Skin Infections Review for the Physician Assistant Exam
For the Physician Assistant Exam (PANCE), you need to be familiar with various types of skin infections, from bacterial infections to viral infections to cutaneous fungal infections. You’ll see many of these conditions clinically.
How to treat bacterial infections
Most skin infections are caused by Strep or Staph bacteria and can be treated with antibiotics.
Cellulitis is a very common bacterial skin infection that you’ve probably encountered in your clinical rotations. It can involve the skin and the subcutaneous tissues. For cellulitis to occur, the person has to have some break in the integrity of the skin, allowing normal skin flora to penetrate. A classic clinical presentation is a lower-extremity cellulitis in someone who’s obese, with corresponding venous insufficiency. Diabetes may be present.
Risk factors for cellulitis include a lowered immune system (for example, diabetes, atherosclerosis, and vascular disease). Presenting symptoms can include a fever, and a leukocytosis may or may not be present. The area affected may also have some degree of adenopathy (for example, inguinal adenopathy for a cellulitis affecting the leg). The most common offending organisms are Staph and Strep species.
Antibiotics can be oral or intravenous, depending on how much the cellulitis has spread. Penicillins and cephalosporins are commonly used. Examples include the first-generation cephalosporins cephalexin (Keflex) and cefazolin (Ancef).
When someone comes to the hospital with a cellulitis, a black magic marker should be used to mark the edge of the cellulitis on admission. With the administration of intravenous antibiotics, the cellulitis should get better and not spread beyond the marker line.
Erysipelas is a skin infection that doesn’t go as deep as cellulitis can. It’s actually superficial edematous cellulitis, characterized by raised borders, that is tender to palpation. It’s usually caused by group A beta-hemolytic Streptococci. The spectrum of antibiotics used to treat erysipelas is the same as with cellulitis, namely penicillins and cephalosporins. Macrolide antibiotics can also be used.
Impetigo is another superficial skin infection also caused by Strep or Staph species. Rather than being maculopapular, it’s a more vesicular/crusting type of honeycomb or honey-crusted lesion. It can look like dried pie crust. A classic area where impetigo can appear is underneath the nose.
Candida and Dermatophyte
Candida can also affect the skin; the medical name for this condition is cutaneous candidiasis. The most common clinical presentation is a skin rash that occurs in the intertriginous areas (under the skin folds) of someone who is massively obese or of a woman with pendulous breasts.
Take a dark, moist place, and you have the right setup for Candida infection. For example, diaper rash is in some cases actually a Candida infection. In addition to maintaining good hygienic practices, you can treat cutaneous candidiasis with topical antifungals such as ketoconazole (Nizoral). They can be creams or powders. Clinically, for skin folds, powder is probably better. It’s also good for diaper rash.
Dermatophyte infections refer to superficial fungal infections that can affect the skin, hair, and nails. The fungus is often named for the site of the infection. Here’s a quick rundown of some of these dermatophyte infections:
Tinea pedis (athlete’s foot): The most common place to get athlete’s foot is between the toes, especially the third, fourth, and fifth toes. In addition to good foot hygiene, the treatment is a topical antifungal ointment. Because athlete’s foot causes such a break in skin integrity, there’s a risk of a bacterial superinfection.
Tinea corporis (ringworm): This is a common form of fungal infection that occurs on the upper and lower extremities. The skin lesion is usually circular. You see a thick and scaly circular border with central clearing. If you see this description on the PANCE, think about tinea corporis.
Tinea capitis: This condition, which is one of the most common superficial skin infections in children, affects the scalp.
You’re examining an 18-year-old male athlete who presents with itching around the groin area that’s been occurring for a couple of days. He denies being sexually active and denies any penile discharge. On examination, you see what looks like red patches around the groin area that are an angry red. Which condition does he most likely have?
(A) Contact dermatitis
(B) Tinea cruris
(C) Gonococcal infection
(D) Tinea corporis
The correct answer is Choice (B). This athlete, who likely wears an athletic supporter, has tinea cruris, also known as jock itch or crotch rot. With Choice (A), contact dermatitis, you’d expect a larger skin area, such as the arm or torso, to be affected.
This man isn’t sexually active, making Choice (C), gonococcal infection, less likely. Choice (D), tinea corporis, is a type of dermatophyte infection that occurs on the arms and legs. Choice (E), eczema, is similar to contact dermatitis in presentation.
Here are a couple of viruses you should know:
Molluscum contagiosum: This skin condition is caused by the pox virus. The skin lesions first begin looking like a run-of-the-mill papular rash; they then transform into what looks like clear pearls that are umbilicated in the center. They usually occur in the genital area in adults; in children they most commonly occur on exposed skin sites. This condition is transmitted by skin contact.
Unlike herpes simplex virus, molluscum contagiosum shouldn’t cause pain. These skin lesions often need to be surgically removed because there isn’t a topical or medicinal treatment for them.
Verrucae (plantar warts): These firm, calloused lesions on the plantar surface of the foot are caused by the human papillomavirus. They can cause pain when walking. The subtypes that cause plantar warts differ from the subtypes that cause condyloma acuminata. Plantar warts can be transmitted from one person to another. They often resolve without treatment, although treatment can involve the use of topical salicylate derivatives or surgical removal.