Dermatology - Skin infections/ infestations Flashcards
What is erysipelis and cellulitis?
These are spreading bacterial infections of the skin.
Cellulitis = deep cutaneous tissue
Erysipelis = acute superficial form of cellulitis and involves the dermis and upper subcutaneous tissue
What causes erysipelis and cellulitis?
They are both caused by either streptococcus pyogenes or staph aureus.
Risk factors include - immunosuppression, wounds, legs ulcers, toeweb intertrigo (inflammation of the body folds) and minor skin injury
How does cellulitis present?
It most commonly affects the lower limbs.
Local signs of inflammation - swelling, erythema, warmth, pain; may be associated lymphangitis.
Systemically unwell with fever, malaise or rigors, particularly with erysipelis.
Note that cellulitis is usually unilateral.
How is erysipelis distinguished from cellulitis?
Erysipelis is distinguished by a well defined, red, raised border.
What is the criteria for admission with cases of cellulitis?
Eron classification helps guide management - 4 classes:
Class I = no signs of systemic toxicity and the person has no uncontrolled comorbidities
Class II = The person is either systemically unwell or systemically well but with a co-morbidity (for example peripheral arterial disease, chronic venous insufficiency, or morbid obesity) which may complicate or delay resolution of infection
Class III = The person has significant systemic upset such as acute confusion, tachycardia, tachypnoea, hypotension, or unstable co-morbidities that may interfere with a response to treatment, or a limb-threatening infection due to vascular compromise
Class IV = The person has sepsis syndrome or a severe life-threatening infection such as necrotizing fasciitis
Based on this, the following should be admitted:
- Eron class III and IV
- rapidly deteriorating cellulitis
- is very young
- has significant lymphoedema
- has facial or periorbital cellulitis
How is cellulitis/ erysipelis treated?
Flucloxacillin is the first line antibiotic for mild/ moderate cellulitis. Clarithromycin (macrolide) or clindamycin is recommended for patients allergic to penicillin. Many protocols now recommend oral clarithromycin for those patients who have failed to respond to penicillin.
Severe cellulitis should be treated with intravenous benzylpenicillin + flucloxacillin
What is staphylococci scalded skin syndrome?
This infection is commonly seen in infancy and childhood. It is caused by production of circulating epidermolytic toxin from phage group II, benzyl-penicillin resistant (coagulase positive) staph.
A key thing to remember is that ALL staph are catalse positive (this differentiates them from strep which are also gram positive cocci but group in lines rather than clusters), but only staph aureus is coagulase positive.
What is the presentation of scalded skin syndrome?
It normally develops within a few hours to days and may be worse over the face, neck, axillae or groins.
A scald like appearance is followed by large flaccid bulla.
Peri-oral crusting is typical.
There is intraepidermal blistering in this condition.
Lesions are very painful.
Recovery is within 5-7 days.
How is scalded skin syndrome managed?
Antibiotics (e.g. systemic penicillinase resistant penicillin, fusidic acid, erythromycin or appropriate cephalosporin)
Analgesia
What is impetigo?
Impetigo is a common, highly contagious, superficial bacterial infection of the skin. It is caused by either staph aureus or strep pyogenes. Co-existing skin conditions, such as abrasions, infestations or eczema, predispose to impetigo.
What are the 2 presentations of impetigo?
In non-bullous impetigo, a thin walled vesicle develops , ruptures rapidly and is rarely seen intact. Dried exudate, forming “golden crusting” arises on an erythematous base.
In bullous disease, the toxins cleave the superficial epidermis, causing intact blisters containing clear fluid to appear, lasting 2-3 days. The face scalp and limbs are most commonly infected but sites of eczema can also be involved. Constitutional symptoms are uncommon.
How is impetigo managed?
A bacterial swab should be taken from blister fluid or active lesion before treatment. One third of the population are nasal carriers of staphyloccocus, so nasal swabs should be obtained.
In mild localised disease, topical treatment with mupirocin or fusidic acid usually suffices and limits spread. Staphyloccoci nasal carriage should be treated with topical mupirocin. In severe cases, oral flucloxacillin or erythromycin (if penicillin allergic) is indicated. If a nephritogenic streptococcus is suspected, systemic antibiotics should be given, as post streptotoccal glomerulonephritis can occur.
What is folliculitis?
Folliculitis is inflammation involving the hair follicle. This can be superficial, just involving the ostium of the hair follicle (folliculitis) or deep (faruncles and carbuncles).
What is superficial folliculitis? What is the clinical course?
This is very common, usually minor and subacute or chronic. It is often infective, caused by staph aureus, but can also be due to physical (e.g. mechanical epilation) or chemical (e.g. mineral oils) injury. In these cases, the folliculitis is usually sterile. Staphylococcal folliculitis is most common in children and often occurs on the scalp or limbs. The pustules usually heal in 7-10 days but can become more chronic and in older children and adults can progress to a deeper form of folliculitis.
What is deep folliculitis?
Deep folliculitis can cause either faruncles or carbuncles.
Faruncles - (boil) is an acute staph aureus infection of the hair follicle, which becomes pustular and fluctuant and is often exquisitely tender. The lesions eventually rupture to discharge pus and, because they are deep, leave a scar.
