis).
In the legs, thrombophlebitis may produce linear areas of tender erythema, usually without tender regional adenopathy,
distinguishes it from lymphadanitis.

Filariasis is a consideration when an appropriate geographic history is obtained.

Sporotrichosis is considered when chronic ulcerative lymphangitis develops in patient working with plants, soil or timber.

Mycobacterium marinum is suggested etiologically when "sporotrichoid" lesions develop in a person who has been around swimming pools and fish tanks.