Changes of the Skin Due to Infection

 Bacterial infection can affect the skin alone (follicular and nonfollicular types) or involve the skin secondarily in the setting of systemic infection.
 
➤ The more common types of localized, nonfollicular bacterial infection are impetigo contagiosa, ecthyma, and erysipelas.
➤ Rarer varieties include erysipeloid(a warm, erythematous area, usually on the hands) and cutaneous diphtheria, which is usually seen in persons with poor hygiene and in travelers returning from the tropics. It manifests as punched-out ulcers covered with a greasy, yellowish-gray pseudomembrane.
 
➤ A common finding in cat-scratch disease is an inflamed wound in the hand associated with prominent lymphadenopathy.

➤ Actinomycosis is characterized by firm inflammatory nodules, most commonly found at the angle of the jaw, with a tendency to form fistulae.
 
➤ Nocardiosis is another possible cause of chronic abscesses and fistulae.
 
➤ Bacillary angiomatosis (Bartonella sp.) is a very rare disease that manifests itself with dark red or bluish papules and nodules. It is seen almost exclusively in HIV-positive individuals.
 
➤ The classic cutaneous manifestation of anthrax is a painless papule that develops into a hemorrhagic blister on an edematous ground; these are mainly found on the hands.
 
➤ Cutaneous tuberculosis is currently rare. It is found at the portals of entry, usually the face or lower limbs, and most commonly in children; it consists of a painless papule that develops into an ulcer. Lupus vulgaris is a post-primary form of cutaneous tuberculosis that takes a very long course with ulcerating, hyperkeratotic, and sometimes scar-forming lesions.

The following characteristic changes are produced by systemic infections and toxic effects:

➤ Subacute bacterial endocarditis can cause petechiae, subungual splinter hemorrhages, and Osler and Janeway lesions.

➤ Streptococcal infections are sometimes followed by erythema nodosum. In the aftermath of a soft-tissue infection, there may be progressively severe erythema, with the formation of bullae and systemic manifestations of shock (streptococcal toxic shock syndrome).

➤ Staphylococcal infections can produce staphylococcal toxin, with major clinical effects. The staphylococcal scalded skin syndrome usually affects children, while adults usually suffer from toxic shock syndrome, which consists of fever, erythrodermia, hypotonia, and desquamation of the skin, particularly on the hands.

➤ In meningococcal sepsis, urticaria may be present transiently before the classic petechial lesions appear.

➤ Hemorrhagic bullae on an indurated base, which ulcerate and form central black areas of necrosis (ecthyma gangrenosum), are seen in Pseudomonas sepsis.

 
➤ So-called roseola is typical of salmonellosis.

➤ In gonococcal sepsis (the arthritis−dermatitis syndrome), one finds papules and pustules, mainly on the lower limbs, together with joint swelling and tenosynovitis. A similar picture is seen in chronic meningococcal sepsis.


➤ Secondary syphilis can produce a wide variety of exanthems, which often mimic those due to other illnesses (viral exanthems, psoriasis, lichen ruber planus, etc.).
 
➤ Other infectious diseases that involve the skin less commonly include brucellosis, leptospirosis, yersiniosis, and listeriosis.
 
Fungal infections affecting the skin are of various types: superficial fungal infections (dermatophytoses, candidiasis); fungal infections with subcutaneous nodules (sporotrichosis, blastomycosis, coccidioidomycosis); and systemic mycoses with cutaneous manifestations (e. g., histoplasmosis and cryptococcosis).
 
Viral infections involve the skin either by direct exogenous infection (e. g., herpes simplex virus) or as a cutaneous manifestation of systemic disease. Sometimes a clinical diagnosis can be made from the skin lesions alone, because of their characteristic morphology (e. g., varicella, with the simultaneous appearance of vesicles in different stages of development) or mode of appearance (e. g., exanthem beginning behind the ears in measles).

HIV infection produces a number of characteristic skin changes due to various pathogens, depending on the severity of immune compromise.