Carbuncles - this can progress from a faruncle, and is an exquisitely tender nodule, often on the neck, shoulders or hips, and is associated with severe constitutional symptoms. It implies the involvement of several contiguous (touching), hair follicles. Treatment, as with faruncles, is with appropriate anti-staph antibiotics.
What is erythrasma? How is it diagnosed?
Erythrasma is a generally asymptomatic, flat, slightly scaly, pink or brown rash usually found in the groin or axillae. It is caused by an overgrowth of the diphtheroid Corynebacterium minutissimum.
Examination with Wood’s light reveals a coral-red fluorescence.
Topical miconazole or antibacterial are usually effective. Oral erythromycin may be used for more extensive infection.
What herpes viruses infect the skin?
Herpes simplex virus 1 and 2 both infect the skin.
Type 1 herpes simplex virus (HSV) typically produces mucocutaneous lesions of the head and neck, while type 2 predominantly affects the genital tract.
Virus shed by infected individuals infects via a mucosal surface of a susceptible person. HSV infects sensory and autonomic nerve ganglia and episodes of reactivation occur throughout life, precipitated by stress, trauma, illness or immunosuppression. Primary infection normally occurs causing vesiculating gingivostomatitis. It may also present as keratitis (dendritic ulcer), viral paronychia, vulvovaginitis, cervicitis, balanitis, or rarely as encephalitis. Diagnosis is by PCR, electron microscopy or culture.
What are the complications of herpes virus infection?
- corneal dendritic ulcers; may produce scarring
- encephalitis; preferentially affects the temporal lobe
- HSV infection in patients with eczema; can result in disseminated skin lesions (eczema herpeticum)
- neonatal HSV infection; may be disseminated and potentially fatal
How should herpes viral infection be managed?
Treatment is with antiviral agents such as aciclovir; best results are achieved with early treatment.
What virus is associated with AIDS and causes Kaposi’s sarcoma?
Human herpes virus 8.
The virus which spreads via saliva, causes Kaposi’s sarcoma in both AIDS related and endemic non-AIDS related forms.
What enterovirus infections are associated with skin disease?
1) Hand foot and mouth disease - a mild febrile illness affecting children, mainly in the summer months, and caused by Coxsackie virus or echoviruses. There is fever, lymphadenopathy, mouth ulceration and a vesicular eruption on the hands and feet
2) Herpangina - causes discrete vesicles on the palate associated with high fever, sore throat and headache.
Both of these conditions are self limiting WITHOUT treatment.
What poxvirus infections are associated with the skin?
These DNA viruses are potentially pathogens but nowadays rarely cause significant human disease. They include smallpox, monkey pox and cow pox, as well as orf and molluscum contagiosum.
Smallpox (variola) - this severe disease, with a high mortality in the unvaccinated, was eradicated worldwide in 1980 following an international vaccination campaign. The classical form is characterised by a typical centrifugal vesicular/ pustular rash, worst on the face and extremities, with no cropping (i.e. unlike chickenpox) and accompanied by fever, severe myalgia and odynophagia.
What viruses cause warts?
Viral warts are caused by the DNA human papillomavirus (HPV) and are extremely common, being transmitted by direct contact with the virus in either living skin or shed skin fragments. Most people suffer one or more warts at some point during their life. There are >90 different subtypes. HPV subtypes 16 and 18 are spread by sexual contact and are strongly associated with subsequent development of cervical carcinoma. Vaccinations are now available against HPV-16 and 18 and are recommended for adult females before they become sexually active. Immunosuppressed patients are at greater risk of infection with HPV.
What are the clinical features of viral warts?
Common warts appear initially as smooth, skin coloured papules. As they enlarge, their surface becomes irregular and hyperkeratotic producing the typical warty appearance. One method of classifying warts is based on their clinical appearance:
- PLANTAR WARTS (varrucae): found on the sole of the foot, these are characterised by a horny collar surrounding a roughened surface. Paring reveals capillary loops that distinguish plantar warts from corns
- MOSAIC WARTS: mosaic like sheets of warts
- PLANE WARTS: smooth, flat topped papules, usually on the face and dorsum of the hands
- FILIFORM WARTS: often found on the face
- GENITAL WARTS: papillomatous and protuberant
How should warts be managed?
Most viral warts resolve spontaneously but often very slowly. Therapeutic options to speed resolution include:
- topical salicylate acid (first line)
- cryotherapy
- Imiquimod or podophyllin for genital warts
- intralesional bleomycin (for recalcitrant warts)
What is molluscum contagiosum?
Molluscum contagiosum is caused by a DNA poxvirus infection. It can affect any age group but usually targets children over the age of 1 and the immunosuppressed. The classic lesion is a dome shaped, “umbilicated”, skin coloured papule with a central punctum. Lesions tend to be multiple and are often at sites of apposition, such as the side of the chest and the inner arm. No treatment is required, as these lesions resolve spontaneously but can take several months. If active resolution is sought, curettage or cryotherapy can be tried, or topical agents such as salicylate, or podophyllin or imiquimod.
What patients are at risk of Orf infection?
Orf is an occupational hazard for those who work with sheep and goats. It is a cutaneous infection with a parapoxvirus carried by these animals. Innoculation of the virus, usually into the skin of a finger, causes significant inflammation and necrosis, which resolves within 2-6 weeks. No specific treatment is available unless there is evidence of secondary infection. Erythema multiforme can be triggered by orf virus infection.
